Power Supply Installation PDF

PROTECTION SCHEME OF TRACTION SUB STATION (Extract of RDSO Specn No. ETL/PSL/65(8/84) 5.0 POWER SUPPLY SYSTEM Power is received from the supply authorities grid network at 132KV or 110KV or 66 KV either at individual...

PROTECTION SCHEME OF TRACTION SUB STATION (Extract of RDSO Specn No. ETL/PSL/65(8/84) 5.0 POWER SUPPLY SYSTEM Power is received from the supply authorities grid network at 132KV or 110KV or 66 KV either at individual traction sub station(TSS) or at a single point of supply from where at as transmitted through railway’s own 132/110/66KV transmission line to the various sub-station location, with line sectioning facilities provided as required 25KV power supply for traction is derived through 132 / 25 kv or 66 / 25 kv single phase transformer the primary winding being connected to any two (nominated) phases of the incoming three phase, two phase line and on the secondary side one terminal of the 25kv is connected to the traction overhead equipment (OHE), the second terminal being solidly earthed and connected to the running track rail each transformer has its associated breaker on the 132/110/66KV and 25KV sides , with a separate set of 25KV breaker called feeder breaker for feeding the traction overhead lines (OHE).Adjacent sub- station are fed from diffrent phase of the three phase system in rotation and neutral section or dead section(SP) are provided on the 25KV OHE and for sectioning and fault location and maintenance of OHE.The OHE supply is switch ON or OFF through intrruptors (load switches) which do not open on fault but can be closed on fault.The fault is cleared by feeder circuit breakers.The 25KVtransformer beaker serves as back up protection Normally power supply from a sub-station extend upto the neutral section on either side, but in case of an emergency, necessitating the total shut down of a sub-station, power supply from adjacent sub-station, on either side as extended upto the shut down sub-station by bridging the neutral section through intrruptor. 5.1 BOOSTER TRANSFORMERS In order to reduce inductive interference in adjacet telecomminication circuit booster transformer on certain section of electrified track installed in series with the 25KV traction overhead equipment.The primary winding of the booster transformer is connected to the 25KV overhead equipmdent.The primary winding and the secondary winding as in series with the return conductor which is strung close to the 25KV overhead equipment.Booster transformer with a rating of 100KVA provide necessary voltage to force the traction return current from the rail and earth to flow through the return conductor.The booster transformer have a leakage impedence of about 0.15 ohm each and are spaced about 2.66Km apart. 98  5.2 PROTECTIVE RELAYS AT THE TRACTION SUB-STATION For protection of transformer, sub-station and the feeder,the following relays are provided on control panel housed in the masonry cubicle at the traction sub-station(TSS) i) FOR THE TRANSFORMER PROTECTION a) Differential relays b) IDMT overcurrent Relays for the primary (HV) as well as for the secondary (L.V) side, The IDMT relay on the (HV) side is also provided with an instatenous overcurrent element c) Instantaneous Earth Lekage relays on the primary(HV) side as well as on the secondary (LV)side. d) High speed Inter tripping Relays e) Auxiliary relays for transformer fault i.e Buchholz Excessive Winding and Oil Temperature trip and alarm and Low oil level alarm ii) FOR THE OVERHEAD EQUIPMENT PROTECTION a) Admittance type directional Distance Protection relays b) Admittance type relay for protection against Wrong phase coupling c) Instantaneous overcurrent Relays. d) Panto flasover Relay e) Delta I relay for high resistance fault. 5.3 AUTO-RECLOSING OF FEEDER CIRCUIT BREAKERS A single shot auto reclosing scheme for 25kV feeder circuit breakers(s)at AC traction sub-station has been adapted to faciliate reclosing of the 25kV feeder breaker automatically once after a pre-set time delay after tripping of the circuit breaker on OHE fault.This feature will help in quick restoration of traction power supply to OHE if the fault is of a transient nature.It will also help in checking/restricting the continuance of arc in the event of the pantograph of a moving locomotive passing the overlap opposite feeding post at such moment and thus protecting the OHE,catenary in paricular,from consequent damages. 5.4 INTER-TRIPPING OF FEEDER CIRCUIT BREAKERS In the event of failure of a traction sub-station,25kV supply is extended from the adjacent sub-station by closing the bridging interruptors at SPs.Under such emergency feed condition, wrong phase coupling may be caused at the overlap opposite the failed sub-station by the pantograph of a passing locomotive,resulting in the tripping of 25kV Feeder Breaker at 99 any one of the two sub-staion through Wrong phase Coupling (Mho) relay. This may result in the formation of an arc at the overlap due to which the OHE may be damaged. The damage due to the arc can be minimised by tripping the feeder circuit breaker at the other sub-station also.This is achieved by an intertripping arrangement through the Remote Control Equipment. 5.4.1 For the purpose of calculation,the values of loop impedance with earth return for the OHE are taken as under at 700 phase angle i) Single track OHE 0.41 ohm/km ii) Double track OHE 0.24 ohm/km iii) Single track OHE with 0.70 ohm/km RC iv) Double track OHE with 0.43 ohm/km RC 5.5 GOVERNING SPECIFICATIONS The main component covered by this specification shall confirm to the following standard specification (latest version) which shall be applied in the manner altered, amended or supple mented by this specification and Indian elecricity Rule where applicable i) Elecrical relays for power IS:3231 - 1965 system protection ii) static protective relays IS:8686 - 1977 iii) Elecrical indicating instrument IS:1248 - 1968 iv) Control cable IS:694 - 1977 v) Interposing current transformer IS:2705(4)1981 5.6 RELAYS 5.6.1 The relays shall be of the draw-out(plug-in)switch board type,back-connected and suitable for semi-flush mounting provided with dust-tight covers of dull black enamel finish. 5.6.2 The relays shall be provided with test plug or seprate test blocks for secondary injection tests.The relays parts shall be easily accessible with the relays mounted on the panels. The terminal connections inside the relay’s housing shall be such that when the relay is drawn-out the current terminal of the CT secondaries get shorted automatically.Since the sub-stations are normally unattended, the relay shall be of self-reset type except for the following which shall be of hand-reset type : i) Low oil level alarm. ii) Winding temperature indicator alarm and trip. 100  iii) Oil tempreature indicator alarm and trip iv) Buchholz alarm and trip v) Auxiliary unit in defferenthial relays 5.6.3 In addition, wherever necessory for proper functionig of scheme hand reset con- tact in auxiliary relays shall also be provided.All the protective relays and all those associated auxiliary relays in the circuit of alarm and annunciations etc including inter trip relays shall have flag type operation indicators with manual reset service suitable for operation from the font of relay cases. 5.6.4 The current coil can be rated for the continuous current of 5A.The voltage coils shall be rated for 110Vdc.The contact of relays shall be silver plated. The current coil shall be capable of withstanding 20% overload for 8hrs. 5.6.5 The relays shall be test voltage class 2 as per clause 3.2 of IS 8686-1977 5.6.6 The auxiliary relay coils shall be designed for continuous service voltage of 110 V dc and shall be capable of satisfactory operation up to atleast-20% fluctuation in voltage 5.6.7 The output of relays shall be capable of operating the armature attracted type auxiliary relay which shall have a burden of above 20VA at 110V dc. 5.6.8 the relays shall have name plates with rating data, serial number and manufacture’s name marked on them.The metal case shall be provided with seprate earthing terminal. 5.6.9 The basic requirement of the scheme of protection are indicated in clause 20 to 23. The tender shall furnish full detail of the protective scheme offered together with the char- acteristics of relays and typical circuit diagram. 5.7 STATIC TYPE RELAYS The Indian Railways have been using Electro Mechanical type relays manufactured by Ms English Electric co. of india ltd.,(GEC-ALSTHOM) for 25KV Traction sub-station. SN Description type Rating/setting design range A) TRANSFORMATION PROTECTION 1. Tra’nsformer percentage DDT-12 Current setting 40- baised diffrential -100%of 5A,20%,30% or 40% 5A Bias setting 2. IDMT overcurrent relay CDG-26 CDG 16,80-320% of 5A combined with CAC-13 CAG-13 400-1600% of 5A instateneous high set overcurrent(132KV sdide) CAG-14 10-40% Of 5A 3. Restricted earth 101  fault relay (132KV&25KV side) 4. IDMT overcurrent relay CDG-16 80-320% Of 5A (25kv side) 5. Aux relays for buchholz VAA-33 excessive winding and oil tem tripping B) OHE PROTECTION 1 MHO type directional YCG-14 0.33 to 12 ohm extended distance protection zone each upto 60 ohm relay(DPR) of 5A with MTA 75 de gree 2 MHO relay for protection YCG-14 0.33 to 12 ohm extended against wrong phase zone reach upto 60 ohm coupling(WC) of 5A with MTA 125 de gree with forward offset of 11% 3. Instantaneous high set CAG-17 100-800%of 5A over current relay on 25KVside(OC) C) AUXILIARY RELAYS 1 D.C Supervision i) Transformer HV CB VAA-11 Trip supervision ii) Transformer LV CB VAA-11 iii) 25KV Feeder control VAA-11 iv) 25KV intrruptor control VAA-11 v) 5.DC fail alarm cancel VAA-11 vi) Alarm annunciation VAA-11 control SN Discription Type Rating/setting design range 2. Auxiliary realy for VAA-11 contact multiplication of directiional distance protection relay(YCG-14) 3. Alarm bell realy VAA-21 4. Flasher relay VAA-21 5. Timer relay for single VAT-11 shot Auto-Reclosing 102  scheme 6. Auxiliary relay for VAA-61 Auto reclosing scheme 7. High speed Master trip VAJH-13 relay 8. High speed inter trip VAJH-13 relay 9. Auxiliary relay for VAA-43 Buchholz oil temp/ winding temp/low oil alarm 10. Alarm annunciation relay VAA-121 5.8 SCHEME OF PROTECTION FOR 132/25 KV OR 110/25 KV OR 66/25 KV TRANS- FORMER 5.8.1 Differential protection Protection against internal fault shall be provided by means of a senstive single-pole diffrential relays. The relays shall be of the high speed type and shall operate in less than two cycles.The relays shall incorporate the following feature i) There shall be no necessity for changing the setting of relays when the transformer tap is changed.The transformer is provided with tap from -15% to +10%. ii) Necessary harmonic restraining feature shall be incorporated to prevent operation due to in rush of magnetisation current when the transformer is charged either from the HV or the LV side. iii) The relays shall not operate for maximum through fault current. iv) The current setting of the relays shall be adjustable, preferably between range of 20% and 80%.The minimum current setting shall be as low as possible to obtain better senstivity. v) Adjustable bias setting should also be provided.The bias at minimum operating current setting shall be 20%,30% or 40% to suit the tapping range of the traction transformer and other designed considerations. The relays shall be connected to bushing type current transformer provided in the bushings of 132/25 kV,110/25kV transformer.However,interposing current transformers of suitable ratio and ratig with matching charcteristics of knee point voltage , excitation current etc. shall be provided with the diffrentialrelays in order to boost up the bushing CTs secondary current, at full load, to a value equal to relays rated current.Magnetisation ratio error curves for the crrent transformers 103 will be supplied to the successful tenderer to enable him to match the characteristics of the relays and iterposing CTs with those of the current transformer. 5.8.2 Earth Leakage Protection Back up protection for internal earth fault within the transformer shall be provided by means of a senstive ,high speed ,earth leakage. Such relays shall be provided separately for both the primary and secondary side the relays shall be connected to separately mounted current transformer.The relays shall be adjustable between 20% and 40% of 5Amps in equal step at 5%. The relays shall be of T-10 class with operating time not exceeding 10 ms. 5.8.3 Over current protection Protection against over current in the transformer shall be provided by means of single- pole non directional overcurrent relays with inverse definite minimum time lag characteristics both on the primary and the secondary side of the transformer.Further an additional instantaneous over current relays shall be provided on the primary side. On the primary side the over current relays shall be connected to separately mounted current transformers. On the secondary side the over current relays shall be provided only on the live (unearthed) leg of the secondary terminal and shall be connected to a seprately mounted current transformer.The overcurrent relay on the secondary side shall serve as back up protection against fault etc.The over current relays on the primary side shall serve as back up to the diffrential and earth leakage relays against heavy fault. Proper discrimination shall be maintained in the operation of these two sets of overcurrent relays. The setting on these relays shall be adjusted between Relay Position current Time multiplier setting setting i) IDMT overcurrent 80% to320% 0 to 3 secs. on primary side ii) Instantaneous over 400% to 1600% current on primary side. iii) IDMT overcurrent 80% to 320% 0 to 3secs. on secondary side. The instantaneous relays shall be of T10 class with operating time not exceeding 10 ms at 5 timesthe current setting. 5.8.4 The diffrential relays and earth lekage relays both on the primary and secondary sides as also the over current relays on primary side shall cause inter-tripping of the 132/110/ 66KV and 25KV circuit breakers associated with the transformer.The inter-tripping of the associated transformer circuit breakers on HV and LV side shall also be effected due to other faults in the transformer ,namely Buchholz trip. The IDMT over current relays on the secondary side shall, however, trip the respective circuit breaker on 25KV side only.The inter-tripping of associated transformer circuit breakers envisaged above shall be effected through a high speed tripping relay with ‘hand reset contact.Such inter tripping relay shall lock out the closing of circuit breaker from all mode of closing commands viz. remote control,local at the panel and also at the circuit breaker mechanism, until the inter-trip relay or the lock out relay (if provided separately),is reset manually. 104 5.8.5 Other protective devices The transformer as supplied by the purchaser will be fitted with following warning and protective devices. i) Low oil level alarm. ii) Buchholz relay with alarm and trip contact. iii) Oil temperature indicator with alarm and trip contact iv) Winding tempreature indicator with alarm and trip contact These contact shall be wired up to a weather proof terminal box mounted on the trans- former by the transformer manufacturer.The connection shall be extended to the alarm and trip circuit as well as to annunciator provided on the control board. 5.9 SCHEME OF PROTECTION FOR 25KV OVERHEAD EQUIPMENT 5.9.1 The sub-station equipment as well as the over head equipment is protected against short circuit and over load by means of feeder circuit breakers.Norally the tracks on one side of the sub-station are fed through one feeder circuit breakers in case defect on one feeder,the other feeder circuit breaker is arranged to feed track on both side of the sub- station.To protection scheme shall full-fill the following function i) To detect all short circuit over the zone of overhead equipment fed by the feeder circuit breaker. ii) To operate with minimum delay in opening the circuit breakers. iii) To refrain from operation at the maximum working current i.e discriminate between the maximum load currents and short circuit current even though the magnitude of the former is at time more than the latter especially when the fault are remote from the sub-station iv) To detect and isolate fault on the OHE caused by accidental coupling of two differ- ent phase from adjacent sub-station v) To provide single shot auto-reclosing of the feeder circuit breaker after a present time interval adjustable between0.5secs.to 30 secs. vi) To reclose the 25kv feeder circuit breaker through single shot automatic reclosing scheme in the event of feeder circuit breakers tripping on fault through any of the three relays viz.admitance(MHo)relay for wrong phase coupling and instantaneous over current relay. vii) To detect and isolate the flashover caused by pantograph on an overlap in front of Traction Substation when panto moves from live to dead section over the insulated over lap. This protection is provided by panto flasover Relay. viii) To detect and isolate a high resistance OHE ground fault. This fault can not be 105  detected by normal distance protection relay. Hence, a sepreate relay called Delta I relay is provided for the purpose. 5.9.2 The normal zone of a sub-station to neutral section varies from 25 to 40Km. Under emergency feed condition, however, the zone would extend upto the next sub-station by closing the bridging intrruptors at the neutral section and will be about double the zone of normal feed.It will be apparent from the impedance value given in para-4 that the fault current under such condition could be well below the traction load current. Over current or plain impedance relay which operate below a certain impedance level and which function independently of the phase angle between voltage and current, will be unable to discriminate of the argument of the impedance of given argument is required. 5.9.3 The protective system shall, therefore,comprise the following relays i) An admitance(MHo) relay to cover the zone of protection i.e. from the sub-station to the adjacent sub-station and operate for any earth fault on the overhead equipment in the zone.In order to allow for the additional impedance of booster transformers and return conductor, the relay shall have a reach of atleast 125km of single track OHE with an impedance of 0.52 ohm/km at 70 degree phase angle. ii) an admittace (MHo) relay for protection against wrong phase coupling due to phase to phase fault with 120 degree or 60 degree phase difference between two phases,with a maximum torque angle of 125 degree to 145 degree.The relay may preferably be provided with a forward offset to prevent it from operating on phase to earth faults. iii) An over current relay of instantaneous type which can clear faults between the sub- station and the section, with an adjustable current setting ranging from200%to800%. The instantaneous relays shall of 10 class with operating time not exceeding 10 ms. iv) A single shot auto reclosing relays to work in conduction with master trip relay shall be provided. v) Pantoflash over relay for protection of OHE from flasover caused by movement of pantograph from live to dead OHE across be insulated overlap provided in front of traction sub station If Nutral section is provided in front of TSS, then there is no need of panto flashover relay. vi) Delta I relay is provided for detection and clearance of high resistance earth fault of OHE (not detectable by Distance Protection Relay). 5.9.4 The relays (i), (ii), (iii), (v) & (vi) above shall trip the corresponding feeder circuit breaker in case of fault , through a high speed self reset type tripping relay to be designated as Master trip relay. 106  5.9.5 A single shot reclosing relay to work in conjunction with MasterTrip relay shall be provided.The auto-reclosing relay shall have an adjustable time setting between 0.5 sec. to 30 sec for the reclosure of the feeder circuit breaker.After single auto-reclose of the breaker it shall be possible to operate the same either manually or on remote control without any necessity for manual reset in auto-reclosing relay.This requirement as essential in view of the sub-station being unattended. 5.9.6 Suitable operation counter shall also be provided individually for distance pro- tection adittance(Mho) relay,wrong phase coupling admittance(Mho) relay, instantaneous over current relays and also for the auto-reclosing scheme. 5.9.7 In addition to the above protection an instantaneous acting undervoltage relay is provided by the purchaser to trip the bridging interruptor at the neutral section in case of undervoltage during emergency feed condition. 5.9.8 The relays shall be suitable for operation from 25KV current transformer and 25KV potential transformer to the following particulars : Rating CT PT i) Rated system voltage 25KV rising upto 30KV ii) Rated transformation 1000-500/5A 25KV/110V ratio iii) Rated burden 60VA 100VA iv) Rated accuracy limit lactor 15 -- iv) Accuracy class 5P as per 1.0/3P as IS:2705 PER IS:3156 (PTIII) (pt.II & III) 1981 1978 5.9.9 The relay shall conform to the accuracy class 15 as per IS 3231-1965 5.9.10 The operating time for the Mho relay shall be as small as possible and shall not exceed 20ms for a source to line impedance ratio of 1:1 in case of earth fault relays. The operating times for minimum and maximum setting of the relays in term of distance shall be furnished by the tenderer together with the variation in operating time for various fault positions expressed as percentage of relay settings. 5.9.11 The polarizing input for relays shall have a tuned memory circuit ,so that it is possible to maintain a polarizing signal even after a fault occur , for a sufficiently long time for the operation of relay to operate in case of a fault close to the sub-station, when the restaining voltage disappears. 5.9.12 The relays shall be insensitive to power swing, heavy overload and transient condition including magnetizing in rush current of locomotive to transformers and shall be suitably designed to compensate the effect of fault arc resistance. 107 108  Table 9.2 Electro-static induction due to 25KV as traction (The changed conductor is assumed to be at a height of 6m above rail level) Length of parallelism of aerial conductor in km 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000 1.500 2.000 Distance of the conductor from the Discharge current in milli-ampere catenary(m) 08 0.95 1.89 2.84 3.79 4.74 5.69 6.64 7.58 8.53 9.40 14.5 18.9 10 0.72 1.43 2.14 2.86 3.58 4.28 5.01 5.73 6.44 7.16 11.0 14.5 12 0.56 1.11 1.66 2.22 2.78 3.33 3.89 4.44 5.00 5.56 8.5 11.0 14 0.44 0.88 1.32 1.76 2.20 2.64 3.08 3.52 3.96 4.40 5.5 9.0 16 0.36 0.72 1.08 1.44 1.80 2.16 2.52 2.88 3.24 3.66 5.5 7.5 18 0.30 0.59 0.89 1.18 1.48 1.77 2.07 2.37 2.66 2.96 4.5 6.0 20 0.25 0.50 0.74 0.99 1.24 1.49 1.74 1.98 2.23 2.48 3.5 5.0 Length of parallelism of aerial conductor in Km 2.500 3.000 3.500 4.000 4.500 5.000 5.500 6.000 6.500 7.000 7.500 Distance of the conductor from Discharge current in milli-ampere the catenary(m) 08 23.7 28.5 33.0 38.0 42.5 47.5 52.5 57.0 62.0 66.5 71.0 10 18.0 21.5 25.5 28.0 32.0 36.0 40.0 43.0 46.5 50.5 53.5 12 14.0 16.5 19.5 22.0 25.0 28.0 30.5 33.5 36.0 39.0 41.5 14 11.0 13.5 15.5 17.5 20.0 22.0 24.0 26.0 28.5 31.0 33.0 16 9.0 11.0 12.5 14.5 16.0 18.0 20.0 21.6 23.5 25.0 27.0 18 7.5 9.0 10.5 12.0 13.5 15.0 16.5 18.0 19.0 21.0 22.0 20 6.5 7.5 8.5 10.0 11.0 12.5 13.5 15.0 16.0 17.5 18.5 109