Transformer Differential Protection Relay Setting Calculation

Transformer Differential Protection Relay Setting Calculation
Transformer Differential Protection Relay Setting Calculation Image link: https://en.wikipedia.org/wiki/Captain_America
C O N T E N T S:

KEY TOPICS

  • The transformer differential protection contains a number of supplementary functions (adaptation to transformation ratio and vector group, stabilisation against in-rush and over-excitation) and therefore requires some fundamental consideration for the configuration and setting calculation.(More…)
  • The sensitivity of the relay for internal faults may be decreased in the same time, particularly in the transformer protection applications.(More…)
  • For internal faults, the fault currents must pass through the exciting branch and high- impedance relay of each CT, so that the CTs are saturated for most faults, Rc a b c Rc Rc Ia Ib Ic Ia Ib Ic Ia Ib Ic Ia Ib Ic Ia Ib Ic Ia Ib Ic 0.5Ia 0.5Ib 0.5Ic GeneratorRc 2 R R op R R op R R op R R R R op R R op FIGURE 8.8 Typical differential (87) connections for the protection of a split-winding generator.(More…)
  • A. Power Equipment 1 KVA 3 phase 415 or 220 Volts alternator coupled to 1.5 HP (Prime mover) with drive unit- 2(Two) sets Resistive load 1-KW for loading the synchronized bus B. Protection RelaysThe Protection Relays incorporated in the Testing Panel should be of ALSTOM / L&T /etc. B1 Over Current Relay Static – 1 No. B2 Earth fault Relay Static – 1 No. B3 Under/Over frequency relay static-1 No B4.(More…)

POSSIBLY USEFUL

  • Usually the only way to cause a properly rated generator CT to saturate is for the system contribution of the available fault current to pass through the CT?s primary, and if this happens, the fault is within the generator?s differential zone of protection anyway, so an 87G trip is expected.(More…)
  • The multifunc- tion digital (microprocessor) relays provide many functions in a single pack- age along with digital fault recording, self-checking, and so on. 8.3 STATOR PHASE-FAULT PROTECTION FOR ALL SIZE GENERATORS Phase faults seldom occur, but when they do, large fault currents can flow.(More…)
  • The new zone settings of the relay R A using the current coefficients ( K 1, K 2 & K 3 ) for different faults with different fault conditions are tabulated in Tables 7, 8 and 9.(More…)

RANKED SELECTED SOURCES

KEY TOPICS

The transformer differential protection contains a number of supplementary functions (adaptation to transformation ratio and vector group, stabilisation against in-rush and over-excitation) and therefore requires some fundamental consideration for the configuration and setting calculation. [1] If the neutral of a star-connected power transformer is earthed, any earth fault in the network will be perceived by the protection relay as differential current. [2] Moreover Buchholz relay is provided in transformer for detecting any internal fault in the transformer but Differential Protection scheme detects the same in more faster way. [3] The differential relays normally response to those faults which occur in side the differential protection zone of transformer. [3]

Now, we need to understand, differential protection activated when differential current deviates from zero or the value which we set in the relay while keeping an eye on that “Predefined very small differential current due to varying tap changer positions and current transformer inaccuracies”. [2]

The transformer differential protection must therefore be stabilized against this phenomenon. [1] Class X current transformer is use in conjunction with high impedance circulating current differential protection relay, eg restricted earth fault relay. [4] These supplement differential protection, but can operate only for faults inside the transformer tank. 8.5 PHASE-FAULT BACKUP PROTECTION (51V) OR (21) Backup protection for the generator and connected system can be provided by a voltage-controlled or voltage-restraint time-overcurrent relay (51V) or by phase distance relays (21). [5] INSTRUCTION MANUAL OVERCURRENT PROTECTION RELAY earth fault element phase protection and earth fault protection or earth fault protection depending on the stricted earth-fault protection, a negative- are available twice: earth-fault differential protection, breaker failure protection and overload protection Principles of Electrical Grounding John Pfeiffer, P. Cookies & Data Protection Sensitive Earth fault Protection scheme is used for the detection of earth fault. [4]

Without breakers between generators and transformer, the overall transformer differential protection must be of the multirestraint type and connected as discussed in Section 9.8. [5] I1F1gen 1:0 0:131 7:62 pu 7:62 3207:5 24; 438:11 A at 18 kV 24; 438:1 1,100 22:2 A sec (8:13) 8.4 UNIT TRANSFORMER PHASE-FAULT DIFFERENTIAL PROTECTION (87TG) Unit transformer differential protection is recommended and is shown as 87TG in Figure 8.5. [5]

The sensitivity of the relay for internal faults may be decreased in the same time, particularly in the transformer protection applications. [6] Objective : To check slope m1, this considers current proportional errors result from transformation errors of the main CTs or the input CTs of the protection relay, mismatching and influence of tap changers in transformers. [7] The V/Hz relay function provides protection for over-excitation conditions, which cause excessive flux density in the generator or transformer. [8] While this has happened, HDC has changed our official recommendation to not having redundant generator protection, but instead having only redundant relays for transformers where the failure of a protective relay would result in multiple units being out of service. [8]

In practice, a small differential current, mainly caused by measuring errors of the current transformers and the relay, can be noticed even though there is no fault within the area of protection. [6] A sufficient similarity in the accuracy limit factors of the current transformers used in the protection further assures that the relay maintains its stability at faults outside the area of protection. [6] On faults inside the area of protection, the current transformers attempt to feed a secondary current proportional to the short-circuit current through the relay. [6]

To reduce the wiring among relays and instrument transformers, ETAP allows protection relays to be connected remotely to CTs and PTs through a newly enhanced remote connector element. [9]

The basic setting must be higher than, for example, the transformer excitation current or the line-charging current at maximum operating voltage to avoid a false operation of the relay. [6] Therefore, the setting for the digital relays needs to be less sensitive to prevent inadvertent operation during external faults and transformer inrush events. [8]

If any major fault occurs inside the transformer due to which the normal ratio of the transformer disturbed then the secondary current of both transformers will not remain the same and one resultant current will flow through the current coil of the differential relay, which will actuate the relay and inter trip both the primary and secondary circuit breakers. [3] In transformer protection applications, a so-called apparent differential current like this is additionally caused by the no-load current of the transformer, the position of the tap changer and momentarily by the transformer inrush current, which fully appears as differential current. [6] Ideally under no faults, No differential current in the circuit, but practically very small differential current due to current transformers inaccuracies and varying tap changer positions, will flow in the protection circuit. [2]

The differential relay provides the primary protection for phase-to-phase faults, and can also detect turn- to-turn faults in multi-turn coils when used with a split-phase winding / ct configuration. [8] When the protection is implemented using a voltage relay, the selected setting must be equal to or exceed the calculated stabilizing voltage. [6] StarZ simulates and evaluates model-specific protection settings and functions similar to the actual relay. [9] In ETAP, the user configures the same settings and protection element outputs as that of the actual relay. [9]

When the ratio between the differential current and the stabilizing current exceeds the settings, the relay operates. [6] When a protected power transformer is energized, the inrush current fully appears as differential current, in which case the stabilization of the relay alone is not enough to prevent false relay operations. [6] The secondaries of both CTs should be connected to the same current coil of a differential relay in such an opposite manner that there will be no resultant current in that coil in a normal working condition of the transformer. [3] The differential relay actually compares between primary current and secondary current of power transformer, if any unbalance found in between primary and secondary currents the relay will actuate and inter trip both the primary and secondary circuit breaker of the transformer. [3]

In these cases, the unsymmetrical phase currents containing second harmonics may cause non-simultaneous saturation of the current transformers and thus apparent differential current for the relay. [6] The idea is to route the apparent differential current formed in the mentioned way to flow through the saturated current transformer rather than through the relay. [6]

Differential relay slope can be tested by first determining the starting point of the slope which is mentioned in the relay setting in the form of restraining current value. [7] HDC relay settings guidelines found in this article are based on experience and lessons learned and evolve over time. [8] Relay settings is an art; using experience as well as lessons learned, we can improve how we implement digital multifunctional relays. [8]

Protections for The protection relay setting must be calculated to calculation of the voltage profiles. (load flow );. [10] Operation & Maintenance Instruction Manual Rho 3 is a multi- function numerical Motor Protection relay resulting in the thermal overload setting of the relay becomes applicable for calculation of relay operating time. [10] A primary motor protective element of the motor protection relay is the used, thermal overload setting can and also use the acceleration thermal limits for TCU calculations. [10]

•One no. of three phase numerical transformer protection relay – % differential relay – Alstom / Areva / Ashida / ABB / L &T/ Reyrolle•3 phase over current relay with high set + Earth fault – Alstom / Areva / Ashida / ABB / &T/ Reyrolle. [11] In such case, under normal condition there will be a flow of net differential current (sum of individual CT secondary current) through the relay and if this value exceeds the setting value then Differential Protection will operate to trip the breaker. [12]

We need to take care of this small very small differential current while working on system else it will cause malfunction of our differential protection scheme. [2] The increased magnetising current appears as a tripping current in the differential protection with large overvoltage. [1] When transformers were connected in parallel, it was observed that the differential protection of the transformer that was in service issued a trip. [1] Differential protection is very useful method of protection that can be applied to the protection of any network component, such as transformers, machines, busbars, lines and feeders. [6] Therefore, differential protection of transformer should be provided with a proportional bias of an amount which exceeds in effect the maximum ratio deviation. [3]

Under this condition differential relay will block tripping by considering that transformer is starting. [7] Here is the IEEE guide to test Numerical Differential relay of the transformer. [7]

Principle of Differential Protection scheme is one simple conceptual technique. [3] Differential protection provides fast and selective short-circuit protection on its own, or as a supplement to Buchholz (gas pressure) protection. [1] Tripping by the differential protection with a fast measurement due to these conditions must be avoided at all cost. [1]

For internal faults, the fault currents must pass through the exciting branch and high- impedance relay of each CT, so that the CTs are saturated for most faults, Rc a b c Rc Rc Ia Ib Ic Ia Ib Ic Ia Ib Ic Ia Ib Ic Ia Ib Ic Ia Ib Ic 0.5Ia 0.5Ib 0.5Ic GeneratorRc 2 R R op R R op R R op R R R R op R R op FIGURE 8.8 Typical differential (87) connections for the protection of a split-winding generator. [5] Definition of sensitive earth fault protection A system of earth fault protection in which the fault current is limited by design to a low value which generally requires amplification in order to operate an earth fault relay. doc Transformer Protection source for additional theory and application fast clearing for close-in external faults is part of the transformer protection scheme. [4]

IDMT Over current & Earth Fault Relay Setting: Calculate IDMT Over Current Relay Setting (50/51) Calculate IDMT Over Current Relay Pick up setting. by time discrimination? s? When a fault occurs, current flows from the power system to earth. fault, which is the signature of a fault that is I. 6 NEUTRAL GROUNDING RESISTOR AND FAIL SAFE RELAY : This relay provides earth fault protection also to save the N. 2. [4] Traditionally, inverse-time overcurrent relays (an inverse-time curve is characterized by the inverse variation of current with the time, as shown in Figure 4) for overload protection, but a difficulty is that transformers are usually outdoors where ambient temperature affects their loadability, and hence the optimum pickup settings of such relays. [13]

As indicated in Section 8.7.1, ground fault protection can also be obtained by supplying a 59G relay from the generator voltage transformers. [5] Many numerical transformer protection relays available today include protection functions that operate on insulating oil temperatures, calculated loss-of-life due to high oil temperature, and predicted oil temperatures due to load. [13]

Many protection systems are required to operate during the period of transient disturbance in the single-phase earth fault. the fault current will be very low and will not be able to activate the earth fault protection relay during earth fault conditions. [4] Illias, P. Faults may also be caused by either short-circuits to earth or between live conductors, or may be caused by broken conductors in one or more phases. 373-ELR Earth Leakage Protection Relay Residual current devices are used to detect potentially dangerous earth fault currents before damage is caused. [4] ” Earth Fault Relays on The balanced earth fault protection scheme is mainly used for protection of small generator where differential and self-balanced protection systems are not applicable. [4] REF Protection Over Fluxing in Transformer In other words, the secondaries of both CTs should be connected to the same current coil of a differential relay in such an opposite manner that there will be no resultant current in that coil in a normal working condition of the transformer. [4]

” Calculating loadability limits of distance relays”: – doi/CPRE. 14 Sep For Motor, Transformer and Generator Differential Protection. [10]

Restricted Earth Fault Protection of Transformer An external fault in the star side will result in current flowing in the line current transformer of the affected phase and at the same time a balancing current flows in the neutral current transformer, hence the resultant current in the relay is therefore zero. phase earth fault currents Relay Theory and Basic System Protection. [4] This protection action time limit, after the set calculation is confirmed, that is, by a special time relay to be guaranteed, the starting time limit and the size of the short-circuit current has nothing to do, so called the fixed-time over-current protection. [14] March 07 MREF (RESTRICTED EARTH FAULT) Technical Manual P&B Engineering (UK) Ltd Belle Vue Works GET-8390: Sensitive Ground Fault Protection in the F60 2 GE Power Management Typical Connections for Ground Fault Protection RESIDUAL CONNECTION The ground fault elements are connected in the common neutral connection of the line CALCULATION OF EARTH FAULT CURRENTS the protection settings concerning their sensitivity and pick-up reliability correctly. [4]

Three-stage current protection refers to the protection of the current instantaneous protection (the first paragraph), the current limit protection (the second paragraph), the definite time over-current protection (the third paragraph) constitute a set of protection, the following we will come to Introduce the working principle and setting calculation method of current protection during the third stage. [14]

Can anyone tell me how to select an appropriate setting for restricted earth fault protection relays used Their Theory and Practice. [4] Installation and Operating Manual System Protection Relay Theory of operation and response time 11 long time standby earth fault 64. [4] The main application is to prevent electrocution but RCDs can also be used to protect equipment, especially against fire. will present relay theory and operation of the older electromechanical as well Ppt on protection of power transformers Restricted earth fault protection is provided in power transformer for sensing internal earth fault of the transformer. [4] Because the protection 1 and 2 are installed in different locations, the characteristics of the current transformers and relays they use are hardly exactly the same. [14]

Ground fault protection is provided, but should be supplemented with 50N51N overcurrent relays connected in the grounded neutral. 8.3.5 PHASE PROTECTION FOR SMALL GENERATORS THAT DO NOT USE DIFFERENTIALS Where small power sources are connected to a large system, protection for phase faults in or reflected in the ac circuits of these small sources can be obtained from instantaneous overcurrent (50) or time-overcurrent (51) relays. [5] The SEL-487 relay has a unique “negative sequence differential” protection element. [15]

The relay starts operating when the magnitude of the fault current is more than that of the relay setting. [16] The large circle setting of the loss-of-field unit (40) will operate for swings passing near and at the bus, and within the unit transformer and generator, but can pass out before the (40) relay times out. [5] If current transformers are available at each end of the windings for the delta-connected generators of Figure 8.7b, the differential relays can be applied for winding protection. [5] As a External ground fault Generator 51G 87GD Phase relays b c R 3 3 3 3 3 3 FIGURE 8.11 Ground (zero-sequence) differential protection for a generator using a directional ground-overcurrent relay. [5]

Where a 2:1 CT ratio is not available, auxiliary CTs can be used. 8.3.3 HIGH-IMPEDANCE VOLTAGE DIFFERENTIAL PROTECTION FOR GENERATORS The high-impedance voltage type of differential protection scheme can be applied as an alternative to the current differential type described. [5] Transmission Line Protection Faults Introduction to System Protection 1 Restricted earth-fault protection function The restricted earth-fault protection function is basically a low-impedance differential protection function based on zero sequence current components. 1 3 1. [4] EHV and HV transformers and autotransformers for volatges above 49.5 kV and MV transformers with rated power above 3-4 MVA have usually as main protection a differential protection for winding faults – short-circuits between turns of a winding or between windings that correspond to phase-to-phase or three-phase type short-circuits. [13] This set of protections is used on HV and MV transformers with rated power above 3-4 MVA as a ” back-up ” protection, in addition to the differential protection. [13] L. The protection scheme is comparatively cheaper than differential protection scheme Restricted earth fault protection is provided in electrical pow er transformer for sensing internal earth fault of the transformer. [4]

It is therefore detected as a fault current by the differential protection even though it is not due to a fault. [13] Sometimes simultaneous faults may occur involving both short-circuit and broken- Differential Protection: Application: Theory and Settings. [4] Differential protection Chapter 10: Symmetrical Components and Unbalanced Faults ordinary circuit theory. [4] This is done through ” differential protection ” (ANSI / IEEE / IEC code 87T), which diagram is shown in Figure 1 and the functioning principle is based in Kirchhoff current law. [13]

Transformer differential therefore requires fairly complex functions as it must be able to measure second and fifth harmonic current or, in order to avoid measuring fifth harmonic currents, it must be able to detect overvoltages of external origin. [13] The SEL-487E transformer differential element is unusual, in that it uses more than just restraint current to select slope 1 or slope 2. [15]

This illustrates and emphasizes that a separate transformer differential relay is recommended for the unit auxiliary transformer(s), as shown in Figure 8.5. [5] Apart from slope 1 / slope 2 selection, testing the SEL-487E is the same as for any other transformer differential relay. [15]

The study of directional overcurrent relay and directional earth-fault protection application for 33 kV underground cable system in Malaysia A. Earth faults within the protection range of both current transformers T1 and T2 result in the addition of the currents. [4] Based on the theory of symmetrical Module 5 : Directional Overcurrent Protection relays are called as directional overcurrent relays [4]

As with all supported relays, the configuration menu lets you configure the relay settings so you don’t have to calculate anything. [15]

Figure 16 shows an example of the connection of the differential protection, using matching auxiliary transformers. [13] If the flux summation CT is not applicable and differential protection is desired, the scheme of Figure 8.7 can be used. 8.3.2 MULTI-CT DIFFERENTIAL PROTECTION (87) FOR ALL SIZE GENERATORS The basic principles of this protection were covered in Section 6.2. [5] The value of Zin is determined by summing the impedances of the earth fault loop described in Section 3. doc Differential protection is to detect phase faults within the TRF on both primary and secondary sides. [4] Restricted earth fault protection ( ANSI/IEEE/IEC code 64G/64REF ) is used as a complement or to replace differential protection for windings faults to earth. [13] The protection scheme is comparatively cheaper than differential protection scheme. [13]

A. Power Equipment 1 KVA 3 phase 415 or 220 Volts alternator coupled to 1.5 HP (Prime mover) with drive unit- 2(Two) sets Resistive load 1-KW for loading the synchronized bus B. Protection RelaysThe Protection Relays incorporated in the Testing Panel should be of ALSTOM / L&T /etc. B1 Over Current Relay Static – 1 No. B2 Earth fault Relay Static – 1 No. B3 Under/Over frequency relay static-1 No B4. [11] The protection relays are used for detecting the faults in the system and to detach the faulty parts from the system in real time. [17] Secondary Current Inject Test requires less current for testing protection relay functionality. [12] The relay is a well known and widely used component. 18, Line protection calculations and setting guidelines for relays installed at kV, kV, kV. [10] In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker. induction; motor operated. Ir is the ratio of the fault current to the relay setting current or a Plug Setting Multiplier. [10] Our relay settings team can perform analysis for equipment change-out, recommend new settings for relay protection in CAPE, ASPEN, and other popular software while verifying the protection system coordination. [18] Setting of the motor protection relay is your motor protective relaying application. [10] Right from simple, basic thermal overload protection, these relays offer precise setting as against the bimetal relays. [10]

This section appears in the dialog box only for those relays which have been entered in the library as generator protection relays. [19] In some cases, for example motor protection relays, they may be called by other names such as Thermal Overload. [19] Comprehensive motor protection relays have been in use for motor protection controllers. [10] Relay MPR is a three-phase LT motor protection relay for motor sizes up to 50KW (max. [10] Execute the installation, testing, commissioning, maintenance and repair work for HV/MV/LV Protection relays etc. in a professional way. [20]

This paper proposes Phasor Measurement Unit (PMU) based adaptive zone settings of distance relays (PAZSD) methodology for protection of multi-terminal transmission lines (MTL). [21] This paper proposed a PMU based methodology for adaptive zone settings of distance relays to improve the performance and reliability of distance protection. [21]

R. Thangaraj, M. Pant, and A. Abraham, “New mutation schemes for differential evolution algorithms and their application to the optimization of directional over-current relay settings,” Applied Mathematics and Computation, vol. 216, no. 2, pp. 532-544, 2010. [17] • % Differential Relay Static Type-with Minimum basic setting Biased feature 10%, 20%, 30%, 40%, 50% setting for Current. [11]

Multi-terminal line differential protection with innovative charging current compensation algorithm. 10th IET international conference on developments in power system protection (DPSP 2010) (pp. 1-5). [21] Gajic et al. have proposed differential protection with innovative charging current compensation algorithm for MTL protection. [21] Al-Fakhri has proposed differential protection methodology against internal and external faults using asynchronous measurements. [21]

POSSIBLY USEFUL

Usually the only way to cause a properly rated generator CT to saturate is for the system contribution of the available fault current to pass through the CT?s primary, and if this happens, the fault is within the generator?s differential zone of protection anyway, so an 87G trip is expected. [8] A particularly crucial situation from the apparent differential current point of view appears at faults just outside the area of protection. [6] The protection operates fast and reliably also for differential current levels just slightly exceeding the set value. [6]

When the protection is implemented using a current relay, the current value at which the relay should operate must be determined first. [6] To obtain as fast and dependable relay operation as possible at faults inside the area of protection, a high- set stage is used in addition to the stabilized stage. [6] As the name implies, this resistor is employed for the prevention of false relay operations on faults outside the area of protection. [6] The measuring principle ensures that the relay operates exclusively on faults inside the area of protection, which means that the protection is absolutely selective. [6]

Now, using fault simulator set R ph HV CT and r ph LV CT current as 1 ampere, now increase gradually any one of the currents Hv or LV and increase till the relay operates. [7] In this situation, the relay must not operate incorrectly and trip the circuit breaker under the influence of the apparent differential current. [6] At the point of operation of relay note the Differential current and restraing current in the measurement of relay, this will be Our Id1 and Ir1 respectively now repeat the same process for HV and LV currents of 1.5 amp. [7]

It is mainly the starting ratio together with the second turning point that determines the operating sensitivity of the relay for internal transformer or machine faults when these objects are loaded. [6] The faults occur in the transformer inside the insulating oil can be detected by Buchholz relay. [3]

With the availability of internal logic equations, the generator relay can now automatically trip the line if the fault clears with the opening of the last generator breaker. [8] StarZ™ transmission and distribution system protection & coordination software offers insight into line protection, protective relay performance & evaluation, troubleshooting false trips, and system-wide protective device operation. [9] The vast majority of the generators in the U.S. Army Corps of Engineers? 75 powerhouses have had their protection systems upgraded from electromechanical to digital multifunction relays that contain new elements and customized logic. [8]

This element is used to detect a ground anywhere on the 13.8kV delta bus connected to the generator, and is the primary protection for phase-to-ground faults. [8] At stabilizing current levels above the second turning point, the high starting ratio secures stability at faults arising outside the area of protection. [6] The protection may respond to a fault current of only a few percent of the rated current. [6] The current transformers used in the high-impedance protection applications must have an adequate accuracy limit factor to be capable of supplying enough current to the relaying circuit on faults inside the area of protection. [6] The design of the stabilization of the high-impedance scheme is based on the assumption that one of the current transformers of the protection fully saturates at faults outside the area of protection, while the rest of the current transformers do not saturate at all. [6] The protection requires class X or PX current transformers according to BS 3938 or IEC 60044-1 respectively, the repetition capability of which is determined by the knee point voltage and the resistance of the secondary circuit. [6] Only if this does not occur, must the transformer be isolated by a special over-excitation protection having a U/f-dependent time delay. [1] The high-impedance principle is particularly well suited for the short-circuit protection of machines, short lines and busbar systems and the earth-fault protection of these and transformers in effectively earthed and low-impedance-earthed networks. [6] To better understand the protection response during short-circuits and switching operations, the physical principles of the transformer are initially covered in detail. [1] In transformer protection applications, the stability is also endangered by a temporary overvoltage. [6]

The large amount of second harmonic in the rush current was already used with conventional protection for this purpose. [1] This current value is needed for the calculation of the overall sensitivity of the protection. [6]

The second turning point also affects the stability of the protection at faults outside the area of protection. [6] NERC Standard PRC-019-2 requires that the over and under voltage trip settings be coordinated with any exciter over/under voltage protection, limiters, and generator limits. [8] If these currents differ from each other as to the amplitude or phase angle or both more than allowed by the setting values of the relay, the relay will trip. [6] Now, apply current greater than the highset setting value with harmonics content, in this condition relay will trip. [7] If the diffrential current upto highset setting value with harmonics content, relay will block tripping. [7] If the inrush current greater than highset setting value, then the relay will picked up & tripped neglecting the harmonics. [7] When the SGF1 setting is selected from the above-mentioned Table, the zero-sequence component in the phase currents will be automatically eliminated.it is in case of ABB relays, for other relays different mechanisms are described in relevant catalogs. [2]

Typically in case of a current relay the stabilizing resistor must be separately installed and connected to the relay circuit. [6] Digital relays do not employ an inverse time versus operate current characteristic as the electromechanical relays did. [8] For relay functions that do not require current above the pre-set value (these can include 24, 32, 64G, & 64F), then the breaker “52a? contact must open within the TD provided. [8] A synchronism checking relay is used to verify that the generator (incoming bus) and system (running bus) frequency, voltage magnitude and phase angle match before allowing the generator breaker to be closed. [8] Typically the generator breaker was set to trip 2 to 4 seconds before tripping the 86 lockout relay which would then shutdown the generator. [8]

At this point it may be appropriate to remove the blocking and to enable the relay to operate in order to prevent too excessive overexcitation of the transformer. [6] The magnetising current at nominal voltage only amounts to approx. 0.2% I n, i.e. in the non-saturated segment of the curve X m is approx. 500 times larger than the nominal impedance of the transformer and approx. 5000 times greater than the leakage reactances. [1] However a current still circulates between the two transformers due to the small damping ( large time constant ? X/R of the windings ). [1] On star delta transformers, these currents are coupled to the non-saturated phase via the delta winding. [1] The magnitude of the differential current caused by the measuring errors and the position of the tap changer is directly proportional to the load current of the transformer. [6] Problems may also arise when the transformer inrush current fed by the protected generator is fairly high compared to the rated current. [6] Please remember at rated Voltage of Transformer, magnetization flux density must be high, now if there is percentage raise in rated voltage due to operational disturbances then there will be the significant increase in magnetization current if this situation persists it will lead to transformer saturation. [2] It must be noted that a similar rush current also arises when a close-in external short-circuit is switched off and the transformer is re-magnetised by the recovery of the voltage. [1] Large rush currents can also occur when asynchronous systems are switched together via a transformer, as the large voltage difference can cause transient saturation of the core. [1] The voltage drop resulting from the initial rush current across the source resistance of the in-feed affects the second transformer in parallel and causes the sympathetic in-rush current (I 2 ). [1] Can you please explain in detail about behavior of distribution lines (medium voltage) when any fault occurs on downstream side or during any transformer charging on downstream side having overhead or underground cables attached with the transformer. [1]

Suppose you have one transformer which has primary rated current I p and secondary current I s. [3] The reason for this is sympathetic in-rush current, which results from the rush current of the transformer that is being energized (Figure 6). [1] When energizing a transformer, one-sided over-excitation results, due to remanance causing large magnetising current flow (in-rush current). [1] On a three-phase transformer, a three-phase rush current will result, which depends on the vector group and the method of star-point earthing on the transformer. [1]

By taking notice of the accuracy limit factors of the CTs, the fault current levels and their supply directions and the sensitivity requirements of the protected object, the setting of the second turning point is in general easily found. [6] By means of the stabilizing voltage and the current setting, the value of the stabilizing resistor is obtained. [6]

This allows to catch blind spots and deep setting errors in the protection system. [9] Reliability standard PRC-019-2 requires that the 24G setting be coordinated with the 24T and excitation V/Hz limiters and protection where installed. [8]

Winding and inter-turn short circuits and earth faults in the windings or elsewhere in the protected area are fault types that call for a sensitive and fast operation of the protection. [6] V/Hz protection is most important during startup, shutdown and manual operation, especially on “unit connected” configurations, because the speed may be less than rated speed. [8] For a fast and dependable operation of the high-set stage, the accuracy limit factor of the current transformers used in the protection must be high enough. [6] The use of intermediate current transformers is not recommended as this increases the requirements set on the main current transformers and lowers the sensitivity of the protection. [6]

The purpose is to provide backup protection for the generator if the primary generator protection, transformer or line relaying fails to activate in a timely manner. [8] One critical case is the switching off of a power station under full load conditions which results in a severe overvoltage condition at the unit transformer as a result of the large excitation of the generator. [1] Where additional connections were made to the delta bus, such as to station service transformer, those breakers were typically set to trip before the generator(s). [8]

Because the impedance of the saturated current transformer is low, a high resistance, that is, the stabilizing resistor, is connected in series with the relay circuit. [6] The obtainable sensitivity depends on the relay type used, the characteristics of the current transformers and the protected object. [6]

This scheme emulates the KLF electromechanical relay and uses an impedance unit, a directional unit, and an undervoltage unit applied at the generator terminals (PTs). [8] This article describes how the Hydroelectric Design Center (HDC), USACE?s National Center of Expertise for hydroelectric power and flood control pumping plant engineering and design, uses national guidance and lessons learned to set main unit protective relays, ensuring USACE assets are properly protected. [8] In response to these events, HDC put together a set of standard 87 settings using a higher minimum pickup than was typically done with electromechanical relays, a dual slope, and harmonic restraint/blocking. [8] As the name implies, the basic setting defines the basic sensitivity of the relay under no-load conditions of the protected object. [6] Open the PTL file from omicron library in of omicron 356 testing kit software and enter all the relevant settings from relay. [7] HDC?s original design recommendation for protective systems in 2003 was for redundant relays with identical settings. [8] Pls send the setting of industrial relay for motor,genrator,busbar,transformer. [6]

The voltage drop formed over the secondary circuit will then be the same as that over the relay circuit, Figure 2. [6] Because the impedance of the relay circuit is high, the secondary voltage may exceed the ratings of the relay and the secondary wiring. [6]

For this reason, a voltage-dependent resistor is to be connected in parallel with the relay in order to limit the voltage to a safe level. [6] In case of a voltage relay, the stabilizing resistor is often integrated into the relay. [6]

Many USACE projects have already upgraded, or are in the process of upgrading, their generator protective relays. [8] This was controversial at the time, given many in the industry believed redundant relays should not be identical due to concerns regarding a single point of failure. [8] This method requires time, effort & knowledge about the measuring algorithm of the relay. [7] While the total outage time with a single relay may be about the same as with a redundant pair, the outage can be scheduled with the redundant relays. [8] It is obvious that redundant relays add to the amount of time required for design, installation and testing. [8] As of the time of writing, DMFRs do not have an inverse time characteristic like the old electromechanical relays. [8] HDC has been replacing any existing breaker failure relays by using a 50BF scheme in the DMFR relay. [8] Modern numerical relays therefore provide an integrated blocking of the trip in the event of over-excitation (over-fluxing). [1] This element only applies to trips initiated by the DFMR. To trip for external conditions, the designer should connect the initiating external devices to a relay input and add that to the logic. [8] To secure the operation of the relay under these circumstances, the activation of the second harmonic-based blocking function is often justifiable. [6] This function, which was already applied in conventional relays, is now available in all numerical relays and may be activated, if desired. [1]

Reverse power relays typically were not originally installed in USACE powerhouses. [8] For units with synchronous condensing, the undervoltage can be added to seal-in the unit run relay when the wicket gates are closed for condensing mode. [8] The field ground relay should be disabled during field flashing. [8] All new protective relay projects designed by HDC make liberal use of test switches to isolate circuits for testing. [8]

HDC uses protection scheme 2 as shown in Figure 4.5.1-3 of IEEE C37.102. [8] If there is an available output from the exciter for field flash monitoring, it can be used as an input to the DMFR to disable the 64F protection during field flashing which would allow a smaller time delay to be used. [8] Therefore the operating time of the protection is very short, typically shorter than one cycle. [6] Two zones of protection using different time delays is recommended. [8]

The U.S. Army Corps of Engineers relies on experience gleaned from its dozens of hydro projects to improve its practices in implementing protection systems for its generators. [8] Other manufacturers compared the 100(120) and 50(60) Hz components directly with a separate bridge circuit, which then directly blocked the protection, as it is now done in the software of numerical protection. [1] This element must be coordinated with the utility prior to implementation to ensure compliance and proper coordination with the utility?s protection scheme. [8] The area of protection is defined as the area between the current-measuring points. [6]

Zone 2 is set to provide backup protection for close-in system faults that aren?t cleared by the bulk power distribution network?s protective relaying. [8] Zone 1 is set to provide backup protection for internal powerhouse faults. [8]

The negative sequence is primarily backup protection for unbalanced system faults that are not adequately cleared, extremely unbalanced load conditions, or an open phase occurs. [8]

The high-set stage operates when the differential current momentarily exceeds the set start value. [6] The second harmonic is filtered out of the differential current (operating current) by means of a filter, and is then used as additional restraint current in the measuring bridge. [1] A low-impedance differential scheme measures the currents on either side of the protected object and forms from these a differential current I d, Figure 1. [6] Test method : Simulate differential and stabilizing currents such that they lie in the first region over and under the curve. [7] The starting ratio caters for the sources of the apparent differential current, which are directly proportional to the through-flowing current. [6] The differential relay compares the incoming phase currents of an object to the outgoing phase currents of the same object. [6] First one is a fixed point, here it is 0.5xIn, it is minimum current sensing point or better we can say for understanding it is differential relay pick up point. [2] To avoid a false operation of the differential relay, the relay must be stabilized, which means that the higher the through-fault current, the higher differential current is required for tripping. [6] An example of the operating characteristic of a stabilized differential relay is shown in Figure 1. [6]

Thanks to its operating principle, the high-impedance differential scheme is particularly easy to implement and set and has a high operational reliability, Figure 2. [6] Now the entire differential current is forced to flow through the secondary circuit of the saturated current transformer, which can be described by short-circuiting the magnetizing reactance X E in Figure 2. [6] Such operations may be caused by the differential current arising from non-simultaneous saturation of the current transformers. [6] The through-fault current is high and may contain a DC-component which may cause saturation of the current transformers resulting in a momentary increase in the differential current. [6]

Transformer diffrential highset setting is given for protecting transformer during starting. [7] The basic setting also affects the level of the entire characteristic curve and thus also the operating sensitivity at higher stabilizing current levels. [6] A more sensitive setting than 15% of the second harmonic should normally not be applied as the off-set short-circuit current will also have a second harmonic component in case of CT saturation. [1] Apply a current less than highset setting with 2 & 5 harmonics content. [7] After calculating the settings, settings curves must be plotted on a P-Q and R-X diagram to coordinate them with the machine?s capability curve, steady-state stability limit, UEL and minimum field current limit curve. [8]

HDC?s recommended settings consisting of a six second time delay when generator terminal voltage exceeds 110% is longer than the standard?s required minimum time delay and thus complies with the standard. [8] NERC Standard PRC-024 Requirement 2 requires that the 59 settings allow voltage ride-through operation within a “no-trip-zone”. [8] The value of the stabilizing resistor is determined according to this voltage setting. [6]

S-setting is the combination of differential pick up and turning point differential setting. [2] The shape of the characteristic is defined by the basic setting, starting ratio and the second turning point, Figure 1. [6] For this setting it must be noted that the 5 th harmonic component again decreases if the over-voltage is very large (Figure 8). [1]

“Loosening” the 87 slope settings would provide more security against false trips, but would have the side effect of covering up problems that should be known. [8] Note that older windings were rated as having a 115% continuous overload capability, therefore the pickup setting would need to account for this. [8] Calculations serve to develop starting points but are not final settings. [8] For calculation of second slope we must know its starting point which is again a value of restraining current. [7] We have to multiply injected currents by amplitude matching factors for calculation of “IIDFF” and “ISTAB”, then we substitute this value of “ISTAB” into characteristic equation, To find Theoretical value of “IIDFF”. [7]

For calculation of the short-circuit current, the resistance may be neglected, it must only be considered when calculating the DC time constant. [1]

The magnetizing current of a saturated power transformer contains a great deal of this particular harmonic. [6] If the transformer is operated with excessively high voltage, then the required magnetization is also increased. [1] If you install CT of ratio I p /1A at the primary side and similarly, CT of ratio I s /1A at the secondary side of the transformer. [3] The transformer can tolerate the over-excitation, which causes heating, for a given time without sustaining damage. [1] “It is usually applied on transformers above approx. 1 MVA. On larger units above approx. 5 MVA it is standard.” [1] The flux does not return to zero when the transformer is switched off, but remains at the remanance point ? Rem, which may be above 80% of the nominal induction. [1] When the transformer is re-energized, the flux increase starts at this point. [1]

This requirement is fulfilled if the k nee point voltage of the current transformers is at least twice the chosen stabilizing voltage. [6] To correct phase shift of current because of star-delta connection of transformer winding in the case of three-phase transformer, the current transformer secondaries should be connected in delta and star as shown here. [3]

During load and short-circuit conditions, a simplified equivalent circuit may therefore be used for the calculations (Figure 2). [1] Under these conditions, a reduced setting of e.g. 12% may be considered. [1] The lower the setting of the second turning point, the better the stability obtained will be. [6] We took two points in setting S- point or starting ratio point. [2]

The connections of the CTs are of type II. The setting of SGF1 has presented in the table above. [2]

The multifunc- tion digital (microprocessor) relays provide many functions in a single pack- age along with digital fault recording, self-checking, and so on. 8.3 STATOR PHASE-FAULT PROTECTION FOR ALL SIZE GENERATORS Phase faults seldom occur, but when they do, large fault currents can flow. [5] Solid neutral earthing means high earth fault currents as this is only limited by the inherent earth fault impedance of the system. 2 A Reference fault protection Basic_Protection_Theory_2013_BW. A relay used in the power system to detect neutral or ground faults measure the vector difference of the three phase power, or measure the neutral restricted earth fault relay principle Sometimes referred to as a Restricted Earth Fault sensing element. [4] The 50 relay provides instantaneous protection, and it must be set above the normal neutral unbalance as well as above the maximum current resulting from primary system ground faults, whichever is greater. [5] An overvoltage relay (59G) is con- nected across the resistor to respond to the V0 voltage for faults in the Gen 50N/51N 50N/51N 51G Gen FIGURE 8.12 Ground-fault protection for ungrounded generators grounded by the connected system. [5] Because the system is otherwise ungrounded, sensitive 3I0 fault detectors in the various circuits connected to the bus can provide location of the fault. 8.8 MULTIPLE GENERATOR UNITS CONNECTED DIRECTLY TO A TRANSFORMER: GROUNDING AND PROTECTION Most often, these are large tandem or cross-compound units operating from a common steam prime-mover source. [5] For this application, the maximum transformer current would be IUAT max load 15,000 ??? 3 p 18 481:13 A at 18 kV (8:16) Thus, a CT ratio of 500:5 could be used for 87UAT, rather than the equivalent 1100:1 ratio required for 87TG. With an equivalent 500:5 (100:1), fault F2 would provide an operating coil current of 5,372.7100 53.73, a good margin for fast and sensitive station transformer fault protection. [5] Primary-Side Transformer Protection Peter J. 1 Earth fault directional protection Input variables In earth fault directional protection, the residual current is measured and the residual voltage is most often used as the polarisation quantity. [4] Stator Earth Fault Protection In most countries, it is a common practice to ground the generator neutral through a Grounding Transformer having a loading resistor across its secondary. 4 Earth Fault Protection The practices used in ground-fault protection are described in a later section of this guide. [4] This neutral or 100% winding ground-fault protection is a relatively new area, so considerable investigation and study are still in progress. 8.7.7 HIGH-VOLTAGE GROUND-FAULT COUPLING CAN PRODUCE V0 IN HIGH-IMPEDANCE-GROUNDING SYSTEMS Ground faults in the primary system produce a voltage in the generator secondary circuit through the primary-to-secondary capacitance of the unit transformer bank. [5]

Using Figure 7.11 as an example, a CT ratio of 400:5 (80:1) would offer I5051 464:38 80 5:80 A (8:17) where the primary fault current in the neutral would be 6.19 A, which would be reflected through the distribution transformer as 464.38 A. These relays must be set higher than the maximum unbalance current that normally flows in the neutral circuit. [5] For this purpose, the earth fault relays are adjusted as to disconnect The earth fault protection scheme consists the earth fault relay, which gives the tripping command to the circuit breaker and hence restricted the fault current. [4] If current is coming up from the ground (or going down to the ground), this protection should o ? perate. b/w restricted earth fault relay & standby earthfault relay and where they a. [4] Earth Fault Currents in Three Phase systems Protection Mechanism and Relays Earth fault occurs when charge flows into the Earth. 4. [4] Ground Fault Monitoring Relays are capable of monitoring ungrounded supplies power systems up to 600V, for maximum equipment protection. voltage on a healthy phase during an earth fault, affecting one or more phases at one point on the system, to the protection task. [4] It would be sized for the fault-limiting as required. 51N50N ground relays connected to the terminal-side CTs provide ground protection for each unit. 51G in the neutral provides ground protection for the trans- former and bus with backup for the 50N51N relays. 8.7.3 GROUND-FAULT PROTECTION FOR UNGROUNDED GENERATORS Ground faults in an ungrounded system (type 3) are easy to detect, but are impossible to locate by relays. [5] For large, important generator units, a combination of (1) and (2) is used by applying two (40) loss-of-field relays. 8.11.2 LOSS OF EXCITATION PROTECTION WITH A VAR-TYPE RELAY A directional power relay connected to operate on inductive vars from the connected system can be applied to detect loss of excitation. [5]

A negative-sequence (46) relay provides protection for unbalanced faults. [5]

Sankaranarayanan and K. We A new terminology for electrical currents now include all faults those between live conductors as well as earth or grounding faults. the fault cleared promptly Directional Overcurrent Relaying (67) Concepts. protection and the residual voltage for directional earthing protection. [4] Therefore, in the power grid, current quick-break protection and instantaneous current quick-break protection are widely used as the main protection of this line to quickly remove faults and use definite-time overcurrent protection as back-up protection for this line and adjacent lines. [14] Therefore, the circuit is equipped with current instantaneous protection and current limit protection after the instantaneous, their joint work can ensure that the fault within the entire line range can be cut within 0.5s time, under normal circumstances can meet the fast-moving Claim. [14]

For the protection of the limit current instantaneous protection in Figure 1, the short-circuit current at the end of the line AB at the end of the line AB in the minimum system operation mode is taken as the calculated value of the fault parameter. [14] This provides protection for both phase- and ground-fault currents as long as the fault level for faults within the differential zone is greater than the sensitivity. [5] Therefore, the protection must be able to distinguish between a differential current due to a fault and a differential inrush current. [13]

When the external fault is removed, the current through the protection 4 and 5 is still in the running load current, due to the voltage drop in the short circuit, substation B bus load on the motor is braked, so in When the voltage is recovered after the fault is removed, the motor must have a self-starting process. [14] Visit us online today Innovative Fault Current Protection Fault Protection and Detection, 10 ? R ON, 4-Channel Multiplexer Data Sheet ADG5404F Rev. Every now and then, accidents phase faults. [4] Visit us online today Innovative Fault Current Protection earth fault is protection component compare difference in voltage between neutral and ground if it’s exceed limited value trip down and disconnect power. [4] We know from theory of symmetrical With the neutral going through the CBCT, the earth fault protection will have No problem irrespective of whether the load what is the diff. earth fault is protection component compare difference in voltage between neutral and ground if it’s exceed limited value trip down and disconnect power. [4] Since the selective current instantaneous protection can not protect the entire length of the line, so we consider adding a new protection to cut off beyond the scope of the fault out of line to protect the full length of the line, But also as a backup current protection protection. [14] The shortcomings of this protection: When the fault is closer to the power supply terminal, the greater the short-circuit current, but the longer the protection action to cut off the fault instead. [14] These protection must be started, but according to the selective requirements, protection 3 should be used to remove the fault and then protect 4 and 5 As the current has decreased, it should be returned immediately. [14] In Fundamentals and Application internal generator fault Generator Protection Types of Generator Grounding 21 Types of Generator Ground Fault Damage The residual current device (rcd) is used to detect earth fault currents and to interrupt supply if an earth current flows. [4] The advantage in using this method of earth fault protection lies in the fact that only one CT core is used in place of three phase CT?s whose secondary windings are currents, the overvoltage between lines and earth, the determination of arrester rating and the system insulation level. 3-phase-to-earth fault, which is the typical fault nature for three phase common tank distribution switchgear. [4] Detection based only on the difference between the transformer primary and secondary currents would cause the protection to be activated. [13] They do this by limiting the current that flows through the neutral point of a transformer to a safe level so as prevent damage to equipment but still operate protection devices. [4] Today, we will discuss about different types of transformer protection and faults in details. [13] Transformers are vital equipment in transmission and distribution network and so the protection against internal and external faults is a very important factor in the design of those networks. [13] With the generators connected to separate transformer windings, each unit must be grounded for ground protection. [5] GEN. 50/51 61 46 Transformer Bus32 or 67 40 87 % 24 59 81 VTs 78 21 or 51V Distribution transformer 59G 50/51 Grounding resistor or alternate resonant grounding Optional 59D or 59 Option location for unit service CT’s 87 TG 87 UAT 4.16 kV Unit service bus Unit auxiliary transformer UAT Optional subharmonic injection 27 52 FIGURE 8.5 Typical protection for a unit generator and for large generators in utility systems. [5] Restricted Earth fault Protection in Transformers & Generators since the objective of the protection is to detect the earth fault in the specific zone Using Broken Delta Protection for Earth Faults The Broken Delta configuration is used to protect against earth faults. [4] Residual voltage transformer (RVT): RVTs are used for residual earth fault protection and for discharging capacitor banks. [4] Theory This is especially true for earth fault impedance measurement, where the arc protection scheme for fast earth fault protection in medium and high voltage networks. 2 General information about MV/LV transformers The transformer is the most important part of the transformer substation. [4]

GET-8390: Sensitive Ground Fault Protection in the F60 2 GE Power Management Typical Connections for Ground Fault Protection RESIDUAL CONNECTION The ground fault elements are connected in the common neutral connection of the line 46 Transformer Protection Principles 4. [4] In the UK Standby earth fault protection is widely applied to transformer neutral connections to provide back up to bus zone protection, uncleared feeder earth faults, faults not within the REF protected zone, and uncleared faults in the REF protected zone. – Earth Fault Detection: Basics in Theory Version 1. [4] Technical Bulletin 18, Version 4 Date: November 2011 Page 3 of 12 Introduction Restricted earth fault protection provides earth fault protection for the secondary side of the transformer and Fault detection is confined to the zone between the two CTs hence the name ‘Restricted Earth Fault’. 4 Final Exams they are not trying to go into the earth. [4]

Bakar, H. Restricted Earth Fault Protection of Generator Generally Merz-Price protection based on circulating current principle provides the protection against internal earth faults. [4] Rating & Testing Neutral Grounding Resistors the connection of earth ground to non-current carrying ? Improved system and equipment fault protection Basic Theory, develops the principles of personnel protection, fault protection, lightning protection, interference reduction, and EMP protection for C-E facilities. [4] The earth-fault protection by relay in neutral to earth circuit depends upon the type of neutral Earthing. [4] Inverse-time-instantaneous overcurrent (5051) relays in the resistor sec- ondary circuit (Figure 8.5) provide alternative or backup ground protection. [5] Suppose only one unit is grounded, if a ground fault occurs in that grounded unit, a 51G relay (as shown in Figure 8.3) will provide protection. [5] The individual protection units shown in Figure 8.3 and Figure 8.5 may be separate relays or may be combined in various combinations. [5]

Generator thermal capability curves Var loss-of-field Relay operate area 0.75 +P 88 +jQ ?jQ -P ?0.4 ?0.6 IGen lagging IGen leading FIGURE 8.18 Loss of excitation protection with a var-type relay. [5] Introduction 31 9. 2 Isolatedsystem 2014 Western Protective Relay Conference 64S Protection Guide? Theory, Application and Commissioning of Generator 100% Stator Ground Fault Protection what is the diff. [4] Where the generator has resistance temperature detectors (RTDs) within the windings, additional protection can be provided by a bridge network relay. [5] The relay senses the earth faults beyond the transformer/generator winding hence such protection is called unrestricted earth-fault protection. e. [4] To give priority to ensuring the selectivity of relay protection, it is necessary to set the starting parameters of the protection device to ensure that the next line exit at a short circuit does not start, which in relay protection technology, also known as escape by the next line exit Department of short-circuit conditions set. [14]

After that short time the currents will ramp in Fault 2, and the relay should operate when the Id/Ir point passes the slope 2 line. [15] Press FAULT. Fault 1 currents will be generated for a short time, which should not cause the relay to operate. [15]

Because these relays are nondirectional, they must be coordinated with upstream devices for which the small generators can supply fault current. [5] The operation for Negative Sequence currents The negative sequence current I flow in the primary winding of the relay because of the fault current. [16] A 0.2 sec time delay is recommended to prevent operation on transient conditions. 8.12 GENERATOR PROTECTION FOR SYSTEM DISTURBANCES AND OPERATIONAL HAZARDS In the previous sections the discussion has covered primary protection for faults in the generators and backup protection for uncleared or delayed faults using relays 21, 46, and 51V. Loss of excitation (40) may be caused by a rotor field fault or by inadvertent tripping of the field. [5] F. Chong Introduction One of the main objectives of most utilities is to provide secure and reliable supply to their Relay Theory and Basic System Protection. do not offer the same level of personal protection against faults involving provide backup protection for system faults when the power system to which the generator is connected is protected by time-overcurrent protections. [4]

One protection scheme connects an undervoltage relay (27) respon- sive to third harmonics in parallel with 59G as shown in Figure 8.5. [5] Definite-time Overcurrent Relay EARTH FAULT AND PHASE FAULT PROTECTION Earth fault relay and over current relay Earth fault Protective schemes 33. [4] This reference variable is called the polarisation quantity. detect phase faults clear of earth is an advantage, although the phase fault sensitivity need not be very high. 3 CALCULATION OF ESDD-02-006 a single phase to earth fault may result in more Over current Protection Schemes (2). [4]

In this way, when d1 is short-circuited, protection 2, 3, 4, and 5 may start under the action of short-circuit current, but to meet the selective requirements, only protection 1 action should be taken to cut off the fault and other protection should be immediately after the fault removal return. [14] Generally, the 51V overcurrent unit is connected to one phase with a phase-to-phase voltage for three-phase fault protection. [5] This scheme may offer limited protection when the normal full-load third- harmonic voltage is high, and time coordination is used to avoid operation for higher third-harmonic voltage during external faults. [5] As shown in Figure 2 (a), we can call it a fast-limiting current-trip protection because it can quickly cut down the fault within the entire line range with a small time limit. [14] It is thus detected by the protection as a differential current and it lasts far longer than the protection operating time ( 30 ms ). [13] Generator RC R R (a) (b) OP OP OP R R R R RC a b c a b c Ia Ia Ib Ic IA RC RC IC IA – IB IB – IC IC – IA R OP OP OP R R R R R IB Ib Ic Ia Ib Ic IA – IB Ia IB – IC Ib IC -IA IC Ia IA – IB Ib IB – IC Ic IC – IA FIGURE 8.7 Typical differential (87) connections for the protection of wye- and delta- connected generators: (a) wye-connected generator; (b) delta-connected generator. [5] As indicated in Chapter 6, the best protection is differential (87); consequently, this type is recommended for all generators, except possibly for small units of 1 MVA and less. [5]

This protection is a backup primarily for unbalanced system faults that are not adequately cleared; but it also backs up the protection for the generator unit and associated equipment. 8.7 STATOR GROUND-FAULT PROTECTION Insulation failure is the major cause of most faults in a generator. [5] Unlike phase and neutral overcurrent protection, the key advantage of distance protection is that its fault coverage of the protected circuit is virtually independent of source impedance variations. [4] REF protection is fast and can isolate winding faults extremely quickly, thereby limiting damage and consequent repair costs. control circuit for two overcurrent and one earth-fault 5. [4]

When the primary current of the line to be protected reaches the value of the starting current, the protection 1 installed at the A-bus can start up and finally acts on the protection circuit 2 of the circuit breaker 1. [14] A residual current operated circuit breaker designed to perform the functions of protection against earth fault currents, overloads and short-circuits. [4] The current may be high enough to operate the over current protection fuse or circuit breaker, which will then interrupt the circuit. [4] Basic Electrical Theory ? ESTABLISH REFERENCE TO EARTH – Allows for Protection devices to operate ? Returns fault current to SOURCE, NOT EARTH Ground Fault Protection. [4] Behind the paragraphs of the current line speed breaking protection setting principle Ibid. [14] Now take the protection 1 in Fig. 2 as the example, to explain the setting method of the instantaneous current breaking protection. [14] For these applications, the unbalance oper- ation should be supervised by a zero-sequence voltage level detector, or a higher setting used. 8.12.5 THERMAL OVERLOAD (49) The generator control system usually provides protection from overloads. [5]

The operating time can be approximately 2 sec. 8.12.2 OVEREXCITATION: VOLTS PER HERTZ PROTECTION (24) Generators as well as transformers must not be subject to overvoltage except for short or transient excursions. [5] T1 is the operation time of No. 1 (motor) protection; t2 is the operation time of No. 2 (transformer) protection; t3 is the operation time of No. 3 (line BC) protection. [14] During internal fault the neutral current transformer only carries the unbalance fault current and operation of the protection takes place. [13] P a g e Negative sequence protection, Earth fault detection in rotor circuit Power transformer Protection: Biased The type of earth Fault protection that has to be provided will depend upon the type of Neutral grounding provided for the generator. [4]

Grounding Transformer FAQs. 3: Earth-fault current directions (Siemens; Siemens, 2008). the fault cleared promptly I. The relay senses earth fult current by its Neutral Grounding Resistors. 1 General aspects The loss of insulation between normally live conductors and exposed-conductive-parts may generate a fault, which is generally called earth fault. [4] MV transformers with rated power up to 2.5 MVA are usually only protected against overcurrents using over current relays. [13]

Meyer, S&C Electric Company, Chicago, Illinois Faults in this area cannot usually be detected by the relay The current carrying capability of the grounding conductor is coordinated with the overcurrent device of the electrical supply system. [4] 59G relays should have a time delay to permit the primary ground relays to clear high-side faults if the coupling voltage is greater than the 59G relay pickup. [5] The CT primary rating should be about one-half of the maximum ground-fault current with the 51G set at approximately 0.5 A. Time coordination is necessary with other ground relays that may be overreached. [5] The National Electrical Code (NEC ) has specific ground fault An earth fault relay, connected to the secondary winding, is energised only when there is residual current in the primary system. [4] The current coil of earth-fault relay is connected either in neutral to ground circuit or in residually connected secondary CT circuit. [4] The secondary CT ratio is selected to give approximately the same relay current as that flowing in the generator neutral for a ground fault. [5]

On the basis of current normally flowing out of the generator into the power system, the relay characteristics and connections should provide an operating zone from about 308-608 through 1808 (reverse power into the generator) to 2108-2408 lead. [5] The generator current will move into the leading area (vars from system) to operate the var relay as shown. [5] For the external fault F1 as shown, the currents through the restraining windings of the differential relay would only be the contribution from the generator, which is I1F1gen 50,357:3 0:485 1,100 22:2 A sec (8:12) This would be the internal and total fault current if a three-phase fault occurred before the units were synchronized to the 345 kV system. [5] Because there is no breaker between the generator and the transformer, this differential is connected to include the generator, for both the units must be tripped for either transformer or generator faults. [5] In Figure 8.5, the high-side CTs on the unit auxiliary transformer should be included in the 87TG differential, so that faults in the unit auxiliary transformer (UAT) and 4.16 kV system are external. [5]

Voltage is from the generator voltage transformers (VTs) and is used to prevent the time- overcurrent unit from operating, until a fault decreases the voltage. [5] This is a complex phenomenon and beyond the scope of this book, particularly as it occurs only in a few systems with series capacitance. 8.13 LOSS OF VOLTAGE TRANSFORMER SIGNAL Signals from VTs connected to the output terminals of generators are used to supply associated protective relays and voltage regulating equipment. [5] As an alternative, or supplement to 51G, a voltage relay (59G) can be applied. 59G is connected inside the delta of a wye (grounded)-delta auxiliary transformer supplied from VTs connected to the generator terminals. [5]

An external fault in the star side will result in current flowing in the line current transformer of the affected phase and at the same time a balancing current flows in the neutral current transformer, hence the resultant current in the relay is therefore zero. [13] The relay will not response even there is an unbalancing in phase current of the power transformer. [13] When using a three-phase type 21 relay, the phase shift of the transformer does not affect the reach, as it does for single-phase-type units. [5] The phase R energized the upper half of the relay by the help of CTs and auxiliary transformer while the lower half is energized by the phase Y. The auxiliary transformer is so adjusted that their output is lagged by an angle of 120 instead of 180. [16]

Instead of tripping the faulty feeder, the Ground Fault Neutralizer cancels out the fault current by injection of an anti-phase High resistance grounding of the neutral limits the ground fault current to a very low level (typically from 1 to10 amps) and this is achieved by connecting a current limiting resistor between the neutral of the transformer secondary and the earth ground and is used on low voltage systems of 600 volts or less, under 3000 amp. [4] Zrelay kV2 Rc MVA Rv Zpu secondary V (8:20) Rc and Rv are the respective current and voltage transformer ratios used for the distance relay. [5]

Experience has shown that the inrush current wave contains at least 20% of second harmonic components ( current at a frequency of 100 Hz ), while this percentage is never higher than 5% upon occurrence of an overcurrent due to a fault inside the transformer. [13] This provides high- speed backup only for the unit transformer and generator, but not for the connected system. 8.6 NEGATIVE-SEQUENCE CURRENT BACKUP PROTECTION Negative sequence in a generator crosses the air gap and appears in the rotor or field as a double-frequency current. [5] Low-side unit auxiliary transformer CTs could be used so that the UAT is within the 87TG protection zone. [5] The thermal overload protection function may be used to protect equipment with two operating rates, for example transformers with two ventilation modes, with or without forced ventilation ( ONAN / ONAF ). [13] This video shows the practical demonstration of protection system for the transformer with the highest sensitivity towards the earth fault. [4] Where protection schemes use the grounding transformer for Electrical Protection. [4] MV/LV transformer substations: theory and examples of short protection device which remains installed at the beginning of the line. [4] Transformers are provided with bullet on ( internal protections) for dielectric failure ( formation of gas ), temperature, oil pressure, level, winding temperature and on load tap changer. [13] We have already discussed about it in detail in our previous post ” Transformers Fire Protection System – Causes, Types & Requirements “. [13] It is important to recognize that including the UAT in either the 87TG or 87T zones usually does not provide good or adequate protection for the transformer. [5] In these situations the switch-disconnectors must have a tripping coil to allow the action of the built-on protections of transformers. [13]

Earth fault protection is protection based on ground, or zero sequence current. [4] Pickup with zero sequence current can be much below the load current value, thereby providing sensitive earth fault protection. [4] A ground-fault protection of equipment device is intended to The main disadvantage of the distance protection is that its inability to sense the earth fault with very low fault current. [4] To avoid earth fault current, a protection is implemented by professionals. [4] Restricted earth fault protection theory pdf Visit us online today Innovative Fault Current Protection Solutions from TE Connectivity. [4] It is assumed that a short circuit occurs at some point of the BC line (for example, point d2), which is within the range of the instantaneous current quick-break protection of the protection 1 in addition to the instantaneous instantaneous current protection and the quick-, It is assumed that the protection of current 2 of protection 2 can not be operated for various reasons. [14] In order to be able to protect the full length of the line, the current limit protection must be the minimum operating mode of the system, the end of the line short circuit occurs when the two-phase, with sufficient response capacity, this capacity is usually sensitive coefficient to measure. [14] Assuming that each line is equipped with current-breaking protection, for the protection 1 installed at the A-bus, the starting current must be set greater than the short-circuit at point d2. [14] The protection gives a trip order when the heat rise E, calculated according to the measurement of an equivalent current I eq, is greater than the set point E s. [13] Set the protection 2 is equipped with instantaneous current protection, the starting current calculated in accordance with (1-3) is: Assuming the protection range of B bus to d3 between the part, then the short circuit occurs at d3, the short circuit current is, Protection 2 quick-break protection just to move. [14] Are equipped with overcurrent protection, the protection of the starting current are in accordance with the protection of the components are to avoid the maximum load current to set. [14] As the current fast-break protection can not protect the full length of the line, and the limit of the current fast-break protection can not be completely as the backup of adjacent lines of protection, therefore, in order to ensure rapid and selective cut-off, often the current instantaneous protection, Time-limiting current protection and timing overcurrent protection combined together to form a phase-type current protection. [14] Operation proved that the protection of the current instantaneous protection is probably the line of 85% to 90%. [14] When the relay?s or instrument transformer?s perform- ance is impaired at these low frequencies, supplemental temporary protection should be provided. 8.11 REDUCED OR LOST EXCITATION PROTECTION (40) 8.11.1 LOSS OF EXCITATION PROTECTION WITH DISTANCE (21) RELAYS Protection to avoid unstable operation, potential loss of synchronism, and possible damage is important and is applied for all synchronous machines. [5] If they are not supplied, or if additional protection is desired, protective relays are available. [5]

After the time limit of the protection 2 is determined, when the d2 point is short-circuited, it will cut off the fault by the time t2. [14] To study the principles of distance protection. nz The micro controller based motor protection system combines control, monitoring and protection function of induction motor from incipient faults in one assembly. [4] GROUND FAULT PROTECTION A Ground Fault Detection and Protection method II. (b) Fault current magnitude as a function of fault location. [4] Protection against phase to ground faults can be a difficult problem since ground fault currents vary within a large range, becoming almost negligible in some situations. [4]

Additional protection for this is provided by three-directional, inverse-time-overcurrent units (67), one in each phase, connected to operate for reverse power into the generator. [5] The protected area is not restricted to the transformer/generator winding alone. installed improperly – ground loops around buildings and interconnecting buildings are not enough – the ground conductor must be run in a conduit with the phase conductors (ground conductors act as an inductor when outside of the conduit). 3 & Ch. 2008 – Generator Protection Earth Fault Detection Earth_Fault_Detection_20110214. [4] Grounding Theory Ebooks, Ground Fault Protection Schemes Books Distributor India Grounding theory and ground fault protection schemes Ground fault protection Earth fault protection is one of the most widely used protection systems. [4] If resonant grounding is used for the generator, the primary ground fault may also affect the protection system. [5] This provides sensitive protection to phase faults, but may not provide ground fault protection, depending on the type of grounding used, as covered in Chapter 7. [5] Earth-Fault Protection in Systems with Isolated Star Point Fig. In addition, the basic theories of earth Advantages and Disadvantages of Different Types of Neutral Grounding conducting body that serves in place of earth. voltages are affected. [4] The secondary residual voltage winding is 3. ppt What You Don?t Know About Ground Fault Protection Can Negatively Affect or earth. [4]

As shown in Figure 3, when d1 is short-circuited, the short-circuit current will flow through protection 5, 4, 3. [14] In normal operating conditions, this magnetizing current is very low and does not reach the protection operating threshold. [13] The main advantages of current breaking protection are: simple and reliable, fast action, which has been widely used. [14] If the current instantaneous protection of the protection 2 encounters a negative error, its protection scope is smaller than the calculated value, However, the positive current limit protection of protection 1 has a positive error and its protection range is larger than the calculated value. [14] Over-current protection is usually refers to the starting current to avoid the maximum load current to set a protection. [14] For current protection that responds instantaneously to current increases, it is called current trip protection. [14] We Advanced protection systems against earth fault: all the information you may need about the normative aspects of protection against earth fault and indirect contact (definition, types of distribution systems and prescriptions as regards the protection of human beings), ABB solutions (from RCDs to electronic trip units), and how to obtain Power Cable Protection in Transmission System Student: Zhihan Xu topology, and fault conditions. [4] Earth fault protection responds to single line to ground faults and double line to ground faults. 5) Earth-fault protection by earth-fault-relay connected REVIEW OF GROUND FAULT PROTECTION METHODS FOR GROUNDED, UNGROUNDED, AND COMPENSATED system neutrals connected to earth (or ground fault protection for solidly Earth fault protection 9. [4] This scheme does not provide protection to the connections from the flux summation CT to the generator breaker, unless the CT is on the bus side of the breaker and the generator neutral side leads are carried to that point. [5] It is widely used to provide fast and very sensitive protection to the generator and associated circuits. [5] Where two high-side generator breakers are used, as in a ring or breaker and half buses, there can be enough normal unbalance circulating in the bus to operate this sensitive protection. [5] This protection is not possible to operate if the small generator is ungrounded and if it is not connected to the large system. [5]

Mokhlis, H. Protection shall have adequate sensitivity to detect faults, considering a single system contingency or fault resistance which results in reduced operating quantities to the protection. [4] Ground-fault protection is very important, although fortunately, such faults are relatively rare. [5] Basic Theory, develops the principles of personnel protection, fault protection, lightning protection, interference reduction, and EMP protection for C-E facilities. [4]

In the above formula can take two current equal? If chosen equal, it means that the protection of the limited current instantaneous protection range of 1 and the protection of the current instantaneous range of protection coincide, which in the ideal case is possible, but in practice is not acceptable. [14] For the reliability factor: Considering the short-circuit current in the non-periodic components have been decayed, it can be selected than the current quick-break protection is smaller, generally taken. [14] For the limit current quick-break protection should be required. [14] According to the requirements of selectivity, the protection outlet of protection 2 should be tripped by the current limit of protection 2. [14]

In Fault 1, set the winding currents so that the restraint current times ?2 is higher than DIRTR and the differential current times ?2 is less than DIOPR. The differential current must also be below the slope 2 line. [15] The differential and restraint current readouts, and the point on the characteristic graph, are calculated from the compensated negative sequence currents, as they are in the relay. [15] The current setting value of the relay is kept less than the normal full load rating current because the small overload current can cause the serious conditions. [16] The relay always has a low current setting because the small magnitude overcurrent can cause dangerous situations. [16] There are some miminimum current requirement for the distance relay to start the zone measurement and if the fault current is lees than this setting. [4]

With maximum- operating energy with the two currents in phase, the relay will operate with higher currents out of phase +908 and with different magnitudes as long as the product times the cosine of the angle between the currents is greater than the tap product. [5] The operation for Positive Sequence Currents The current I R and I Y flow through the primary windings of the relay. [16] Stator current through the relay produces replica temperatures to operate when they are in excess. 8.12.6 OFF-FREQUENCY OPERATION Steam turbine blades are designed and tuned for efficient operation at a rated frequency rotation. [5] When you apply those currents, the relay will enter high security mode, so it will not trip immediately even if the initial point is above the slope 1 line. [15] Ground relays may also be used if the large system can supply ground fault current. [5] The voltage-controlled type with an adjustable fixed pickup, typically 50% of rated current, is easier to set and coordinate with other relays. [5] Relay sensitivities (pickup current) are near 0.14-0.18 A for the 10% and variable percentage types and about 0.50 A for the 25% types. [5]

The negative sequence relay protects the generator and motor from the unbalanced load which mainly occurs because of the phase-to-phase faults. [16] For phase to phase faults the relays in only the affected phases operate. [4] For most relays, this 4.88 A is probably above its minimum pickup, but the low value of fault provides very low multiples of pickup and marginal sensitivity. [5] The relay may enter high security mode when the currents step to the prefault values, but it will exit high security mode 60 cycles later. [15] The current I Y flows through the operating coils of the relay. [16] All these schemes require specific data for the third-harmonic voltages over the operating ranges of the generator, for both the real and the reactive power, before the relays can be set properly. [5] These two types are in wide use, with 51V generally applied to medium and smaller generators, and 21 for large-unit generators. 8.5.1 VOLTAGE-CONTROLLED OR VOLTAGE-RESTRAINT TIME-OVERCURRENT (51V) BACKUP PROTECTION This is a nondirectional relay; therefore, it can be connected to CTs at the terminal as in Figure 8.3 or at the neutral end as in Figure 8.5. [5] The 51V must be time- coordinated with any system relays it can overreach. 8.5.2 PHASE-DISTANCE (21) BACKUP PROTECTION On large generators, especially the unit types, phase-fault backup is usually provided by phase-distance units (21). [5] Only one negative- sequence (46) and one distance (21) or three-phase (51V) relay for backup protection are necessary, and they can be connected to either unit. [5]

For units with brushes, a relay (64) with a voltage-divider circuit can be connected across the field and the exciter with a sensitive DC-type relay that is connected between bridge network and ground. [5] When a ground occurs in the field of exciter circuits, a voltage appears across the relay to produce operation. [5] Wherever applicable, an undervoltage unit set to drop out between 87 and 80% of normal voltage is used to supervise the relay operation. [5] When a ground fault occurs near the generator neutral the third-harmonic voltage is shorted out, or is significantly reduced to dropout the 27 relay, thus closing its contacts. [5] The power directional relay is connected to operate when real power flows into the generator. [5]

With a ratio of 18:240 kV, relay 59G receives 17.24 V. This is above the pickup, so the relay would receive operating energy until the 345 kV fault is cleared. [5] Flammable gas found in the relay indicates some internal fault such as overheating or arcing, whereas air found in the relay may only indicate low oil level or a leak. [13]

In delta connection no zero sequence current flows through the relay. [16] This limits the phase-to-ground faults to just over 400 A. For an internal ground fault at F, I0g 400 200 2:0 A through the operating coil (8:5) With the 87 phase relays set to operate at 0.4 A, the solid ground fault of 2.0 A is five times the relay pickup. [5] When it is set such that it looks into the system, a fixed timer provides the necessary time delay to coordinate with all the relays its setting overreaches. [5] The 59G relay with pickup values from 1 to 16 V provides good sensitivity, protecting approximately 90-95% of generator windings. [5]

They should have identical char- acteristics, negligible leakage reactance, and fully distributed secondary windings. 8.3.4 DIRECT-CONNECTED GENERATOR CURRENT DIFFERENTIAL EXAMPLE A 20 MVA generator is connected to a 115 kV power system, as shown in Figure 8.9. [5] For this fault the total positive-sequence reactance of the system plus the transformer is X1F2 0:064 0:08 100 15 0:064 0:533 0:597 pu (8:14) I1F2 IaF2 1:0 0:597 1:675 pu 1:675 3207:5 5372:7 A at 18 kV (8:15) In the overall differential, the equivalent CT ratio will be basically close to 1100:1, therefore, with this ratio, the fault F2 will be 5372.71,100 4.88 A secondary. [5] In large generator units, an additional differential 87T is sometimes connected around the transformer. [5]

Typical sensitivities provide operation if one phase current is less than 20-60 mA and the other above 40-200 mA. These are in the primary or high-voltage side of the unit transformer. [5] The primary and secondary currents have different amplitudes owing to the transformation ratio and different phases depending on the coupling method (delta-star transformer makes a phase displacement of 30). [13] The magnetizing current constitutes a difference between the transformer primary and secondary currents. [13]

Figure 8.15b shows the calculation for a primary V0 fault voltage of 81,467 V, which reflects through the interwinding capaci- tance to produce 1,293 V across the grounding distribution transformer pri- mary. [5] Calculation of the currents for a phase-a-to-ground fault on the primary 345 kV bus is shown in Figure 8.15a. [5]

Reply MV/LV transformer substations: theory and examples of short-circuit calculation 5 mation on MV/L mer substations 1. between the conductors and the earth (charging current of the system). [4] With normal operation near the knee of the iron saturation curve, small overvoltages result in significant exciting currents in transformers, and excessive flux densities and abnormal flux patterns in generators. [5] In case of large generators, voltage transformer is connected between neutral and earth (Fig. Construction & Theory of Operation. [4] A good method is to ground the main transformer as shown in Figure 8.12, or if this transformer is delta on the generator side, to provide a separate grounding wye-delta transformer connected to the bus and used only for grounding. [5] This protection is connected to current transformers CT (Current Transformers ) at both side of the transformer ( primary and secondary ), as it was shown in Figure 1. [13] Core Balance Current Transformers (CBCT?s) are employed for providing earth leakage protection in a power system. [4] This scheme of restricted earth fault protection is very sensitive for internal earth fault of electrical power transformer. [13] For large generators, as there are costly, an additional protection scheme called restricted earth fault protection is provided. [4] Protection requires Sensitive Earth fault Protection scheme is used for the detection of earth fault. [4] They are different from normal protective Sensitive Earth Fault protection is required to either to alarm or trip the faulted circuit. 6 A practical guide to earth resistance testing The possibility exists that a fault in the power system will cause a high cathodic protection. [4] Restricted Earth-Fault Protection Earth Fault Short Circuit vs. It covers only the protection of restricted regions like windings,breakers & cables. [4] CLASSIC THEORY For three phase AC powered loads, three separate EPSY – Earth-Fault Protection System The Earth Fault Detection Device (EFD 500) provides reliable and selective detection of high impedance earthfaults in resonant grounded networks. [4] The effect is difficult to give in text. 1 Transientearth-faultrelay7SN60 Fig. Directional / non Directional Directional / non Directional Overcurrent Protection P120 Phase II V11 and earth fault protection. [4]

The generator voltage is proportional to frequency and the magnetic flux, so overvoltage protection should have a constant pickup as a function of the ratio of voltage to frequency, a volts-hertz (24) type. [5] The function and protection of these and other protective units that can be applied on generators are described in the following sections. [5] Grounding only one of the generators with an ungrounded system pro- vides the liability of operating as ungrounded when that unit is removed from service either manually or through its protection. [5] These changes have not altered the basic requirements needed to provide good protection for the generator units themselves. [5] Smaller generators, common among DG, warrant less sophisticated protection, however, as their cost is significantly less than large units. [5] Separate generator protection should be applied to each generator unit. [5] The information provided in this chapter covers protection requirements for generators in general and for special protection that may be required in some instances at the point of generatorpower system inter- connection. 8.1.1 HISTORICAL PERSPECTIVES When the electric power industry first developed at the turn of the twentieth century, it was characterized by small companies that operated small gener- ators in municipal areas. [5] A typical illustration of protection for the unit-connected generator is shown in Figure 8.5. [5] The 67 units are shown in Figure 8.5. 8.12.4 BREAKER POLE FLASHOVER (61) Where there is the potential for a pole flashover before synchronizing or after separation from the power system, additional pole disagreement protection is recommended. [5] If one unit can be operated with the other shut down, each unit should have complete protection, as outlined and summarized earlier in Figure 8.5. 8.9 FIELD GROUND PROTECTION (64) Ground detection for the exciter and field are important and usually supplied as part of that equipment, rather than applied by the user. [5] Ground faults in either unit will operate the ground protection as discussed earlier. [5]

Where the differential does not provide protection, the 51G is the primary ground-fault protection. [5] 18) generator protection intertie protection for distributed generati? Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. [5] The intertie protection protects the utility system, to which the generator is connected, from harm caused by the generating facility. [5] The utility will also usually require test documentation to assure that the intertie protection is properly constructed, set, and maintained, as the reliability and safety of its system are at stake. 8.2 GENERATOR CONNECTIONS AND OVERVIEW OF TYPICAL PROTECTION Some common connections for generators are as follows: 1. [5] Generator breaker failure In the case of DG, additional protection is required at the location where the generator is interconnected to the system. [5] This protection also serves to protect the generator from events that may originate on the utility power system. [5] Based on the theory of symmetrical Power System Protection Manual Note: 4. the resistance of the earth limits 06 System Grounding Introduction to System Protection Protection Basics and Terminology. [4] Transmission Line Protection Faults Introduction to System Protection Directional Earth Fault Protection for Transmission Lines – Need and Operational Experiences V. ? Selectivity Protection systems should remove from service the minimum number of system elements necessary to clear a fault. [4] Restricted earth fault is to detect earth faults in the zone from secondary winding to Earth fault protection 9. [4] The restricted earth fault protection is connected in this close path. [13] If no inhibiting mechanism is provided, the Restricted earth fault protection scheme is designed to respond to earth faults in particular zone i. [4] These schemes provide the possibility of 100% winding protection and monitoring capability. [5] Additional protection is required for ground faults that may occur near the neutral end of the stator winding. [5] Answer / hari REF is a kind of protection that is connected to the Star Wnding CT which has a neutral connection. [4] Then 51G in the grounded neutrals provides backup or “”last resort?? protection, which may be nonselective. [5]

Application of overfrequency relaying for turbine blade protection is not critical as generator controls can be usually relied on to run back generator output to achieve the required reduction in frequency. [5] For these systems, out-of-step protection at the generator must be added, for none of the other protection can respond adequately. [5]

Lightning protection of power transformers is achieved by surge arresters installed in the transformer tank, as shown in Figure 5. [13] The most common function provided for thermal protection of power transformers is the thermal overload (ANSI/IEEE/IEC code 49 ) function. [13]

When an overvoltage occurs outside the transformer, the magnetic material saturates (in general the transformers are dimensioned to be able to operate at saturation limit for the nominal supply voltage ), and the magnetizing current value greatly increases. [13] When one side of the transformer is star-connected with an earthed neutral, the matching transformers on this side are delta-connected, so that the residual currents that would be detected upon occurrence of an earth fault outside the transformer are cleared. [13] The injection of subharmonic frequency current can be by a separate neutral transformer or through the broken-delta VT connection. [5] Transformer switching causes a very high transient current ( from 8 to 15 I n ), which only flows through the primary winding and lasts several tenths of a second. [13] All faults in transformer core and windings result in the localized heating and breakdown of o il. [13] Overheating in transformer may be caused by overloads above the permissible overloads specified by the manufacturers, according to IEC Standards ( 60354 for oil-filled transformers and 60905 for dry type transformers ), and external faults, such as short-circuits on installations downstream. [13] Transformer faults may occur in the oil due to gas formation, ageing, contamination with air and lack of level and pressure. [13] Most of these faults may be limited by proper maintenance of a transformer. [13] The fault duration is a critical parameter for the transformer designer. [4] The connections and relays for transformers are discussed in Chapter 9. [5] Buccholz relay has multiple methods to detect a failing transformer. [13] The 87 relays are connected to two sets of current transformers; one set in the neutral leads, the other in the line side. [5] In this module we will show how the earth fault relay works and how it can be connected to the current transformers to generate the current information that we need. [4] Figs. The earth fault currents that operate an rcd can range Page 1 EL731 AC/DC Sensitive Earth-Leakage Relay Rev. a-Earth fault inside the protected zone b-Earth fault outside the protected zone Fig. As illustrated in IEC60044-1, the class X current transformer is needed. [4]

An earth fault relay detects earth faults, or conditions where live conductors come in electrical contact with the system ground or neutral. [4] Another possibility is to apply sensitive ground directional relays set such that it looks into the generator, at the terminals of the generators. [5] Its usual closed contact is in series with a voltage-sensing (59) relay connected to the generator VTs. [5] The relay operating coil is connected to the midpoint of the circuit as shown in the figure below. [16] The relay in this case operates to transmit impulses to trip the circuit breakers at both ends of the faulted line. [4] This is much more numerically complicated than the single- (usually earth or The grounding system appears to the lightning impulse as a transmission line where wave propagation theory applies. restricted earth fault relay principle Sometimes referred to as a Restricted Earth Fault sensing element. [4] The negative sequence relay has earthing which protects them from phase to earth fault but not from phase to phase fault. [16] The relays are connected between phase and neutral leads of the paralleled CTs. [5]

Another scheme applies an overvoltage 59 relay that is responsive to the third harmonics across the broken delta generator VTs. [5] Typical relay sensitiv- ities with microprocessor relays are as low as 1 mA, which may be required when a generator can operate with partial prime-mover input. [5] With low-impedance grounding and sufficient current to operate the differential relays of the generator and bus, proper minimum isolation can be achieved. [5] Normally, if the differential relay used, it will detect the fault and it operates and safeguards the device. [4] The differential relays should have good immunity to avoid incorrect operation on an external fault that significantly lowers the voltage, which recovers when the fault is cleared. [5]

The three-phase differential productivity mode now includes support for this relay. [15]

The 87UAT relays must also shut down the generator and open the 345 kV breaker. [5] With these grounding systems, the sensitive (59G) relays should be coordinated with the voltage transformer?s primary fuses. [5] In normal operation the 27 relay contacts are opened by the third-harmonic normal voltages, and the super- vising voltage relay 59 contacts are closed. [5] Relay (40) operation is below the dashed directional line and within the larger dashed operating circle. [5] The relay should operate when the dot hits the slope 1 line. [15] High temperature in the unit unbalances the network and the relay operates. [5] The negative sequence relay has a filter circuit which operates only for the negative sequence components. [16] The relay operates when the impedance vector moves into this circle. [5]

The construction of the negative sequence relay is shown in the figure below. [16] An application is shown in Figure 8.18, where the relay has an 88 characteristic. [5]

Other types of protection, such as in Figure 8.3, are not shown. [5] By comparing one winding half against the total, as shown, protection for shorted turns and open-circuited windings is possible. [5]

The intertie protection is usually applied at the PCC location, however, in some cases, it may be located elsewhere within the facility of the owner of the DG. In either case, the intertie protection, along with the proposed settings, require the approval of the associated utility and probably of other oversight entities. [5] Therefore, the protection of this performance can be used as the line of “main protection.” [14] Over-current protection sensitivity coefficient of the calibration is still using (1-7), when the overcurrent protection as the main line protection, the minimum run mode should be used at the end of the line When the short-circuit two-phase current verification, requirements ; when the adjacent line backup protection, the minimum operating mode should be used when the end of the adjacent line two-phase short circuit current to verify, this time requirements. [14]

The protection tripping time is set by the time constant T. [13] Negative- sequence protection may respond, but with long response time, or it may not respond at all. [5] Therefore, with the extension of the scope of protection, will inevitably lead to increased time limit. [14]

This protection scheme is widely used for bus protection and is described further in Chapter 10. [5] This protection will not be actuated for external earth fault. [13] The earth fault can be dispersed by using the restricted earth fault protection scheme. [4] Earth fault loop A basic safety requirement stated in AS/NZS 3000 is the protection of people from “indirect contact? with live parts. [4] Distribution systems and protection against indirect contact and earth fault 5 3 Protection against earth fault 3 Protection against earth fault 3. [4] Medium voltage products Technical guide Protection criteria for medium voltage networks. [4] These protections have a direct action on the tripping coils of the circuit breakers. [13] If we not design our circuit protection properly followed standard guide,it can cause serious injury or death for human and equipment damage. [4]

” Ground Fault “Ground-fault protection of equipment shall be provided Grounding System Theory and Practice. [4] Manohar, N. – Ground fault protection is not required on feeders where there is up-stream ground fault protection. [4]

In our previous post, we have already discussed about electrical protection Systems, devices and units. [13] Nowadays, with electronic and microprocessed protection units, this compensation is done through software. [13] As such, protection requirements for large units differ from those for smaller units. [5]

This will be covered further under the section on ground protection. [5] Where this is possible, high-sensitivity, high-speed protection is obtained, and CT perform- ance does not have to be matched, for there is only one involved per phase. [5] An evaluation of distance protection responses in AC power system with converter-interface. [22] The normal protection may operate in many cases, but not necessarily for all possibilities. [5] This application replaces motoring protection (32) and is more responsive to the conditions just outlined. [5] Protection requirements need to relate to the value of the equipment protected. [5] The protection operating threshold can therefore be reached. [13] This is seldom practical, so other protection must be provided for this area between the flux summation CT and the breaker. [5]

Note that there is a single “Voltage Harmonic” setting and a single “Current Harmonic” setting (plus harmonic phase angle settings for each). [15] Generation” setting lets you reverse the phase ordering, to produce test cases over a wider range of restraint currents. [15] Introduction Theory of core balance CT. A forth earth fault Over Current & Earth Fault Setting Calculations. [4]

The entered values are reflected in the upper grid for the fault phase (B, in this case), and they follow the fault rotation setting. [15] In “Advanced Settings”, make sure “Fault Incidence Angle (FIA)” is set to “Random”, because any other value affects timing. [15]

If the voltage drops below the voltage unit setting, tripping is initiated with operating times about 0.2-0.3 sec. 3. [5] In the “Advanced Settings” menu, a new setting “Time Unit for Auto Test Modes” lets you select “Seconds” or “Cycles”. [15]

On account of these reasons, it is essential that whenever it is possible for an out-of-step swing trajectory to travel through the impedance of the unit transformer or the generator itself, that dedicated relaying to detect such a condition, and initiate an immediate trip of the generator be applied. [5] An alternative connection is to connect the distance relay to CTs and VTs at the generator system bus and set it such that it looks through the unit transformer into the generator. [5] Gen Transformer To system Unit auxiliaries Bus FIGURE 8.4 Unit-connected generator. [5] Unit connected, in which the generator is connected directly to an associated power transformer without a circuit breaker in between, as shown in Figure 8.4. [5]

Magnetizing current, or exciting current, is the current that flows through the primary winding of a power transformer when no loads are connected to the secondary winding ; this current establishes the magnetic field in the core and furnishes energy for the no-load power losses in the core. [13] Whenever there is an unbalancing in between three phases of the power transformer, a resultant unbalance current flow through the close path connected to the common terminals of the CT secondary. [13] An unbalance current will also flow through the neutral of power transformer and hence there will be a secondary current in Neutral CT because of this unbalance neutral current. [13]

It must not exceed the prescribed value, in order to avoid insulation faults, since l oading capability of power transformers is limited mainly by winding temperature. [13] For a solid three-phase fault, I1F1 IaF1 1 0:064 15:70 pu (8:7) I1 pu 100,000 ??? 3 p 18 3,207:5 A at 18 kV (8:8) I1F1 IaF1 15:7 3207:5 50,357:3 A at 18kV (8:9) The maximum load on the unit is Imax load 160,000 ??? 3 p 18 5,132 A at 18 kV (8:10) From this maximum load, a current transformer ratio of either 5500:5 or 6000:5 could be used. [5] A separate differential can be used for the transformer, or without a high-side breaker, include in a bus-transformer differential. [5] If there is no earthing / grounding connection at the transformer location point, this protectio n can also be used to protect against earth faults. [13] Frequently, the voltage transformers are wye-wye, but open-delta- connected VTs can also be used for three-phase voltage. [5] With the generator connected to delta or ungrounded-wye transformers, the third harmonic cannot pass through the transformer wye-grounded winding and circulate in the delta. [5] Power equipment involving iron (rotating generators, transformers, and such) operate close to the knee of their saturation curves. [5] Two primary protective systems are provided both for the generator, as shown, and for the transformer (only one 87TG shown). [5] With larger generators and higher-voltage transmission, the system elec- trical center can move into the unit transformer and also into the generator. [5] The transformer of Figure 8.7 is grounded on the generator side through a 19 V resistor. [5] In some installations and networks MV transformers with rated power up to 630 kVA may be protected against overcurrents by fuses associated to switch-disconnectors, as shown in Figure 2. [13] Transformer overloads can occur during contingency conditions that are the product of one, two, or various system elements being isolated from the power the system. [13] The insulating oil temperature is dependent on the winding temperature, and is used to indicate the operating conditions of the transformer. [13] Out-of- step operation can cause damaging transient forces in the windings of the unit transformer. [5] This is not applicable to those units that are subject to energizing a transformer or power system at full voltage (black start). [5] Loss of voltage transformer signal to relaying or voltage regulator 12. [5]

Generators Transformer 105% continuous 110% continuous 110% 30 min 115% 30 min 115% 5 min 120% 5 min 125% 2 min 130% 3 min 8.12.8 LOSS OF SYNCHRONISM: OUT-OF-STEP For many generators, being out-of-step is a system problem with the electrical center out in the transmission area. [5] Assume that the transformer capacitance between the primary and secondary windings (XCT) is 0.012 mFphase. [5] Cross-compound generators may have the separate units directly connected together to a single transformer, or connected to separate secondary delta windings of a three-winding power transformer. [5] Cross-compound generators have two units, generally connected to a common power transformer. [5]

In this scheme the CT secondary of each phase of electrical power transformer are connected together as shown in Figure 3. [13]

They may be connected to a grounded power system or to the power system through a delta-connected transformer. [5] The output which can be obtained from a transformer without causing undue deterioration of the insulation may be either more or less than the name plate rating depending upon the operating conditions, such as ambient temperature, initial loading, cooling provision, life expectancy, etc. [13] As the load of the transformer does not remain steady and varies according to load curve, the loading of transformer becomes an important operating problem. [13]

Transformer oils are designed to provide electrical insulation under high electrical fields ; any significant reduction in the dielectric strength may indicate that the oil is no longer capable of performing this vital function. [13] For transformers equipped with cooling fans and pumps, the temperature devices are used to automatically start and stop the forced cooling. [13] This is done using matching auxiliary transformers whose role is to balance the amplitudes and phases. [13] Eventually the paper becomes brittle and is not capable of withstanding short circuit forces and even normal vibrations that are part of transformer life. [13] Mechanical impacts during handling and transportation may apply to the transformer an equivalent force above 3g, which can cause distortion and/or displacement of the windings and decrease of the insulation of the windings. [13] The loading of transformer is decided by permissible temperature rise of windings and oil. [13]

They are also equipped to initiate an alarm and a trip for very high transformer temperatures. [13]

Usually, the differential CTs have the same ratio, and they should preferably be of the same type and manufacture to minimize mismatch errors for external faults. [5] There- fore, another scheme operates on the differential voltage between the two ends of the winding. [5]

Most differential relays have a single trace, with each slope occurring only in a specific restraint current range, so that a particular restraint current always selects the same slope. [15] This is many multiples of the differential relay pickup current for positive and fast oper- ation. [5] The 87 differential relays are connected to the generator neutral and circuit breaker CTs. [5] The application recommendations permit the use of sensitive generator differential relays with low percentage characteristics, typically 10-25% for the fixed percentage types and the equivalent or lower for the variable types. [5]

A product- type overcurrent relay, 87GD, operates on the product of the two currents. [5] One type of relay has a minimum pickup of 0.25 product or 0.5 A in each coil. [5] With sensitive voltage relays (59G) applied in high-resistance systems, this voltage can cause oper- ation. [5] The primary winding of the relay has three terminals because of the centre tapping. [16] Underfre- quency relays should allow the load shedding schemes to function first such that the island can be stabilized. [5] A float switch in the relay is used to initiate an alarm signal. [13] Definition : A relay which protects the electrical system from negative sequence component is called a negative sequence relay or unbalance phase relay. [16] Set the ramp rate high enough that it finishes within 800ms, so that the relay will still be in high security mode when the ramp ends. [15] These relays must be insensitive to third harmonics, which normally flow in the neutral in a manner similar to zero sequence. [5]

The total time for Fault 1 and Fault 2 is at most 100ms + 800ms 900ms, which for a 60Hz system is less than the relay’s 60-cycle timeout for high security mode. [15] In Productivity Modes, when you select “51: Inverse Time Overcurrent Relay Test Mode”, the list of basic curve types now includes “Cooper Recloser Time Overcurrent Curve”. [15] There are four types of overcurrent relays; instantaneous, definite time, inverse time and directional overcurrent relays. [4] The construction of induction type negative phase sequence relay is similar as that of an induction type overcurrent relay. [16]

In these cases, supplemental or backup protection is provided by a time- overcurrent relay 51G in the grounded neutral. [5] It can not only protect the entire length of the line, but also can protect the length of the adjacent lines to serve as backup protection effect. [14] Line called near backup protection, for adjacent lines, called far backup protection. [14]

Such protection is included in the excitation system supplied with the ma- chine, but additional protection is recommended to operate independently, as both supplemental and backup protection. [5]

To detect low excitation, partial loss, or complete loss, the diameter is set preferably inside the minimum excitation limiter setting, but out- side the generator capability and stability limit curves. [5] One setting should be about 110% rated voltage to the alarm with a subsequent trip within approximately 1 min, the other set at near 120% rated voltage to trip on the order of 6 sec. [5] Instantaneous overvoltage settings should be about 106-110% of rated voltage to ensure prompt removal. [5]

Set the “Slope to Test” setting to SLP 1, so that result values are calculated based on that slope. [15] In previous versions of the software, from Manual Test you can press F4 (Advanced Settings) then F2 (Set up I/O and Timers) then F9 (Configure Timers) to define programmable timers. [15] The new “Show Sequence Vectors” setting is being set to “On”, to enable the feature. [15]

This setting determines the inter-pulse pause time, typically so a 51 element can fully reset before each test shot. [15] Typical 51 settings should be two to three times the maximum. [5]

It is very important that the settings on under- frequency relaying be coordinated with load shedding schemes. [5] The recommended settings will characteristically coordinate with most load shedding schemes but this should be analyzed on a case-by-case basis. [5]

Note in the image below that two traces are shown on the graph (one for each slope), and there’s a setting for “Slope to Test”. [15]

Sensitivity of 59G is similar to that which can be obtained with 51G. Higher sensitivity and fast operation for ground faults may be obtained by an additional zero-sequence differential. [5] It is preferable not to connect any other equipment in the differential circuit and to keep the lead burden as low as possible. [5]

Generally, the impedance of the restraint winding of differential relays is low. [5] Testing slope 1 is the same as for most differential relays, except that you must apply pre-fault conditions for at least 60 cycles. [15]

A distance relay (40) enclosing this area provides a good means of detecting this condition. [5] For complete loss of field, the distance relay is set as illustrated by the smaller circle in Figure 8.17b. [5] For application of a distance relay, these power curves must be converted to impedances for plotting on the R-X axes. [5]

An auxiliary current transformer can be used to provide internal operating energy with only one zero-sequence source. [5] These types of functions are not routinely applied, but modern utility operating practices try to maximize the utilization of power transformers, which may increase the occurrence of over-temperature conditions and transformer ageing. [13] The rated output of a power transformer is mentioned on its name plate with reference to specified temperature rise under specified test conditions. [13]

For liquid-immersed power transformers, the temperature of the winding hot-spot is the important factor in the long-term life of the transformer. [13] Coordination is also important in some applications to avoid misoperation for ground faults on the high-voltage side of the power transformer. [5]

The new zone settings of the relay R A using the current coefficients ( K 1, K 2 & K 3 ) for different faults with different fault conditions are tabulated in Tables 7, 8 and 9. [21] From Table 7, for the same fault conditions as discussed in Table 4, the reliability of the relay R A has been improved by the proposed PAZSD methodology by changing the zone settings adaptively as per the requirement. [21] From Table 4, for instance, when an LL fault occurred at 50 km from Bus B 1, the relay R A (without the proposed PAZSD methodology) has observed the fault point in Zone-1 which shows that the relay R A operates correctly as per zone settings. [21] From the above case studies, it is understood that the performance of the relay R 12 is satisfactory with new zone settings when a fault occurs on the line 1-2. [21]

Some relays have settings and time current curves just like the low voltage breaker solid state trip devices. [19] AC for over voltage relay variable AC voltage Source0 – 120 / 230 ac for under voltage relay Variable DC voltage source0 – 240v VoltsVariable DC voltage source0 – 400v Volts Fixed AC Voltage source220 V ac – EMI filtered.SWITCHES: CURRENT SELECTOR – 6 RANGES.1A,2A,5A,10A,20A,50A SHORT/ OPEN SWITCH:- For setting theapprox. [11] Fortunately you can suspect of non-operation of relay when the current through the circuit is more than 20% i.e. rated current and hence check & correct the setting. [12] The PAZSD methodology employs current coefficients to adjust the zone settings of the relays during infeed situations. [21] Suppose during commissioning, commissioning engineer made incorrect setting of over current relay to 20% instead of 120%. [12] Even during fault condition when relay is supposed to trip, it won?t as setting is 120% by mistake. [12] It is clear that none of the relays are affected by the infeed condition and the respective relays have properly detected the fault condition with new zone settings. [21]

Built in protection Class CTs for OC relay reverse power relay, Earth fault relay etc.,C5. [11] GRE series relays provide motor protection for Medium Voltage class An alternative method of specifying a CT is to calculate the minimum knee point. [10] Relay protection for multi-terminal lines based on multi-agent technology (pp. 7670-7673). [21] Proper coordination of relays is essential to maintain the appropriate operation of the overall protection system. [17] Motor protection is required to ensure the installations work properly and to protect machines and the Electrical installation guide published by Schneider Electric. the service factors which allow to calculate the heat generated ad size. destruction of the thermal elements in a bimetal relay if coordination is type 1. 22 Apr For more detail setting,please refer manual guide of motor from manufacture. [10]

Nagasawa et al. have proposed an algorithm for protection of parallel MTLs using asynchronous differential currents at each terminal. [21] Forford et al. have designed differential current algorithm for protection of MTLs. [21]

In addition to voltage and current based methodologies, traveling wave-based protection schemes have been proposed for MTL protection. [21] If the rated current of circuit is 2000 A (say), then 2000A of current needs to be flown through the circuit to ensure overall, healthiness of equipment and performance of protection scheme. [12] Protection scheme is generally tested by Secondary Current Inject Test. [12] Protection schemes and fault location methods for multi-terminal lines: A comprehensive review (pp. 1-6). [21] üFor simulation & studying the protection schemes of feeder for under various fault conditions. [11] The above concise discussion underlines the importance of the proposed methodology in improving the reliability of conventional distance protection during infeed condition and impedance faults in MTLs. [21] The results indicate that the proposed PAZSD methodology can improve the performance and the reliability of conventional distance protection during infeed situations under different fault conditions. [21] A concise description of the infeed problem encountered by distance protection in MTLs and proposed solution (PAZSD methodology) under different fault conditions are discussed in the following section. [21] The function of the conventional distance protection may not be accurate for faults with different fault impedances. [21] The protection systems are mainly used to detect and clear faults as fast and selective as possible. [17] üFeeder under fault simulation through Air-cored indicator having minimum of 4 zone of protection. [11] Abe et al. developed asynchronous measurements based protection methodology for fault location in MTLs. [21] The performance and the reliability of the distance protection are influenced by infeed and outfeed currents in MTLs. [21] Network Protection & Automation Guide. ? ? v. the starting current requirements of motors and. [10] üBuilt in fuse protection and built in over current protection. [11] These coefficients are calculated in phasor data concentrator (PDC) at system protection center (SPC) using the current phasors obtained from PMUs. [21]

Amped I Fire protection experts can design fire protection for critical infrastructure such as transformers and indoor equipment. [18]

The main factors which control the total operating time of the relay are TDS and PS, and the fault current is represented by, where where denotes the fault current at the current transformer (CT) initial terminal and is the primary rating of CT. Constants,, and are assigned values 0.14, 0.02, and 1.0, respectively, and that is according to IEEE standards. [17] In coordination studies, the main objective is to minimize the total time taken in operation of primary relays for clearing a fault. [17] The objective function takes the following form: where where is the relay operation time to clear a near-end fault while is its operation time in case of a far end fault. and represent the relays fixed at the ends of the front line. [17] A double line fault (RY) is created at a distance of 200 km from Bus-2 which lies in Zone-3 of the relay R 12 and Zone-1 of the relay R 23. [21] The relay R A malfunctions because the impedance observed by the relay is greater than 21.8388 (distance from the center of the Zone-2 circle to the fault point). [21] The performance of the relay R 12 has been corrected by the proposed PAZSD methodology when a fault occurs on the line 2-3. [21] The impedance trajectory of relays R 12, R 21 and R 23 are shown in Fig. 7, and it is clear that the relay R 12 has detected the fault in Zone-2. [21]

How? When primary current is flowing through the circuit, meanwhile we can check the differential current in the relay. [12] Under normal condition there will be no differential current through the relay. [12]

A relay with time-overcurrent and instantaneous over-current trip functions for phase current, negative sequence current and ground current, is a multi-function relay. [19] The relay won?t trip during primary current injection test as the rated current is flowing through the circuit. [12] Obviously the relay will trip as soon as the current through the circuit is more that 20% i.e. 200A (CT ratio is assumed 2000/1 A). [12]

Study of under voltage relay operation.Study of Over Voltage relay Operation.Study of Over current relay OperationTime characteristic of above relay.DC relaysTime characteristic at different TMSTo study of operating time.To Study of pick up.To Study drop off (reset level).Flag or targetStudy of % error. [11] The main cause for such phenomenon is that the relay R il cannot sense the current ( I q ) flowing from Bus k to l. [21] Therefore, the relay R il under reaches during fault condition. [21] From these case studies (3.3.1.2 & 3.3.2.2) it is observed that because of implementation of the proposed methodology, the relay R 12 could detect the fault condition in Zone-2 (instead of Zone-3), which averts the mal-operation of the relay. [21] This indicates the relays R 12 and R 23 should detect the fault in Zone-2 and Zone-1 respectively. [21] When LG fault occurred at 250 km from Bus B 1, the relay R A has observed the fault in Zone-2, even though the fault is in Zone-1. [21]

From the above three case studies, it is clear that the performance of the relay is affected by the infeed at Bus-2 when a fault occurs on the line 2-3. [21] The constraints of this optimization problem are considered in the second layer of relay, which should respond, if the main layer of relay fails to operate on nearby fault. [17] It is clear that none of the relays are affected by the infeed condition and the respective relays have correctly detected a fault condition. [21] The reliability of the relay had not influenced by the infeed when LG at 50 km, LLG & LLL faults at 150 km from Bus B 1 are separately created as given in Table 4. [21]

A motor relay would require the full load current as a parameter. [19] R. Thangaraj, T. R. Chelliah, and M. Pant, “Overcurrent relay coordination by differential evolution algorithm,” in Proceedings of the International Conference on Power Electronics, Drives and Energy Systems, PEDES 2012, IEEE, Bengaluru, India, December 2012. [17] R. Thangaraj, M. Pant, and K. Deep, “Optimal coordination of over-current relays using modified differential evolution algorithms,” Engineering Applications of Artificial Intelligence, vol. 23, no. 5, pp. 820-829, 2010. [17]

Arbes has developed differential line protection scheme for the protection of double lines, tapped lines and short lines. [21] Differential line protection application to multi-terminal lines (pp. 121-124). [21]

Generator protection against abnormal operating conditions. [11] Protection scheme for the generator with synchronized bus. 2. [11] J. L. Calvo, S. H. Tindemans, and G. Strbac, “Incorporating failures of System protection schemes into power system operation,” Sustainable Energy, Grids and Networks, vol. 8, pp. 98-110, 2016. [17] In-feed conditions jeopardize security in the power system due to the non-adaptive property of distance protection system and provide an obscure view of the system conditions. [21] Despite the simple and dependable performance of the conventional distance protective system, the reliability of distance protection is affected when infeed condition exists in MTLs. [21] The results strongly convey that the proposed PAZSD methodology is effective in improving the performance and reliability of distance protection during infeed condition. [21] The distance protection can protect most of the protected line, and it is virtually independent of the source impedance. [21] Synchrophasor-based backup distance protection of multi-terminal transmission lines. [21] For decades, the distance protection is widely employed for the protection of transmission lines as it is simple and fast. [21] Technological developments in measurements, communication, control and monitoring of power grids have brought a paradigm shift in the protection philosophy of transmission lines. [21] Edinburgh: 1989 4 th International Conference on Developments in Power Protection. [23] B. Zou, M. Yang, J. Guo et al., “Insider threats of physical protection systems in nuclear power plants: prevention and evaluation,” Progress in Nuclear Energy, 2017. [17]

• Insulation Resistance at Test Bed Temperature : Not less than 10 Mega ohm Control Unit: Consisting of MCB DP Input Protection, Indicators for Alarm, Trip & Mains. [11] An example of these relays, which are used as a good technical tool for the protection of power systems, is directional overcurrent relay. [17] H. Leite, J. Barros, and V. Miranda, “The evolutionary algorithm EPSO to coordinate directional overcurrent relays,” in Proceedings of the 10th IET International Conference on Developments in Power System Protection, DPSP 2010, IET, UK, April 2010. [17]

This test does not guarantee the overall connected performance of protection scheme. [12] Primary Injection Test is the last commissioning check to ensure that all the equipment and protection schemes are healthy and working as per the design. [12] • Protection CT’s : Primary side CT’s 10/1A, 5 VA, cl-1, wound primary typeSecondary side CT’s 20/0.67A, 5VA, wound primary type. [11]

üOver voltage – IDMT / DMT characteristics / Under Voltage IDMT / DMT characteristicsüOver voltage / under voltage protection. [11]

The plug settings (PS) depend on the maximum load current and fault current due to short circuit. [17] The current coefficients ( K 1, K 2, and K 3 ) and new zone settings estimated for the above fault condition are tabulated in Table 2 (according to the methodology proposed in section 3.2). [21] The PAZSD methodology which is executed in the PDC sends the new zone settings to the corresponding relay to ensure reliable operation during the infeed condition. [21] The time dial settings (TDS) represent the activation time of each relay and the relay operation is decided by the plug settings (PS). [17] Therefore, the operation of the relay R A with new zone settings is same as with the old zone settings. [21] Z set-new are new three-zone reach settings of the relay R il with infeed line (between Bus k and l ). [21] The zone settings of the relay R A are calculated for 400 km and tabulated in Table 3. [21] Some relays (mostly recloser relays) have a minimum time setting. [19] These new zone settings are updated in the respective relays, and the relay operate as per the new settings. [21] Therefore, the relay does not operate since the observed impedance has fallen out of its zone settings. [21] This proposed methodology guides the relay to change the zone settings according to the infeed conditions using Synchrophasor technology. [21] For relays that have both high and low instantaneous settings, it may be necessary to use two device functions. [19] The range of tap settings which is applicable to the relay. [19] The settings tab for these relays has a slightly different layout as described below. [19] Next suppose, commissioning engineer made incorrect setting of a relay to 120% instead of 20%. [12] The PAZSD methodology employs current coefficients to adjust the zone settings of the distance relays during infeed situations. [21]

The long time pickup current setting below which the device will not trip. [19] The pickup current in the one-line circuit is displayed below Tap Setting. [19] The estimated current coefficients ( K 1, K 2, and K 3 ) and new zone settings and tabulated in Table 2. [21]

• Continuously variable Auto Transformer to vary current 0-20Amp. [11] • Transformer specifications : 3-Phase, 3KVA, 415/240V, delta/star connected transformer with tapings Primary : 0-10-20-100% Secondary – 0-10-20-100% on each phase of windings, Natural air cooled. [11] Provides a list of current transformers connected to the relay in the one-line diagram. [19] Provides a list of ranges of short time or second instantaneous pickup values applicable to the relay. [19] Selectivity constraints on working time of backup relay and the primary relay are given in the following relation: where CTI takes the value 0.3. [17] The objective function of the problem is to minimize the sum of the operating times of all primary relays. [17] Different optimization algorithms are used to solve the relays coordination problems in which the objective function is to minimize activity time of all main relays. [17] Such a relay is divided into two units, that is, the instantaneous unit and the time overcurrent unit. [17] According to, the operating time of relay is defined by and are the lower and upper bounds for relay functioning time, whose values are adopted as 0.05 and 1, respectively. [17] During the optimization procedure, the time taken by primary relays to coordinate with the backup relays is constrained as in where CTI represents the specified coordination time. [17] Some relays (mostly recloser relays) have additional time delays to the regular trip curves. [19]

•3 phase over voltage / under voltage or 1 phase over voltage / Under voltage relay Alstom / Areva / Ashida / ABB / L &T/ Reyrolle•One no of Temperature relay cum indicator – Selectron make. [11] From tables, it is clear that with a change in FR the relay R A with the proposed methodology functions correctly for all the cases regardless of the infeed condition at Bus B 2. [21] For this condition, the impedance observed by the relay R A is 4.011?63.599 0. [23] Figure 14 displays the LabVIEW front panel for relay R A in PDC at SPC (with the proposed methodology). [21] Therefore, the relay operates correctly, i.e. in Zone-1 whereas without the proposed methodology the relay R A operates in Zone-2. [21] The corresponding impedance trajectory of the relays R 12, R 21 and R 23 is shown in Fig. 4. [21] To address the above infeed issue and to ensure reliable operation of the relay R il, the subsequent section proposes the PAZSD methodology. [21] From Fig. 4, it is observed that the relay R 12 has observed the trajectory in Zone-3 whereas the relay R 23 has observed in Zone-1. [21] From Fig. 6, the relays R 12 and R 21 have observed the impedance in Zone-1 and Zone-2 respectively. [21] The effect of the infeed on the relay R A performance has been eliminated by the proposed methodology. [21] The impedance observed by the relay R A is 31.75 ? ? 275.12 0. [21] The reliability of the relay R A has been improved by the proposed methodology for all the case studies as tabulated in Tables 8 to 9. [21] The corresponding impedance observed by the relay R A is 3.9612?65.214 0. [23] The infeed at Bus B 2 has caused the relay R A to mal-operate. [21] The infeed at Bus B 2 has not affected the performance of the relay R A. [21] The infeed at Bus B 2 and FR has influenced the reliability of the relay R A. [21] The relay R 21 has not observed the trajectory in any of its zone due to its inherent directional property. [21] The impedance observed by the relay R A is 48.136 ? 80.37 0. [21] Whereas, the relay R 23 has not observed the impedance in any of its zones. [21] Therefore, it is understood that the infeed at Bus-2 has caused the relay R 12 to mal-operate. [21] Therefore, it is clearly known that the infeed at Bus-2 has influenced the relay R 12 to mal-operate. [21]

The device function type provides the description of the selected relay function. [19] Provides a list of device functions available for the relay. [19] In the case of multifunction relays, different CTs may be used for different device functions. [19]

Number of relay units of the same type that are part of a relay system. [19] There are various types of relays with different operating principles. [17] If the relay is part of a functional group, the group name and type appears here. [19] In such cases, all possible ranges might be included in a relay type in the library. [19]

Provides a list of ranges of instantaneous pickup values applicable to the relay. [19] The second constraint is PS of the relay that takes the following form: and are the lower and upper bounds of PS, whose values are given by 1.25 and 1.50, respectively, while varies from 1 to. [17] According to the number of relays, the value assigned to each of and is 6 and the number of decision variables is 12, and this means to and the variables to. [17]

Negative Sequence relay static 2 No. B5 Field Failure relay 2 No. B6 U V/OV relay micro controller based – 1No. B7 Reverse Power Relay – 1No. Testing Panel: (for Monitoring Measurement and Control) C1. [11] This depends on the variables, TDS, PS, and the minimized working time of relay. [17] This is functionally similar to the time dial and is available in only some relays. [19] To check the efficiency of the proposed algorithm for the three cases, we have minimized the total activity time for each relay. [17] In some recloser relays, the time dial (or time multiplier) also affects the instantaneous time delay. [19] In the one-line diagram, up to 6 CTs can be connected to a relay. [19] Some relays may have different names for this section, such as Short Circuit Instantaneous, Locked Rotor Instantaneous, and so on. [19] Therefore, the relay operates in Zone-2 rather than in Zone-1. [21] Review and analyze daily relay operations for determining correct operation or mis-operation in responding to an electrical system disturbance or anomalies. [20] Start / stop / reset switch- (Elcom) Trip status indicator DUC relay output ‘NO’ or NC’connection facility. [11] Specify the breaker or switching device opened by the relay upon tripping. [19] You can make the desired text appear inside the relay symbol by typing in Function Text (upper) and Function Text (lower). [19] The Relay Device Functions table below displays ANSI/IEEE relay device functions modeled in the EasyPower library. [19]

In order to explain the infeed effect, only relays are assumed to be present in the above power system network (No PMUs, PDC and SPC are present). [21]

To evaluate the performance of distance relay (R A ), numerous faults with different fault impedances (0.2 ?, 1.7 ?, and 4.9 ?) are simulated and discussed in the following section. [21] The performance of the distance relay R A without the proposed methodology is evaluated for various faults with different fault impedances (0.2 ?, 1.7 ? and 4.9 ?) and tabulated in Tables 4, 5 and 6. [21]

The functioning of the distance relays during infeed condition with and without the proposed methodology has been demonstrated through different fault case studies carried out on a four-bus model in PSCAD/EMTDC environment. [21]

Funbashi et al. have proposed methods to identify the fault point in double circuit MTL using measurements from capacitor voltage transformer (CCVT) and current transformer (CT). [21] Transmission lines are occassionally tapped to provide intermediate connections to loads or reinforce the underlying lower voltage network through a transformer. [21] The unit will have two sections of alternators, two sections of sending end transformers with busbars, four sections of transmission lines, four sections of receiving end transformers with busbars and four load sections. [11]

One Number of Three phase, 3KVA, 415/415, Open type star-star transformer provided. [11] üInput / Output transformer 3 phase, 415V/6633-11 volts. [11]

While performing a 3-phase fault calculation, the device function type Ground OC is ignored and Phase OC and Maint Phase OC are included. [19]

If the differential current is equal to sum of individual CT secondary current, this simply means CTs are connected with wrong polarity. [12] If the differential current is zero then CT polarities are correct. [12]

The commissioning of complex protection and control schemes on diverse LV and HV electrical network construction and modification projects. [20] The reliability attribute of the conventional distance protection with and without the proposed PAZSD methodology has been analyzed in this section as per the definition of reliability. [21] The simulation and hardware results prove the efficacy of the proposed methodology in enhancing the performance and reliability of conventional distance protection system in real-time EHV MTLs. [21]

Built in fuse protection and built in overcurrent protection. [11]

RANKED SELECTED SOURCES(23 source documents arranged by frequency of occurrence in the above report)

1. (191) 18) generator protection intertie protection for distributed generati?

2. (110) Earth fault protection theory

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