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elaying. The dead-tank breaker does require additional insulating gas to provide theinsulation between the interrupter and the grounded tank enclosure.Live-tank circuit breakers consist of an interrupter that is mounted on insulators and is atline potential. This approach allows a modular design as interrupters can be connected inseries to operate at higher voltage levels. Operation of the contacts is usually through aninsulated operating rod or rotation of a porcelain insulator assembly by an operator atground level. This design minimizes the quantity of gas used for interrupting the arc as noadditional quantity is required for insulation of a dead-tank enclosure. The design alsoreadily adapts to the addition of pre-insertion resistors or grading capacitors when theyare required. Seismic capability requires special consideration due to the high center ofgravity of the interrupting chamber assembly.Interrupting times are usually quoted in cycles and are defined as the maximum possibledelay between energizing the trip circuit at rated control voltage and the interruption ofthe main contacts in all poles. This applies to all currents from 25 to 100% of the ratedshort circuit current.Breaker ratings need to be checked for some specific application. Applications requiringreclosing operation should be reviewed to be sure that the duty cycle of the circuitbreaker is not being exceeded. Some applications for out –of- phase switching or back-tobackswitching of capacitor banks also require review and may require specific dutycircuit breakers to insure proper operation of the circuit breaker during fault interruption.3.1 Vacuum Circuit BreakerVacuum circuit breakers use an interrupter that is a smaller cylinder enclosing themoving contacts under a high vacuum. When the contacts part, is a formed from contacterosion. The arc products are immediately forced to and deposited on a metallic shieldsurrounding the contacts. Without anything to sustain the arc, it is quickly extinguished.Vacuum circuit breaker are widely employed for metal-clad switchgear up to 36 kV class.The small size of the breaker allows significant savings in space and material comparedto earlier designs employing air magnetic technology. When used in out door circuitbreaker designs, the vacuum cylinder is housed in a metal cabinet or oil filled tank fordead tank construction.3.2 Advantages and DisadvantagesAdvantages: Advantages of SF6 breakers over the conventional breakers is given below:i) due to outstanding arc quenching property of SF6, the arcing time is very small.This reduces contact erosion.ii) using SF6 gas at low pressure and low velocity; the current chopping can beminimized.4-3
iii) during arcing of SF6 breaker, no carbon dioxide is formed and hence no reductionof dielectric strength.iv) SF6 breaker is silent in operation and moisture ingression into the gas cycle isalmost nil.v) SF6 breaker performance is not affected due to variation in atmosphericconditions.vi) SF6 breaker is compact in size and electrical clearances are drastically reduced.Disadvantages: The only disadvantage of using SF6 to some extent is suffocation. Incase of leakage in the breaker tank, this gas, being heavier than air settles in thesurroundings and may lead to suffocation of the operating personnel. However, it isnon-poisonous.3.3 Evaluation of SF6 and Vacuum Switching TechnologiesSI. No.1Criteria2SF 6 circuit breaker3Vacuum circuit breaker4I. SWITCHING DUTIES1. Summated breakingcurrent capacity2. Critical switchingi. Motor, Reactors smallinductive current.ii. Capacitorsiii. Over head and cablefeeders.iv. Switching of arcfurnaces.3. Suitability of single andmulti shot auto reclosecycles.To 50 times rated short circuitbreaking current To 10,000 timescontinuous rated current.Very well suited Over voltagegenerally under 2.5 p.u. Normallyno action necessary to limit overvoltages.Well suited. Restrike free. In specialcases reactors may be necessary tolimit in rush current - Low overvoltage.Very well suited-Restrike free.Only suitable in applicable withcomparatively low number ofoperations per day.Very well suitedTo 100 times rated short circuitbreaking current To 20,000times continuous rated current.Well suited. Under certaincircumstances steps may benecessary to limit over voltagesbecause of possibility of virtualcurrent chopping. Use of surgearresters recommendedSuited. Generally Restrike free.In special cases reactors may benecessary to limit in rushcurrent-Reignition and restrikespossible in certain cases due tostatistical scatter of breakdownvoltage in vaccum.Very well suited Restrike free.Suitable also for applicationswith very high number ofoperations (over 100 co-per day.Very well suited.SI. No.1Criteria2SF 6 circuit breaker 3Vacuum circuit breaker4II. MAINTAINABILITY4-4
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
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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
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: 3.0 Type of Circuit BreakerFollowin
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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