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Altitude in meters (approx.) Insulation level Rated continuouscurrent1000 m 1.00 1.001500 m 0.95 Refer to manufacturer3000 m 0.80 Refer to manufacturerThe rated continuous current is based on the maximum permissible total temperaturelimitations of the various parts of the circuit breaker when it is carrying rated current atan ambient temperature of 40 0 C.When the ambient temperature is greater than 40 0 C, the current must be reduced to lessthan rated continuous current to keep temperatures within allowable limits.5.5 Rated short-time withstand currentRated short-time withstand current is equal to the rated short circuit breaking current. Therated peak withstand current is equal to rated short circuit making current. Rated durationof short circuit should be as per IS 13118.5.6 Rated Short Circuit Breaking CurrentThe rated short circuit breaking current is the highest short circuit current which thecircuit breaker will be capable of breaking in a circuit having power frequency recoveryvoltage corresponding to rated voltage and transient recovery voltage (refer Para 3.5.7)equal to the rated value of the circuit breaker as specified in IS. For three pole circuitbreakers the AC component relates to three phase short circuit including short line fault.Rated short circuit breaking current is characterized by two values Fig. 1 (Annexure-1).i) rms value of AC component and is termed rated short circuit currentii) Percentage DC componentrms value of AC component of the rated short-circuit breaking current should be selectedfrom standard values given in IS 13118. Percentage DC component is dependant upon thetime from initiation of short circuit current and standard values are given in IS 13118.The standard values practice of breaking current or being 6.3 kA, 8 kA, 10 kA,12.5 kAkA,16 kA, 20 kA, 25 kA, 31.5 kA, 40 kA, 50 kA, 63 kA, 80 kA, 100 kA. The earlierpractice was to express the rated breaking capacity in MVA.MVA : 3 kV kAMVA : breaking capacity of circuit breakerkV : rated voltagekA ; rated breaking current4-9
5.7 Rated Short Circuit Making CurrentThe circuit breakers some times, close on to a existing fault. In such cases, the currentincreases to the maximum values as the peak of first current loop. The circuit breakermust be able to close without hesitation as contacts touch. The circuit breaker must beable to withstand the high mechanical forces during such closure.As per IS: 13118 rated short circuit making current should be at least 2.5 times the rmsvalue of the A. C. component of its rated short circuit breaking current.5.8 Transient Recovery Voltage and Restriking Voltage and First Pole to clear FactorThe instantaneous value of the recovery voltage at the Instant of arc extinction is calledthe active recovery voltage figure 3.3 (Annexure-3).5.9 Rated Transient Recovery Voltage (TRV) for terminal faults:- The rated transientrecovery voltage (TRV) for terminal faults relating to the rated short-circuit breakingcurrent is the reference voltage. This constitutes the limit of the prospectivetransient recovery voltage of circuits, which the circuit breaker will be capable ofbreaking in the event of a short circuit at its terminals.Wave form of transient recovery voltage varies according to the arrangement ofcircuit.actualStandard value of rated TRV for 3 pole circuit breaker as per in IS: 13118 for the circuitbreakers used in the outdoor substations under consideration are given below table 3.2.Table 3.2RatedvoltageFirst pole toclear factorTimeTRVPeakvalueRaterise(kV) (s) (kV) (kV/μs)3.3 1.5 40 6.2 0.157.2 1.5 52 12.3 0.2412 1.5 60 20.6 0.3436 1.5 108 62 0.5772.5 1.5 166 124 0.75145 1.3 77 215 2.0145 1.5 89 249 2.0245 1.3 130 364 2.0ofRemarks4-10
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Section -1Guide for Design of Outdo
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The terms atmospheric overvoltages
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Table 2.31. Basic Data Example 1.Hi
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Spark gaps specified for fitting to
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2.4.2 Working Safety Clearances125
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Highest System Voltage rating kV Sp
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2.6 Insulator TypeTypes of insulato
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Bending .. .. 1265 kg/sq.cm.Shear .
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v) Installations in difficult site
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During maintenance, it is essential
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Areva Compact Air Insulated Substat
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The bus bar sizes should meet the e
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disconnect switch contacts in such
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(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
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: The rated voltage is expressed in k
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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