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4.6 TestsThe CTs shall be provided with bolted type terminals to receive ACRS conductors upto15 mm dia (without requiring use of lugs) both in vertical and horizontal directions. Theterminals shall be such as to avoid bimetallic actions.Each current transformer should comply with type and routine test including short timecurrent test as stipulated in relevant Indian Standard specification.4.7 External Insulation (12 kV & Above)The external insulation should comprise of a hollow porcelain, which will also serve as ahousing for the main insulation or other internal parts of the CTs. Insulators should be ofhigh grade and homogeneous procelain made by the wet process. The poreclain shouldhave hard glazing and should comply with the requirements of IS 5621 in all respects.The skirt forms should be carefully selected to achieve the necessary flashover distanceand total / protected creepage distances as required.4.8 Fittings and Accessories (12 kV & Above)1. Primary terminals2. High frequency current surge divertors3. Terminal connectors for connections from line to the CT primary4. Oil level gauge5. Pressure relief device6. Expansion chamber or other suitable type of device for absorbing variations in thevolume of oil due to change of temperature.7. Weather proof secondary terminal box fitted with door and complete withterminals and shorting links.8. Lifting lugs9. Fixing lugs with bolts, nuts and washers for holding down the CTs on thesupporting steel structures.10. Rating and diagram plates11. First filling of oil12. Oil filling plug and drain valve13. Earthing terminals5.0 Potential Transformer and Coupling Voltage Transformera) 33 kV & AboveThe voltage transformer may be either of the electro-magnetic type or the capacitor type.The electro-magnetic type VTs are costlier than the capacitor type and are commonlyused where higher accuracy is required as in the case of revenue metering. For otherapplications capacitor type is preferred particularly at high voltages due to lower cost andit serves the purpose of a coupling capacitor also for the carrier equipment. For groundfault relaying an additional core or a winding is required in the Voltage transformers2-10
which can be connected in open delta. The voltage transformers are connected on thefeeder side of the circuit breaker. However, another set of voltage transformer is normallyrequired on the bus-bars for purpose of synchronization. Potential transformer class andratio is determined by electrical protection, metering consideration.b) 12 kVThe voltage transformer shall of outdoor, 3 phase either oil filled or resin cast type, whichThe voltage transformers shall be of outdoor, 3 phase either oil filled or resin cast type,which shall be enclosed in a weather-proof housing to avoid direct exposure to sun andother atmospheric influences. The incoming and outgoing terminals shall be brought outthrough suitable porcelain bushings. The voltage transformer shall be suitable foroperation in a solidly grounded system.5.1 Type and Rating of Potential TransformerPotential transformer, design, Temperature rise and testing etc. should be in accordancewith IEC: 186, IS: 3156 (Part I & II).The PTs should be single phase oil immersed self cooled type suitable for outdoorinstallation of kV class required. The core should be of high grade non ageing electricalsilicon laminated steel of high permeability. The PTs sealed hermetically scaled toeliminate breathing and prevent air and moisture entering the tank. Oil level and pressurereleasing device etc. should be provided.Each potential transformers should have the following (table 2.5.1) particulars under thesite conditions for the system under design (typical values for 72.5 kV system are given).1. Rated voltage 72.5 kV 36 kV 12 kV2. Rated frequency 50 Hz 50 Hz 50 Hz3. Accuracy class of winding 1.0 1.0 1.04. Voltage ratio 66 kV/3/110V/3 33 kV/3/110V/3 11 kV/3/110V/35. Grade of oil As per IS: 3356. Maximum phase angle error 40 min. 40 min. 40 min.with 25% and 110% of ratedburden at 0.8 p.f. lagging atany voltage between 80% and120%7. Temperature rise at 1-1 times As per IS: 3156 As per IS: 3156 As per IS: 3156rated voltage with rated burden(OC)8. Rated voltage factor & time Continuous 1.2 Continuous 1.2 Continuous 1.29. 1 minute power frequency(wet/dry) withstand testvoltage30 sec. – 1.5 30 sec. – 1.5 30 sec. – 1.5140 kV r.m.s. 75 kV r.m.s. 28 kV r.m.s.2-11
Page 2 and 3: Section -1Guide for Design of Outdo
Page 4 and 5: The terms atmospheric overvoltages
Page 6 and 7: Table 2.31. Basic Data Example 1.Hi
Page 8 and 9: Spark gaps specified for fitting to
Page 10 and 11: 2.4.2 Working Safety Clearances125
Page 12 and 13: Highest System Voltage rating kV Sp
Page 14 and 15: 2.6 Insulator TypeTypes of insulato
Page 16 and 17: Bending .. .. 1265 kg/sq.cm.Shear .
Page 18 and 19: v) Installations in difficult site
Page 20 and 21: During maintenance, it is essential
Page 22 and 23: Areva Compact Air Insulated Substat
Page 24 and 25: The bus bar sizes should meet the e
Page 26 and 27: disconnect switch contacts in such
Page 28 and 29: (iv)Electro magnetic type interlock
Page 30 and 31: ) Temperature rise of 11 kV Class C
Page 34 and 35: 10. 1.2/50 micro seconds impulse 32
Page 36: 7.0 Lightning ArrestorsLightning ar
Page 39 and 40: and this aspect has to be kept in m
Page 41 and 42: Fig. 12.1: Layout of 12 kV Agnoor S
Page 43 and 44: Fig. 12.4 Layout of 72.5 kV Switchy
Page 45 and 46: 464006800 7600 3000LA30002000 2000X
Page 47 and 48: Fig. 12.6:145 kV Outdoor Switchyard
Page 49 and 50: Fig. 12.7: 245 kV Outdoor Switchyar
Page 51 and 52: 2-20
Page 53 and 54: 3.0 Transformer RatingThe full load
Page 55 and 56: OFAFOil Immersed with forced oil ci
Page 57 and 58: The transformer may be operated wit
Page 59 and 60: 8.10 Parallel OperationThe transfor
Page 61 and 62: (a)(b)33 kV Transformers (MVA)1.001
Page 63 and 64: (e)(f)(g)(h)(i)(j)(k)(l)(m)(n)(o)(p
Page 65 and 66: 18.0 Oil Containment and Fire Prote
Page 67 and 68: ) The limits of temperature rise me
Page 69 and 70: Example Calculation -1Generator Tra
Page 71 and 72: TRANSFORMER RATING AND CHARACTERSTI
Page 73 and 74: 3.0 Type of Circuit BreakerFollowin
Page 75 and 76: iii) during arcing of SF6 breaker,
Page 77 and 78: 3.4 Protection Classes for Switchge
Page 79 and 80: The rated voltage is expressed in k
Page 81 and 82: 5.7 Rated Short Circuit Making Curr
Page 83 and 84:
Effect of circuit conditions on rec
Page 85 and 86:
5.17 Rated time quantities and oper
Page 87 and 88:
25405017.5 812.516254024 812.516254
Page 89 and 90:
component of fault current in addit
Page 91 and 92:
Steps involved in applying method a
Page 93 and 94:
to earthxvii. Difference in the ins
Page 95 and 96:
Datai) Sub transient reactance of g
Page 97 and 98:
Annexure-1Current waveAA = envelop
Page 99:
Annexure-3Fig. 3.3 Arc extinction4-
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