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water8 Protection against indefineimmersion in water4.0 Rated CharacteristicsThe main characteristics of a power circuit breaker including its operating devices andauxiliary equipment used to determine the rating are as follows:-Rated voltageRated insulation levelRated frequencyRated normal currentRated short-time withstand currentRated short-circuit breaking currentRated short-circuit making currentRated operating sequence (duty cycle)Rated transient recovery voltage (TRV) for terminal faultTotal breaking time (maximum)Rated characteristics for short-time faults, for three pole circuit breakers designedfor direct connection to overhead transmission lines and rated at 52 kV and aboveand at more than 12.5 kA rated short breaking currentIn addition, the following characteristics are necessity for specific application.Rated line charging breaking currentRated inductive breaking currentRated capacitor breaking currentRated out of phase breaking current5.0 Standard Ratings of Circuit Breakers5.1 Rated Voltage: Voltage rating of the power circuit breaker is in terms of threephase line to line voltage of the system. The rated voltage of the circuit breaker should beof standard rating chosen so as to be at least equal to the highest voltage of the system atthe point where the circuit breaker is to be installed. The operating voltage and the powerfrequency recovery voltage should not exceed the rated maximum values because thismaximum is upper limit for continuous operation.It is however considered that operation at altitude above 1000 meters should be givenspecial considerations and certification from manufacturer be obtained because ofpossible influence of altitude on interrupting capacity.In case of generator circuit breakers the rated maximum should be equal to the maximumoperating voltage of the generator, which is usually equal to 1.05 times rated voltage.4-7
The rated voltage is expressed in kV (rms) and refer to phase to phase voltage.Nominal system voltagekV rmsRated voltage of circuit breakerkV rms11 1222 2433 36132 145220 2455.2 Rated Insulation Level: - Insulation level of power circuit breakers should beselected from standard insulation level listed in IS: 13118. Refer table 2.1 (section-1) forvoltage upto 36 kV and table 2.2 (section-1) for voltages upto 245 kV. For insulation coordinationrefer (Para 2.3.4. of section1).The surge protection of the system should be coordinated with the impulse strength of thebreaker, both across the open contacts and to ground. Attention should also be given toincrease in surge voltage because of reflections which occur at breakers when theircontacts are open, especially where cables are involved.Surge arrestors are generally installed on the bus or on transformers and not on eachcircuit breaker, the surge voltage at the breaker can exceed that at the arrestors. Theamount of the excess depends upon the steepness of the wave front and the distance fromthe circuit breaker to the surge arrestors. When the circuit breaker is in the open position,either intentionally left open or during operation, an incoming surge voltage may bedoubled by reflection at the open contacts. Selection of too low an insulation level forcircuit breakers, if not individually protected by arrestors, may result in line-to-ground, oropen gap insulation failure of the circuit breaker. Use of individual line entrance surgearrestors may be required if the lightning trip-out rate of the line exceeds 1 per year (referIEEE std. 37.010-1999). Refer section 1 for more details.5.3 Rated Frequency: standard power circuit breakers are rated at 50 cycles. Serviceat other frequencies requires special consideration.5.4 Rated Normal Current: rated normal current of a circuit breaker is the rms valueof the current which the circuit breaker shall be able to carry continuously at ratedfrequency. With the rise in temperature of its different parts not exceeding specifiedvalues. Values of rated normal currents should be selected from standard value of normalcurrents as per IS: 13118 which are 400A; 630A; 800A; 1250A; 1600A; 2000A; 2500A;3500A; 4000A; 5000A; 6300A (if required higher values can be selected). These ratingsare based on operation of the circuit breaker or switchgear assembly where the ambienttemperature (measured outside the enclosure) does not exceed 40 0 C and the altitude doesnot exceed 1000 m. Standard equipment may be operated at higher altitude by reducingthe continuous current rating in accordance with the following tables (based on AmericanPractice).4-8
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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
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
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: 3.4 Protection Classes for Switchge
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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