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Table 2.31. Basic Data Example 1.Highest voltage for equipment Um k V rms 145Corresponding line to (ground) neutralU m voltage k V rms 83.72 3 Corresponding Temporary over voltage(derived from system studies)This voltage is high in step up sub stationsdue to load rejection i.e. 1.5 per unitk V rms 104.652.Minimum safety factorFor lightning overvoltagesRepresentative Characteristics ofSurge Diverter (obtain frommanufacturer)Rated Voltage (nearest available above125 x 104.65)Maximum lightning impulse spark overvoltageMaximum front-of-wave impulse sparkover voltageMaximum residual impulse spark overvoltage3 Protection Levels1.25kV rms 140kV 415kV 470kV 405To lightning impulse kV 4154 Insulation level (phase to earth)Lightning ImpulseMinimum lightning impulse voltage kV 415Rated lightning impulse voltage as perIS:Ratio of the rated lightning impulsevoltage to the lightning impulseprotective levelkV 550kV 1.321-5
2.3.4 Existing Insulation Practice of Substation EquipmentsThe substation equipments namely the power transformers circuit breakers anddisconnecting switches are considered for detailing the existing practice.Existing PracticeThe commonly adopted insulation levels at present for the above mentioned equipmentsare given in table 2.4 with reference to Karnataka and Tamil Nadu (66 kV, 110 kV and220 kV) and Punjab (132 kV Bhakra System).A commonly adopted practice is to locate lightning arrester as near to the transformer aspossible. In large substations additional arresters could be required at suitable locations toprotect circuit breakers, isolators and other equipments. Since each of these equipmentscannot be provided with arrester individually, it is the normal practice to adopt higherinsulation to provide the equipment with as good protection as is economically justified.Insulation level for circuit breaker and other equipments connected to the busbar togetherwith the bubars themselves are designed for insulation class about 10% higher than theinsulation level for the transformers (one class higher). Insulation level across the openpoles of the isolating switches is kept about 10 to 15 % higher than that provided betweenthe poles and the earth, so that in the event of a surge at an open isolating switch, theflashover should pass to earth and not across open poles.Table 2.4: Insulation Levels of the terminal Equipments RecommendedS. DescriptionNo.1. Highest systemvoltage kV (rms)2. Power transformerinsulation levels kV(Crest)3. Circuit breaker kV(Crest)4. Disconnectingswitches between poleand earth kV (Crest)Nominal voltage in kV220 132 110 66 33 11245 145 123 72.5 35 12900 550 450 325 170 751050 650 550 350 170 751050 650 550 380 170 752.3.5 Protection with Spark GapsThe spark gap is among the cheapest protective devices used for diverting the surgesfrom line to earth. After the break down of the spark gap the circuit breaker alwaysoperates to interrupt the fault of power frequency current in the circuit. Thus theoperation of the gap generally results in the circuit outage and interruption of supply ofthe power system. It is therefore used as a back up to surge arrestor (lightning arrestor).1-6
Page 2 and 3: Section -1Guide for Design of Outdo
Page 4 and 5: The terms atmospheric overvoltages
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 32 and 33: 4.6 TestsThe CTs shall be provided
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
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8.10 Parallel OperationThe transfor
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(a)(b)33 kV Transformers (MVA)1.001
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(e)(f)(g)(h)(i)(j)(k)(l)(m)(n)(o)(p
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18.0 Oil Containment and Fire Prote
Page 67 and 68:
) The limits of temperature rise me
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Example Calculation -1Generator Tra
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TRANSFORMER RATING AND CHARACTERSTI
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3.0 Type of Circuit BreakerFollowin
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iii) during arcing of SF6 breaker,
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3.4 Protection Classes for Switchge
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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
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5.17 Rated time quantities and oper
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25405017.5 812.516254024 812.516254
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component of fault current in addit
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Steps involved in applying method a
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to earthxvii. Difference in the ins
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Datai) Sub transient reactance of g
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Annexure-1Current waveAA = envelop
Page 99:
Annexure-3Fig. 3.3 Arc extinction4-
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