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  1. 1. 1. INTRODUCTION An electrical power system consists of generators, transformers, transmission and distribution lines, etc. Short circuits and other abnormal conditions often occur on a power system. The heavy currents associated with short circuits is likely to cause damage to equipment if suitable protective relays and circuit breakers are not provided for the protection of each section of the power system, if fault occurs in an element of power system, an automatic protective device is needed to isolate the faulty element as quickly as possible to keep the healthy section of the system in normal condition. The fault must be cleared in a fraction of second. If a short circuit persists on a system for a longer period it, it may cause damage to some important sections of the system. A heavy short circuit may cause a fire. It may spread in a system and may damage a part of it. The system voltage may reduce to a low level and individual generators in different power stations may lose synchronism. Thus, an unlearned heavy short circuit may cause the total failure of the system. A protective scheme includes circuit breakers and protective relays to isolate the faulty section of the system from healthy sections. A circuit breaker can disconnect the faulty element of the system when it is called upon to do so by the issue a command to the circuit breaker to disconnect the faulty element. It is a device, which senses abnormal conditions on a power system by constantly monitoring electrical quantities of the system, which differ under normal and abnormal conditions. The basic electrical quantities which are likely to change during 1
  2. 2. abnormal conditions are current, voltage, phase angle and frequency. Protective relays utilize one or more of these quantities to detect abnormal conditions on a power system. A protective relay does not anticipate or prevent the occurrence of fault; rather it takes action only after fault has occurred. The cost of the protective equipment generally works out to be about 5% of total cost of the system. 1.1 NATURE AND CAUSES OF FAULTS: Faults are caused either by insulation failure or by conducting path failures. The failure of insulation results in short circuits, which are very harmful as they may damage some equipments of the power system. Most of the faults on the transmission and distribution lines are caused by over voltages due to lightening or switching surges causes flash over on the surface of insulators resulting in short circuits. Some times insulators get punctured or break. Sometimes, certain foreign particles, such as fine cement dust or root industrial areas or salt in costal areas or any dirt in general accumulates on the surface of string and pin insulators. This reduces their insulation strength and causes flashovers. Short circuits are lines. Birds may also cause faults on overhead lines if their bodies touch one of the phases and the earth wire. If the conductors are broken, there is a failure of conducting path and the conductor becomes open circuited. If the broken conductor falls to the ground it leads in a short circuit. Joint failures on cables or overhead lines are also a cause of failure of the conducting path. The opening of one or two of the three phases makes the system unbalanced. Unbalanced currents flowing in 2
  3. 3. rotating machines set up harmonics, there by heating the machines in short period of time. Therefore unbalancing of the lines is not allowed in the normal operation of the power systems. Other causes of faults on over head lines are direct lightening strokes, aircrafts, snakes, ice and snow loading, storms and earthquakes, creepers etc. 1.2. Types of Faults Two broad classifications of faults are (1) Symmetrical faults (2) Un symmetrical faults 1.2.1. Symmetrical Faults: A three phase fault is called a symmetrical type of fault. The fault which gives rise to symmetrical fault currents ( that is equal currents with 120 displacement ) is called a symmetrical fault. In a three phase fault, all the three phases are short circuited. There may be two situations, all the three phases may be short circuited to the ground or they may be short circuited with out involving the ground. A three phase circuit is generally treated as a standard fault to determine the system fault level. The following assumptions are made in this type of fault calculation.  The e.m.f.s of all generators are 110 per unit. This means that the system voltage is at nominal value and the system is operating on no load at 3
  4. 4. the time of fault. When desirable the load current can be taken in to account by the super position.  Shunt elements in the transformer model that account for magnetizing current and core loss are neglected.  Shunt capacitor of the transmission line are neglected.  The sub-transient reactance of the generators is generally used in calculations. H 1.2.2 Unsymmetrical faults: Single phase to ground, two phase to ground, phase to phase short circuits, single phase open circuit and two phase open circuit are unsymmetrical types of faults. Single phase to ground (L-G) fault: A short circuit between any one of the phase conductors and Earth is called a single phase to ground fault. It may be due to the failure of the insulation between a phase conductor and earth, or due to phase conductor breaking and falling to the ground. Two phase to ground (2L-G) fault: A short circuit between any two phases and earth is called two phase to ground fault. Phase to Phase (L-L) Fault: 4
  5. 5. A short circuit between any two phases is called a phase to phase fault. Open circuited Phases: This type of fault is caused by breaking of conducting path. Such fault occurs when one or more phase conductor’s break or a cable joint on a overhead lines fails. Such situations may also arise when circuit breakers or isolators open but fail to close one or more phases. During the opening of one of the two phases, unbalanced currents flow in the system, there by heating rotating machines. Protective schemes must be provided to deal with such abnormal conditions. Winding faults: All types of faults discussed above also occur on the alternator, motor and transformer winding. In addition to these type of faults there is one or more type of fault, namely the short circuiting of turns which occurs on machine windings 1.3 Effects of faults: 1. The most dangerous type of fault is a short circuit as it may have the following effects on a power system, if it remains uncleared. Heavy short circuit current may cause damage to equipment or any other element of the system due to over heating or mechanical forces set up due to 5
  6. 6. heavy currents. 2. Arcs associated with short circuits may cause fire hazards. Such fires resulting from arcing may destroy the faulty element of the system. There is also possibility of fire spreading to other parts of the system if fault is not isolated quickly. 3. There may be reduction in the supply voltage of the healthy feeders, resulting in the loss of industrial loads. 4. Short circuits may cause the unbalancing of supply voltage and currents, thereby heating rotating machines. 5. There may be loss of system stability. Individual generators in a power station may lose synchronism, resulting in a complete shutdown of the system. Loss of stability of the interconnected systems may also result. 6. The above faults may cause an interruption of supply to consumers, thereby causing a loss of revenue. High grade, high speed, reliable protective devices are essential requirements of a power system to minimize the effects of a faults and other abnormalities. 1.4. Fault Statistics: For the design and application of protective scheme, it is very useful to have an idea of the frequency of occurrence of fault on various elements of a power system. The following table gives an approximate idea of fault statistics. 6
  7. 7. Percentage Distribution of faults in various elements of a power system. Element % Of total faults Overhead lines 50 Underground cable 9 Transformers 10 Generators 7 Switch gears 12 Ct’s, pt’s, relays & control equipment 12 Table1.0  Frequency of occurrence of different types of faults on a overhead lines: Type of fault Fault symbol % of total fault Line to ground L-G 85% Line to Line L-L 8% Double line to ground 2L-G 5% Three phase 3-Ǿ 2% Table1.1 1.5. Zones of protection: The power system contains generators, transformers, bus bars, transmission lines, distribution lines etc,. There is a 7
  8. 8. separate protective scheme for each piece of equipment or element of the power system, such as generator protection, transmission line protection, bus bar protection. A protective zone covers one or at the most two elements of the power system. The protective zones are planned in such a way that the entire power system is collectively covered by them, and thus, no part of the system is left unprotected. The various protective zones of a typical power system are as shown in fig 1.1. Adjacent protective zones must overlap each other, failing which a fault on the boundary of the zone may not lay in any of the zones, and hence no circuit breaker would trip. Thus, the overlapping between the adjacent zones is un-avoidable. If a fault occurs in the overlapping zone in the properly protected scheme, more circuit breakers than the minimum necessary to isolate the fault element of the system would trip. A relatively low extent of overlap reduces the probability of faults in this region and consequently, tripping of too many breakers does not occur frequently. 8
  9. 9. Fig 1.0 ZONES OF PROTECTION 9
  10. 10. 2. LITERATURE SURVEY 2.1 FUNCTIONAL REQUIREMENT OF THE RELAY Reliability: the ability of the relay to perform correctly when needed and to avoid unnecessary operation Speed: Minimum fault time and equipment damage. Selectivity: The relay must be able to discriminate (select) between those conditions for which prompt operation is required and those for which no operation, or time delayed operation is required. Sensitivity: The relaying equipment must be sufficiently sensitive so that it operates reliably when required under the actual conditions that produce last operating tendency. Economics: Maximum protection at minimum cost and it must be less than 1% of the equipment cost Simplicity: Minimum equipment and circuitry 2.2 Types of feeder protections: 1. Over current protection 2. Distance protection 3. Pilot relaying protection 2.2.1 Types of over current feeder protections: 1. Time graded system 2. Current graded system 10
  11. 11. 3. Time-current graded system TIME GRADED SYSTEM: The selectivity is based on the time of operation of the relays. The relays used are simple over current relays. The time of operation of the relay at various locations is so adjusted that the relay farthest from the source will have minimum time of operation and as it is approached towards the source the operating time increase. Taking an example of 6.6KV system: CURRENT GRADING SYSTEM:  This type grading is done on a system where the fault current varies appreciably with the location of the fault.  This means as we go towards the source the fault current increases. With this if the relay are set to pick at a progressively higher current towards the source. The accuracy of the relay under transient conditions is likely to suffer; current grading alone can not be done.  Taking an example of radial feeder 11
  12. 12. TIME CURRENT GRADED SYSTEM: This type of grading is achieved with the help of inverse time over current relay and the most widely used in IDMT relay. t2 = t1 + t where t is the time step between successive relays 2.2.2 TYPE OF DISTANCE PROTECTIONS 1. Impedance relay protection 2. Reactance relay protection 3. Mho relay protection PRINCIPLES OF DISTANCE RELAYS: Distance relays compares the currents and voltages at the relaying point with the current providing the operating torque and the voltage provides the restraining torque. T = K1I2 + K2V2 + K3VI + K Impedance relay: Restraining torque developed by voltage coil, operating torque by current coil therefore voltage restrained over current relay T = K1I2 K2V2 12
  13. 13. When operating torque is greater than the restraining torque relay is operated K1I2 K2V2 V2 /I2 = K1/K2 Z < K1/K2 The above equation shows circle characteristics: Impedance circle Reactance relay: • In this relay the operating torque is obtained by current and the restraining torque is due to a current-voltage directional element. This means a reactance relay is an over current relay with the directional restraint. The directional element is so designed that its maximum torque angle is 900 T = K1I2 - K3VI T = K1I2 - K3VI 13
  14. 14. T = K1I2 - K3VI For the operation of the relay K1I > K3VI VI / I2 < K1/K3 Z < K1/K3 or X= K1/K3 This means that the resistance component of the impedance has no effect on the operation of the relay. It responds only to the reactance component of the impedance. Characteristics of reactance relay: MHO RELAY PROTECTION: 14
  15. 15. • In this relay the operating torque is obtained by the directional element and the restraining torque due to the voltage element T =K3VI K2V2 For the relay operation- K3VI > K2V2 (K3/K2) V2 / VI Z < (K3/K2) This characteristic when drawn on an impedance diagram it is a circle passing through origin. 2.3 FEEDER PROTECTION: 15
  16. 16. 1. The protection scheme is divided in three zones 2. Zone-1: protects 80% of total line 3. Zone-2: protects total line + 30% to 50% of the adjoining line 4 .Zone-3: protects total line + 120% of the adjoining line Three zone scheme: 2.4. MAIN FEATURES IN DISTANCE SCHEME: 1. Starters 2. Measuring units 3. Timers 4. Auxiliary relays 2.4.1. Starters: The starting relay (or starter) initiates the distance scheme in the event of a fault within the required reach, other functions of the starter are, a) Starting of timer relay for second and third zones b) Starting of measuring elements 16
  17. 17. Measuring units for phases and earth faults can be either directional or non-directional. 2.4.2. Measuring units: It can measure the line impedance, when the line impedance falls below the setting value relay operates. Phase fault units: these measuring units are fed with line to line voltages and difference between line currents (Ia – Ib). They measure the positive sequence impedance from the relay location to the fault point. Earth fault units: These measuring units utilize line to neutral voltage (VAN, VBN, VCN). And phase currents (Ia, Ib, Ic). In order to make these units measure the positive sequence impedance correctly, a zero sequence current compensation is to be provided which is obtained by: KN = (Z0 – Z1) / 3Z1. In the current circuit (1+KN)IA will be fed from above measurement 2.4.3. Timers: Timer relays when initiated by the starter provide the time lag required for the zones. 2.4.4. Auxiliary relays: Distance scheme comprises of several auxiliary relays, which perform functions such as flag indications, tripping, signaling, alarm etc,. 17
  18. 18. 2.5. ADDITIONAL FEATURES IN DISTANCE SCHEMES: 1. Power swing blocking relay 2. VT fuse failure relay 3. Switch on to fault relay 4. Fault locator 5. Auto-reclosing scheme 6. Carrier communication scheme 2.5.1. Power swing blocking: Power swing occurs during system disturbance i.e. Major load changes or dip in voltage due to delayed clearance. The rate of change of impedance is slow in power swing condition and fast in fault condition. The PSB relays use this difference to block the tripping during swings. 2.5.2. VT fuse failure relay: The distance relay being voltage restraint over current relays, loss of voltage de to main PT failure or in advertent removal of fuse will cause the relay. They fuse failure relay will sense such condition by the presence of residual voltage without residual current and blocks the relay. 2.5.3. Switch onto fault: 18
  19. 19. When the line is switched on to a close by fault, the voltage at the relaying point will be zero. Backup zone will normally clear faults of this type. The voltage applied to the relay is low and this condition occurring simultaneously with the operation of starter will cause instantaneous trip by SOTF relay. This SOTF feature will be effective only for about 1-2 seconds after the line is charged. 2.5.4. Fault locator: It measures the distance between the relay location and fault location in terms of Z in ohms, length in KM or percentage of line length. The measurement is initiated by trip signal from distance relays. 2.5.5. Auto reclosing scheme: This scheme comes into action after the clearance of fault. It will automatically close the breaker after the fault is cleared. TYPES OF FAULTS: 1. Transient faults: These are cleared by the immediate tripping of circuit breakers and do not recur when the line is reenergized. 2. Semi Permanent faults: 19
  20. 20. These require a time interval to disappear before a line is charged again. 3. Permanent faults: These are to be located and repaired before line is to be charged. About 80-90% of the faults occurring are transient in nature. Hence the automatic reclosure of the breaker will result in the line being successfully re-energized, thereby 1. Decreasing outage time 2. Improving reliability 3. Improving system stability 4. Reduces fault damage and maintenance time DEAD TIME: The time between the auto reclosing scheme being energized and the 1st reclosure of the circuit breaker. This normally set 1sec. RECLAIM TIME: The time between 1st and 2nd reclosure. The reclaim time will in the range of 10-30 sec, depending on the breaker opening and closing mechanisms. Types of auto reclosing schemes: 1. Based on phase: A) Three phase auto reclosing. B) Single phase auto reclosing 20
  21. 21. 2. Case on attempts of re closing: A) Single shot auto reclosing B) Multi shot auto reclosing 3. Depending on speed: A) High speed auto reclosing scheme B) Low speed or delayed auto reclosing scheme 2.5.6. Carrier communication scheme: The instantaneous zone-1 of the protective scheme at each end of the protected line is set to cover 80% of the line and hence faults in the balance 20% of the line is cleared in zone-2 time, which is undesirable. The 100% of the line can be protected instantaneous by interconnection the distance relays are each end of the by a signaling channel. 3.0 Norms of protection adopted for transmission lines in A.P systems: 220 KV lines: two distance schemes Main-I: Switched schemes fed from bus PT Main-II: Non-switched schemes fed from bus CVT A provision is generally made for changeover of voltage supply for the distance schemes from the bus PT to CVT and vice versa. Each distance scheme is fed from independent CT secondary cores. 21
  22. 22. 400 KV Lines: Two distance schemes Main-I: Switched or numerical distance schemes Main-II: Non switched or numerical distance schemes 3.1 Switched scheme: In the switched scheme, only one measuring unit will be used for all types of faults. This single measuring unit is switched to the correct fault loop impedance by switching in the respective voltages and currents by the starter. The reach of measuring element gets extended to zone- 2 and zone-3 after the elapse of corresponding timings through zone extension process. 3.2 Non-switched scheme: In this scheme there will be 6 starters, 3 for phase faults and 3 for ground faults. There will be independent measuring units for both phase and earth faults for each phase, for all three zones, totaling to 18 units. This scheme is faster and more accurate but costly 3.3. TYPES OF DISTANCE PROTECTION SCHEMES Q MHO: Types in Q-Mho Zone-1 and 2 shaped partially cross polarized directional line. Zone-3 offset lines (adjustable to offset circular mho) 22
  23. 23. Zone-1 and 2 ground faults: quadrilateral with partially crass polarized directional line. Zone-1 and 2 phase faults: shaped partially cross polarized mho with partially directional mho with partially cross polarized directional line Zone-3 ground faults: offset quadrilateral Zone-3 phase faults: off set circular mho 23
  24. 24. 24
  25. 25. 3.4. PYTS: It has three under impedance starters and a single mho measuring unit. One under impedance unit for power swing blocking SETTING RANGE: 0.05to 40 0hms, with starters having range of 20 to 70 ohms. It has an uncompensated U/I starter, which has become a problem due to load encroachment for long lines 25
  27. 27. Static relays can be effectively used for the line protection because these relays are reliable, cheap when compared to electromagnetic relays. Following are the advantages of Static relays: 1. Low burden on current and voltage transformers. And less burden on the D.C auxiliary supply. 2. Absence of mechanical inertia and bouncing contacts, high resistance to shock and vibration. 3. Very fast operation and long life. 4. Low maintenance owing to the absence of moving parts and bearing friction. 5. Quick reset action and to overshoot. 6. Ease of providing amplification enables greater sensitivity. 7. Unconventional characteristics are possible-the basic building blocks of semiconductor circuitry permits greater degree of sophistication in shaping of operating characteristics, enabling the practical utilization of relays with operating characteristics more closely approaching the ideal requirement. 8. The low energy levels required in the measuring circuits permits miniaturization of relay modules. 4.1 STATIC DISTANACE PROTECTION SCHEME TYPE (QUADRA MHO RELAY) 4.1.1 SHPM Relay: 27
  28. 28. It already indicated that the 220KV lines are to be protected by two sets of relays. One as Main-1 having non- switched scheme and another switched scheme, In this chapter a non–switched SHPM relay by M/S GEC Alsthom, Chennai, and supplied to various Electric Utilities and whose function is found to be very much satisfactory for the past 15 years is discussed. This relay is connected to 220kV RTPP Anantapur feeder at Rayalaseema Thermal Power Project. The adopted setting and test results obtained from RTPP are studied and incorporated in this work. The QUADRAMHO relay is a microprocessor based static distance protection specially designed for comprehensive high speed distance protection for HV and EHV transmission lines. Three zones of protection are included, each employing separate measuring elements, one each for three phase-to-phase and three phase to earth faults per zone. Thus a total of 18 elements are provided, there by increasing the reliability of protection. The relay is suitable for both three poles and single and three pole tripping of the circuit breaker. Either bus bar or line voltage transformers may be used as these can be either capacitor VT’s. CT requirements are moderate as the relay is highly tolerant to saturated current transformers. Important features of the relay: 1)3 zone distance relay with 18 non measuring units 2) Different characteristics to suit all lengths and fault levels. 3) Fast operating times over a wide range of fault conditions. 28
  29. 29. 4) Digital synchronous polarizing for close up three phase faults. 5) Micro processed scheme logic with a range of built in schemes selected option switches. 6) Continuous monitoring and on demand periodic self testing. 7) Built in power swing blocking 8) Built in voltage transformer supervision 9) Full range of test features for commissioning and routine testing interfacing enables automatic field test equipment to be used when required. Two models of the relay are available. 1) Zone-1 and 2 shaped partially cross-polarized mho with partially cross-polarized directional line.Zone-3 offset lens (adjustable to off set circular mho) 2) Zone-1 and 2 ground faults: shaped partially cross-polarized mho partially crossed polarized directional line. Zone-3 ground faults:-Off set quadrilateral Zone-3 phase faults: - Off ser circular Mho. The block of the relay and the external connection to the modules are shown in the operation even under noisy condition harmonically distorted wave forms commonly encountered in power distribution systems. The characteristic shapes of the relay ate shown in the enclosed figures. For long lines the lens shaped zone-3 characteristic can be set to avoid the problems of load 29
  30. 30. impedance encroaching into the characteristic. For short line applications involving strong feed of power in feed, the version with quadrilateral ground fault characteristic for all three zones can be specified, ensuring adequate tolerance to arcing and tower footing resistance .The reactance line of the quadrilateral characteristic automatically tilts to compensate for any pre fault power flow to avoid over reach or under reach problems associated with the resistance characteristics having fixed inclination. Synchronous polarization is provided on zone-1&2 to allow correct response to forward and reverse three phase close up faults. LEVEL DETECTORS: To avoid mal operation when a transmission line is de- energized, phase current level detectors are provided. They have a fast operating and reset timings and are connected so as to lock comparator operation. In addition, pole dead signals are generated by current and voltage level detectors which cause the comparators to reset. SINGLE POLE TRIPPING: Following a single pole to ground fault and a single pole trip, the out pit of the ground fault comparator is blocked by resetting of the relevant phase current level detector and comparator is forced to reset by the relevant pole dead signal thus the comparator resets correctly even though the presents of residual current due to load and sound phases cross- polarizing may appear as impedance with in the mho characteristic. 30
  31. 31. PHASE SELECTION: Two variable based neutral current level detectors are provided. The “High set” when operated, blocking the phase- phase comparators thus preventing a 3-pole trip under heavy ground faults. The biasing of the high set prevents is operation for most 2-phase to ground faults allowing the phase-phase elements to give the fastest possible 3-pole trip. The ’low set ‘when not operated blocks the ground faults elements. The biasing ensures that the ground faults elements are blocked for 2 phase ground faults with high fault resistance. The ground faults elements are also blocked for phase-phase or 3-phase faults even with considerable neutral spill current caused, for example by current transformer mismatch. 4.2 SCHEME LOGIC: QUADRA MHO is equipped with integral micro processor based scheme logic which provides 5 schemes as standard selected by a pair of push button option switches X and Y on the front panel of the relay. The standard schemes are: 1) Basic 3-zone distance scheme incorporating a) Variable time delayed zone-2 and 3 tripping. b) Switch on to fault logic to provide instantaneous tripping of close up solid 3 phase faults occurring on line energization c) Voltage transformer supervision logic. d) Power swing blocking logic 31
  32. 32. e) Block to auto recluse logic f) Voltage memory for synchronous polarizing. g) Control of out put contacts. h) Logic to control various internal relay functions. This scheme is included in all others schemes 2) Permissive under reach scheme. Signal aided trip is sealed in until the zone -2 is resets to allow the time for possible breaker failure protection operation in event of a breaker failure for a fault near the remote end of the line. 3) Permissive over reach scheme incorporating current reversal guard feature with variable pick up and drop of time settings. Also includes ‘echo’ feature for rapid clearance of faults near the remote end of the line when the remote breaker is open. 4) Blocking scheme-using reverse looking zone-3 elements with variable aided trip delay timer and current reversal guard feature with variable time setting. A guard feature for low-in feed through faults is also incorporated. An optically coupled isolator is used as a ‘channel in service’ input which, if not energized caused the blocking scheme to revert the basics scheme. 5) Zone-1 extension scheme: This does not require signaling channel. The extension of zone-1 controlled by an input from the auto recluse equipment via,. An optically coupled isolator, each scheme also provides a choice of 3 –pole tripping or single and 3-pole tripping. Visual indicators of faulted phases and 32
  33. 33. zones etc., are given by 9 latched light emitting diodes, which are rest by a push button on the front of the module or at the next trip. Figure 3.1: Zone 1, 2 and 3 Quadrilateral earth faults 4.3 PYTS Relay: The PYTS is a fast and accurate switched distance relay scheme. This employs the mho principle of measurement. It provides phase and earth fault protection and can be applied 33
  34. 34. economically to a short or medium length over head transmission and distribution lines. The scheme is a practical alternative to directional over current protection in power systems but with a multiplicity of in feeds which make grading difficult. Its realistic choice for protection where pilot wires cannot be used and as backup protection on EHV system Complete 3-phase 3 zone distance protection is provided, using a mho characteristic. Residual current compensation is included to ensure that the relay measure correctly under earth fault condition. Features: 1. Minimum Operating lime 2Omsc for zone I protection. 2. Mho characteristic with full cross polarization ensures maximum tolerance of arc resistance on the type PYTS 3. Accurate measurement for source/line impedance ratios up to 100/i. 4. Static circuitry through out imposes low VA burden on current transformer and voltage transformer. 5. Provision for single or 3-phase fault. 6. A switch on to fault facility which provides an instantaneous trip if the line is energized on the 3-phase fault. 7. A relay characteristic angle setting of 30-85 degrees. 34
  35. 35. 8. LED indications with rest. 9. Modular plug in construction with built in test points permits easy maintenance. 10. Compact construction saves panel saves. 11. This scheme provides faster fault clearance time at both ends of the protected line for any faults, occurring on the line. 12. With the signaling channel in service and zone faults beyond the normal zone reach of the measuring element are cleared quickly by means of a trip signal received from the remote and zone measuring unit. 13. Signifying that the fault is internal to the protected line. 14. The trip signal can be arranged by means of selection link either to initiate tripping, provided that the local starters have operated or extended the reach of the measuring element from zone I to a pre determined amount beyond the end of the line by means of instantaneous control enable unit I.C.E Operation: These relays use block comparators to produce the well established and proved mho measuring characteristics. It uses fully cross polarized directional mho measuring element which switched to the correct phase by staring elements phase selection is performed by static phase starter elements S1, S2 and S3, The neutral over current element S4 is fixed to provide 35
  36. 36. remote indication of earth faults and to control zone extinction facility for earth faults only when required. It is also used to over ride the power swing - blocking unit under earth fault conditions when used in conjunction with impedance starter elements. A voltage V is derived from the defaulted phase or phases and a voltage VPOL is taken from a combination of faulted and healthy phases depending on the polarizing characteristic chosen. A signal is proportional to the fault current is provide by transactors T5, T6, T7 and T8 which eliminate the effects of dc transactor, T8 provides zero sequence current compensation the measuring unit characteristic is produced by phase comparator circuit which receives the signal V-IZ and VPOL. A switching network selects b a switching networks according the fault detected by the appropriate starting element an output from the phase comparator is fed into an integrator and then to a level detector to initiate a trip circuit 36
  37. 37. 5.0. Calculation of mho unit settings The positive sequence impedance and zero sequence impedance for the protected line is usually given in the form R+JX from which the magnitude and angle of the impedance can be calculated. Z= Ω/KM Ф=tan-1 (X/R) The equivalent secondary line impedance is obtained by the following formulae. Secondary impedance primary impedance (CT ratio/VT ratio) Secondary line impedance is used for all relay reach settings and calculations. Relay Ohmic setting required reach in KM Secondary Ohms/KM 5.1. Percentage potential Calculation 37
  38. 38. Z1 (primary) = 39.87Ω Z2 ( secondary) = Z1 (primary) *( CT ratio / VT ratio ) = 39.87 * (800 /1 ) * ( 110 / 220000 ) = 15.948Ω 5.2. Settings:- Zone 1 = 80% of secondary line impedance 0.8 * 15.948 = 12.758Ω Time setting required is 0.1 sec. and it need not be set as it is inherent. Zone 2 = Total length of the protected line + 20% of the line impedance of largest line from station 2 . = 1.3 times Z2 = 1.3 * 15.948 = 20.73Ω Time setting required = 300 msec Zone 3 = 1.7 times of Z2 = 1.7 * 15.948 = 27. 1116Ω Time setting required = 600 msec. 5.2.1. ZONE- 1 OHMIC SETTING: 1) Calculate the required zone1 Ohmic reach (normally 80-85% of the line section to be protected). 2) Set to the required fault angle (ФL). 38
  39. 39. 3) Select the range doubling switch KD, and plug tapping KZ for phases A, B and C, such that KD KZ is nearest to, but greater than the required ohmic reach. NOTE: switch KD should always be set at 1 whenever possible and should only set at 2 when required reach exceeds the maximum. KZ tapping or at 0.1 where extremely low zone1 impedance setting are required 4) Divide the required zone1 Ohmic reach by KD KZ. 5) Set the potentiometer K1, in phases A, B and C to the result obtained in (4) above. 6) Check the KD KZ K1 equals the required zone1 reach in secondary ohms (Z1). .ZONE-1 EXTENSION OHMIC SETTING: 1. Calculate the required zone1 extension reach in secondary ohms (normally 120% of the first line section to be protected). 2. Set the zone1 extension potentiometer KC according to the following formulae: KC 5.2..2. ZONE-2 OHMIC SETTING: 39
  40. 40. 1. Calculate the required zone2 reach in secondary ohms, (normally first line section plus 50% of the second line section to be protected). 2. Set the zone2 potentiometer K2, according to the following formulae. K2 5.2.3. ZONE - 3 OHMIC SETTING: 1. Calculate the required zone3 reach in secondary ohms. 2. Set the zone3 potentiometer K3, according to the following formula. K3 NEUTRAL IMPEDANCE OHMIC SETTING: 1. Calculate the required Ohmic setting form the following Formula Required Ohmic setting KD KZ K1 40
  41. 41. Where Z0 Zero sequence impedance of protected line Z1 Positive sequence impedance of the protected line. 2. Choose a KZN tapping such that KD KZN is nearest to but greater than the required ohmic setting. 3. Set the KIN potentiometer, according to the following formula KIN 5.3. SPECIMAN CALCULATION FOR THE RELAY SETTING FOR “PYTS” DISTANCE PROTECTION SCHEME: 1 Length of the protected line 97.88KM 41
  42. 42. 2 Length of the shortest adjacent line section ------------ 3 Length of the adjacent long lie ------------ 4 Conductor size(A) line conductor (B)earth conductor 61/3.18mmACSR 7/9mm 5 Z0/Z1 3.366 6 CT ratio 800/1 7 PT ratio 220KV/110KV 8 CT ratio/PT ratio 0.4 9 Line constant/ Phase /circuit ------------------ A Positive sequence Resistance R1 7.45 B Positive sequence Reactance X1 39.11 C Positive sequence Impedance Z1 39.87 D Zero Sequence Resistance R0 25.93 E Zero Sequence Reactance X0 131.51 F Zero Sequence Impedance Z0 134.04 10 Line angle 79.22 11 Line charging MVAR 13.58 12 Secondary circuit data ---------------- A Line Impedance ZL 15.948 B Distance steps zone-1 reach Z1 12.758 C Line Impedance Z2 20.73 D Line Impedance Z3 27.1116 E Starter reach phase fault Earth fault 63.0 35.22 5.4. RELAY SETTING CALCULATIONS FOR 220 KV RTPP ANANTAPUR FEEDER AT RTPP END WITH “PYTS” SCHEME 42
  43. 43. 1) IMPEDENCE STARTING UNIT These units have variable impedance setting at rated voltage given by the formula Z=K/IN(ohms) The range of k is 20-70 ohms Z=K for 1A relay Starter reach is selected as,. ZA, ZB and ZC Neutral starter current =0.2A fixed 2) POWER SWING BLOCK ING UNIT The setting of the power swing relay should be approximately 30% more than the Starter set impedance Starter set impedance=63Ω there fore PCB impedance is 63X1.3=81.9ohms But the value adopted is 70Ω Time setting adopted is 40mS Position of PSB selector switch P is B position i.e., Power swing blocking of all zones. MEASURING UNIT 43
  44. 44. As the line angle is 79.22degrees the max torque angle of the relay is selected as 800 Zone -1 Ohmic reach=line Ohmic valueX0.8=12.784, say12.8 Therefore KD KZ K1 =12.8 Select Kz =20 and KD=1 so K1=0.64 Zone-2 setting = Impedance value on secondary side is 20.73 Zone-2 potentiometer setting=20.73/12.8=1.619=K2 Zone -3 =impedance value on secondary=27.1116 Zone-3 potentiometer setting =27.1116/12.8=2.11=K3 Zone -1extension Kc =1 Zone 1 extension is nil NEURAL IMPEDENCE SETTING KZN required Ohmic setting (1/3)(Z0/Z1)-1) KD KZ K1 1/3{(134.04/39.82)-1} 12.8 10.09 So select KZN 10 KIN required Ohmic setting/KD KzN 10/1 10) 1 Time settings Time setting Zone-1 inst Zone-2 t22 0.3s 44
  45. 45. Zone-3 t23 0.6 s Starter set up zone-4 1.4s 5.5. SPECIMEN CALCULATION FOR THE RELAY SETTING FOR “SHPM” DISTANCE PROTECTION SCHEME 1 Length of the protected line 97.88KM 2 Length of the shortest adjacent line section ----- 3 Length of the adjacent long line ----- 4 Conductor size (A) line conductor (B) earth conductor 61/3.18mm ACSR 7/9mm 5 Z0/Z1 3.366 6 CT ratio 800/1 7 PT ratio 220Kv/110v 8 CT ratio/PT ratio 0.4 9 Line constants/phase/circuit A Positive sequence R1 7.45 B Positive sequence X1 39.11 C Positive sequence Z1 39.82 D zero sequence R0 25.93 E zero sequence X0 131.51 F zero sequence Z0 134.04 10 Susceptance Yc/2 11 Line angle 79.22 12 Line charging MVAR 13.58 45
  46. 46. 13 Secondary circuit data 14 Line impedance Zl 15.93 A Distance steps zone-1 reach Z1 12.77 B Line impedance Z2 20.64 C Line impedance Z3 27.36 D Starter reach phase faults Earth faults 00 00 E Relay characteristic angle phase & neutral 800 15 Zone-3 reverse reach 1.25 ohms 16 Z0/Z1 3.366 17 Aspect ratio 0.41 5.5.1. SETTINGS ON THE RELAY A) Zone-1 ohmic reach=80% of the length of the line . 15.93×0.8=12.8Ohms B) Select K1+K2=4.8 K1=4, K2=0.8 K1 values on the relay 0 to 4 in steps 1 K2 values on the relay 0 to 0.8 in steps 0.2 Z phase 4.8/1=4.8 C) Divide the zone-1 reach by Zph to obtain the zone-1 multiplying factor (K11+K12+K13)K14=12.8/4.8=2.66 46
  47. 47. Select K11=2.0 K12 =0.6 K13=0.06 K14 =1 K11 values are 1 to 9 and infinity,K12 values are 0 to 0.9 step 0.1 K13 value is 0 to 0.008 insteps of 0.002 K14 value is 1 or 5. D) Zone-2 Ohmic reach as selected from the table is 20.73 ohms (50% of the next line section) divide the required Z2 multiplying factor (K21+K22 + K23)K 24 i.e., 20.73/4.8=4.318 say 4.32 K21=4.0 K22 =0.3 Values of K21 on the relay 1 to 9 insteps 1 K23 =0.02 Values of K22 on the relay 0 to 0.9 insteps 0.1 K24 =1 Values of K23 on the relay 0 to 0.08 insteps 0.02 Values of K24 on the relay 1 to 5 E) Zone-3 ohmic reach (forward) =27.1116 ohms Divide the required Z3 reach by Zph to obtain the Z3 multiplying factor (K31+K32 + K33)K34 = 27.1116/4.8=5.64 K31= 5 K32=0.7 K33=0.04 K34 = 1.0 Values of K31 on the relay 1 to 9 insteps 1 Values of K 32on the relay 0 to0.9 insteps 0.1 Values of K33 on the relay 0 or 0.08 insteps 0.02 Values of K34 on the relay 1 to 5 F) Zone-3 ohmic reach (reverse) =1.25 ohms 47
  48. 48. Divide the required Z3 reach by Zph to obtain the Z3 multiplying factor (K35+K36)K33×K37 = 1.25/4.8 =0.26 (K35=1.0 K36=0.0 K37=0.25 Values of K35 on the relay 1 to 9 insteps 1 Values of K36 on the relay 0 to 0.9 insteps 0.1 Values of K37 on the relay 0.25, 0.5 or 1.0 G) Neutral impedance setting: Zn K4+K5+K 6 =1/3{Z0/Z1 -1} × (K1+K2) =3.78 K4=3 K5=0.7 K6=0.08 Values of K4 on the relay 0 to 5 insteps 1 Values of K5 on relay 0 to 0.9 insteps 0.1 Values of K6 on relay 0 to 0.08 insteps 0.02 H) Zone-1 extension ohmic reach divide the required the Z1x reach by Z1 to obtain the Z1x multiplying factor K15=one As K15=1 no zone extension I) Time setting zone-1 inst Zone-2 0.3s Zone-3 0.6 48
  49. 49. K) Power swing blocking relay (Zone-6 forward):1.3×Zone forward=1.3×27.36=35.6 set automatically with zone-3 setting l) Power swing blocking relay (Zone-6’reverse)=zone-3 reverse+ 0.3 zone-3 forward.1.2+0.3×27.36=9.4 ohms set automatically with zone-3 setting. 6.0. EXPERIMENTATION AND RESULTS PROCEDURE FOR DYNAMIC TESTING OF IMPEDANCE RELAYS WITH ZFB KIT AND CALCULATION OF PERCENTAGE POTENTIAL FOR THE LINE SELECTED: 49
  50. 50. In testing of high speed distance relays it is important to apply simulated fault condition suddenly, other wise the behavior of the relay in service may be different from its behavior in test. Checking the characteristic by reducing the voltage or increasing the current until the relay operation is not realistic, as the voltage and current change instantaneously in magnitude and phase angle when a fault occurs in service. This causes transient mechanical electrical and magnetic conditions in the relay which may cause to over reach unless its operation times exceed 4 cycles during which time the transient conditions would disappear. 6.1. The test kit comprises of • supply unit • control unit • fault impedance unit • External current transformer 6.1.1. Supply Unit: The supply unit will supply potential supply and polarizing voltage to the Relay .On the supply unit a fault selector switch is provided to select the desired fault. This unit comprises the following major components, three single phase transformers ( T 1, T 2, T3 ) ratio 420, 400, 380 / 110, 63.5 volts connected delta / star to form a 3-phase transformer bank. 50
  51. 51. Transformer is used to supply the control unit at 100 volts or 63.5 volts as desired and is continuously rated at 12 Amp secondary output. This transformer also has a further 115 V secondary winding rated at 300 ma to give an auxiliary supply to the fault contactor in the control unit transformer 2 and 3 are used to supply quadrature of polarizing voltage to relay that require such voltage in addition to the normal fault voltage. These transformers are continuously rated at 1 Amp secondary output fault selector switch is included to facilitate quick selection of fault in the scheme. When injecting into a neutral connected measuring relay the fault voltage and current are supplied from transformer T1 of main supply bank while the transformers T2 & T3 supply the necessary quadrature voltage for the starting of relay in the scheme. When injecting into a phase to phase connected measuring relay the fault voltage and current are again supplied from transformer T1 6.1.2. Control Unit: This unit comprises the following major components. • This source impedance (L2), tapped to provide a range of 0.5 to 24. This impedance used to control the relay current and vary the source to line ( fault) impedance ratio, in conjunction with the fault impedance L1 and R1 • The voltage auto transformer T4 which is connected across the line impedance via the fault contactor , is tapped in 10% and 1% steps from 0 to 110% this 51
  52. 52. permits a precise setting of voltage to be applied the relay and allows the fault impedance to be matched to the relay impedance setting. The fault contactor is energized from 115 A.C. Supply from the supply unit via bridge rectifier and push button. Normally open contact of the fault contactor is brought out to terminal to start an external timing device when required the current reversing switch S3 is included to enable the current supplied to the relay to be reversed and so check the relays are measuring in the correct direction. The control unit comprises source impedance tapped to provide a range of 0.5 to 24 ohms. A tapped autotransformer in the unit allows matching the kit with the line impedance and applying correct potential to the relay under the faulty conditions. It also provides for pre fault current to the relay under test. It also provides a current reversing switch to supply current in reverse direction while testing the relay for reverse reach. 6.1.3. Fault impedance Unit: This unit represents the line impedance as seen by the relays under the fault conditions. The impedance is made of choke (L1) and a resistance (R1) .The choke has an ohmic reach of 0.5 to 24 ohms in 8 steps .The resistance has 15 steps ranging from 0.2 to 10 ohms. By providing a jumper between the selected tap on the reactance and resistance taps the required line resistance along with the power factor can be obtained .Connecting the kit and selection of impedance and calculation of % potential and error in the relay operation .The ZFB kit is to be connected as shown in the drawing enclosed it .The kit is to be supplied with 400v supply 52
  53. 53. between RY&B phase with correct phase sequence. For correct phase sequence is not maintained the kit will not work properly. The testing of the relays involves choosing of correct fault impedance on the kit for phase-to phase faults and phase to neutral faults and for zones .The values to be tested are indicated in the in the tabular form along with the fault impedance values and impedance values and CT ratio of the interposing transformer in the ZFB kit. After section of the impedance on the kit the % potential for which the relay has to operate is to be calculated and the relay tested. P1-p/100 will give the percentage error. The error should not be more than 5%. The reactance and resistance taps chosen on the fault impedance kit should be such that the resulting impedance should gives the nearest value above that. 6.2. Calculation of percentage potential to test the relay with ZFB kit (SHPM Relay) %Potential for phase faults:- Impedance value on the kit 2x relay setting/CT ratio of the kit 53
  54. 54. % potential for earth faults: - (1+K) relay setting /CT ratio of the kit Z for phase faults Zone-1 2×12.758/(5/2)=10.2 79.22 Zone-2 2×20.73/(5/2)=16.58 79.22 Zone-3 2×27.1116/(5/2)=21.68 79.22 Value selected on the impedance kit R X Z θ 1 8 25 82 % potential for phase faults 1xrelay ohmic value/value on the kit % potential for zone-1 phase faults 2x12.758/25x (5/2) =40.82% % potential for zone-2 phase faults 2x20.73/25x (5/2) =66.33% % potential for zone-3 phase faults 2x27.1116/25x (5) =43.37% % potential for zone-31 phase faults 2x1.2/25x (1) =9.6% Earth fault compensation factor K=1/3{(Z0/Z1)-1} =1/3(3.366- 1) =0.78 % potential for earth faults (1+K) x relay ohmic value/value on the kit % potential for zone-1 earth faults 1.78×12.758/25× (5/2) =36.33% 54
  55. 55. % potential for zone-2 earth faults 1.78×20.73/25× (5/2) =59.03% % potential for zone-3 earth faults 1.78×27.1116/25× (5) =38.6% % potential for zone-31 earth faults 1.78×1.2/25×1 =8.54% RESULTS: Comparing of theoretical values with actual values tested on the kit with the calculated and adopted settings Name of the feeder: 220KV RTPP-ANANTAPUR AT RTPP END Type of the relay SHPM Sl.n o Zone/p hase Relay set VALUE /time Tim e of Ope rati on Value on ZFB kit The oret ical valu e Test valu e R X Z θ CTS 1 Zone-1 A-n 12.758 Ω int 1 8 25 82.5 5/2 36.3 36 2 B-N 36 3 C-N 36 4 A-B 40.8 2 40 5 B-C 40 6 C-A 40 7 Zone-2 N-N 20.73 300 ms 59.0 3 59 8 B-N 59 9 C-N 59 10 A-B 66.3 3 64 11 B-C 65 12 C-A 65 13 Zone-3 27.11Ω 5/1 38.6 38 55
  56. 56. A-N 600ms 14 B-N 38 15 C-N 38 16 A-B 43.3 7 42 17 B-C 43 18 C-A 42 19 Zone-31 A-N Forward 1.2Ω 1 8.54 8 20 B-N 8 21 C-N 8 22 A-B 9.6 9 23 B-C 9 24 C-A 9 6.3. TESTING OF THE RELAY ON THE ZFB IMPORTANCE RELAY KIT (PYTS Relay) Fault impedance required on the kit 2Z1/N Phase to phase faults =1Z1/N Phase to earth faults = (1+K) Z1/N Where Z1 = relay ohmic reach N = CT ratio on the ZFB kit, K = earth fault compensation factor calculated earlier %POTENTIAL CALCULATION: 56
  57. 57. Phase to phase faults =2Z1/NZt Phase to earth faults = (1+K)Z1/NZt Where Zt= importance value selected on the kit .For phase to phase faults CT ratio selected on the kit (5/2) Z on the impedance kit for Zone-1 =2×12.8/ (5/2) =10.24 Zone-2 =2×20.73/ (5/2) =16.58 Zone-3 =2×27.1116/ (5/2) =21.68 Where Zt = impedance value selected on the kit. For phase to earth faults Earth fault compensation factor K=0.78, (1+K) =1.78 Z on the impedance kit for Zone-1 = 1.78×12.8/ (5/2) =9.11 Zone-2= 1.78×20.73/(5/2) =14.75 Zone-3= 1.78×27.1116/ (5/2) =19.3 Tap selected on the ZFB kit for selection of impedance R X Z ANGLE 1 8 25 82.5 PERCENTAGE POTENTIAL CALCULATION: Z O N E CT RATIO PHASE TO PHASE PHASETO NEUTRAL 1 (5/2)=2.5 2×12.8/25×2.5=40.82 1.78×12.8/25×2.5=36.45 2 (5/2)=2.5 2×20.73/25×2.5=66.33 1.78×21.76/25×2.5=59.03 3 (5/1)=2.5 2×27.1116/25×2.5=43.37 1.768×28.16/25×5=38.6 57
  58. 58. 6.4. TEST RESULTS OF PYTS RELAY Name of the feeder: 220kv R.T.P.P.-ANANTAPUR Type of the Relay : PYTS 104 S.n o Zone/ phase Rel ay Set Tim e (m sec Time of operati on (m sec) R X ZLФ CT ratio On ZFB Kit %Reac h Theore tical Value %Rea ch Practi cal value 1 Zone- 1 A-N INS T 72.8 1 8 25L 82.5 5/2 36.45 36 2 B-N 76.7 36 3 C-N 75.5 36 4 A-B 82.9 40.82 39 5 B-C 83.5 40 6 C-A 82.6 40 7 Zone- 2 A-N 300 372.6 5/2 59.03 62 8 B-N 384.1 60 9 C-N 377 61 10 A-B 380 66.33 66 11 B-C 379.3 66 12 C-A 379.8 66 13 Zone- 3 A-N 635.3 5/1 38.6 40 14 B-N 635.3 40 15 C-N 629.9 40 16 A-B 658.1 43.37 43 17 B-C 646.0 43 58
  59. 59. 18 C-A 647.9 43 6.5. DISCUSSION OF RESULTS The line data for 220KV Ananthapur line and the various settings are, Zone-1 - instantaneous tripping. Zone -2 - 0.3sec Zone-3 - 0.6 sec Starter - 1.4sec Power swing blocking unit setup For SHPM relay is 35.6 ohm. For PYTS relay is 70 ohm. Corresponding zone-1, zone-2, zone-3 settings were set on the potentiometer. With all the above setting the static relays which were adapted for Anantapur 220 kV line is functioning properly. 1 Length of the protected line 97.88KM 59
  60. 60. 2 Length of the shortest adjacent line section ----- 3 Length of the adjacent long line ----- 4 Conductor size (A) line conductor (B) earth conductor 61/3.18mm ACSR 7/9mm 5 Z0/Z1 3.366 6 CT ratio 800/1 7 PT ratio 220Kv/110v 8 CT ratio/PT ratio 0.4 9 Line constants/phase/circuit A Positive sequence R1 7.45 B Positive sequence X1 39.11 C Positive sequence Z1 39.82 D Positive sequence R0 25.93 E Positive sequence X0 131.51 F Positive sequence Z0 134.04 10 Susceptance Yc/2 11 Line angle 79.22 12 Line charging MVAR 13.58 13 Secondary circuit data 14 Line impedance Zl 15.948 A Distance steps zone-1 reach Z1 12.758 B Line impedance Z2 20.73 C Line impedance Z3 27.1116 60
  61. 61. D Starter reach phase faults Earth faults 00 00 E Relay characteristic angle phase & neutral 800 15 Zone-3 reverse reach 1.25 ohms 16 Z0/Z1 3.366 17 Aspect ratio 0.41 6.6.Name plate Details of SF6 circuit breaker. Make: Cromprton greaves limited, Nasik, India. Type : 200- SFM – 40A Rated Lighting withstand voltage : 1050KVp Rated short circuit breaking current : 40 KA Rated operating pressure : 15 Kg /cm2 First pole to clear factor : 1.3 Rated duration of short circuit current: 40 KA-3 sec Gas weight: 2 kg SC no: 5145C Year: 1993 Rated normal voltage: 245KV Rated normal current : 2500A Rated frequency: 50 Hz 61
  62. 62. Rated closing voltage: 220V D.C Rated opening voltage: 220V D.C Rated gas pressure: 6Kg /Cm2 (at 200 C) Rated voltage and frequency for auxiliary circuit : 415V, A.C, 50 Hz Total weight with gas: 3900 Kg. 6.7. Name plate Details of voltage Transformer: (PT’s) Make : Transformer and Electrical kerala Limited, Type :CPUEGLV Frequency : 50Hz Oil quantity : 200 L Insulation level : 460 /1050 KV Weight :1200Kg Highest system voltage : 245KV Method of connection: Between line and earth in an effectively earthed neutral system. No. of phases: 1 Type of T/ f - earthed Maker 730064-5 Year 1993. 62
  63. 63. Secondary winding no 1 2 Measuring Protection Output 500mvA 100VA Accuracy class 0.5 /3P 3P Primary Terminals A1 A2 Secondary Terminals 1a1,1a2 2a1,2a2 Voltage factor 1.2 continuous 1.5 /30 sec Voltage ratio 220 /1.732Kv/ 110/ 1.1732V 220/1.732Kv/ 110/1.732V 6.8. Name plate Details of Current Transformer: Manufactured by WS Industries (India Ltd.,) Bangalore – India Frequency: 50 Hz Highest system voltage: 245 KV Basic insulation Level : 460 /1050 Kv Oil Weight: 360 Kg Total weight: 1250Kg Ratio: 800 /1-1-1-1-1 Core NO 1 2 3 4 5 Rated primary 800 800 800 800 800 63
  64. 64. current A Rated secondary current 1 1 1 1 1 Output VA --- ----- 50 --- --- Accuracy class PS PS 0.5 PS PS Turns ratio -- 2/1600 -- 2/1600 --- Resistance of CT at7500 C 3 3 ---- 3 3 KVP(V) 1000 1000 -- 1000 1000 64
  65. 65. 65
  66. 66. BIBLIOGRAPHY 1. SUNIL.S.RAO. Switch gear protection and power systems Khanna publications, eleventh edition 2. CL WADHWA Electrical power system, New age international, third edition. 3. BADRI RAM, DN VISWAKARMA , Power system protection and switch gear , TATA Mc GRAW HILL 4. IJ NAGARTH, DP KOTHARI, Modern power system analysis TATA Mc GRAW HILL. 5. Company manual for PYT,SHPM ralay setting by GEC Alstom India ltd. 6. R.T.P.P. Electrical manual. 66