standards / manuals / guidelines for small hydro development - AHEC

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Spark gaps specified for fitting to the bushings of power transformers, potential andcurrent transformers, rated 66 kV and above.The spark gaps are to conform to the following specification, to prevent any damage tothe bushing due to the flashover gazing the petticoats of the bushing:a) The rods are to be circular not less than 12 mm diameterb) The rods should overhang their supports at-least one half of the gap spacing.c) The rods should be mounted so as to give a height of 1.3 times the gap spacingplus 100 mm (4 inches) above the ground plane as shown in fig. 2.3.5.Fig. 2.3.5The gap setting furnished below are adopted for all stations whether lightning arrestersare provided or not.Spacing for standard rod-gaps is given in table 2.5 (TNEB Practice).Highest systemvoltage kV rmsU mTable 2.5Critical Flashovervoltage 1/50 microsecondmkV Peak 23 Spacing of Standard Rod GapU Positive Polarity Negative Polarity72.5 59.1 7.7 6.5123 100.4 12.4 10145 118.3 15.4 13245 200 28.0 23Note: - The spacing given above are for the standard atmospheric conditions viz:1-7
Barometric pressure = 760 mm Hg.Temperature = 20 0 CHumidity= 11 grams of water vapour per cubic meter.For non-standard atmospheric conditions the spacing to give the critical flash overvoltage should be modified by dividing the above spacing by ‘d’ where:d =P0 .386 273 tP = barometric pressure in mm Hg.and t = temperature in 0 C.When the humidity differs the standard spacing should be increased by 1% for eachgramme per cubic meter below the standard value and decreased by 1 % each grammeper cubic meter above the standard.2.4 Electrical Clearances for Installing Equipment in the FieldSpace requirements and layout of electrical equipment in switchyard depends uponvarious types of air clearances required to be provided for laying the equipment ofdifferent rated voltages. Following basic clearances govern the sub-station design.(i) Earth clearance i.e. phase to ground clearance.(ii) Phase clearance i.e. phase to phase clearance.(iii) Safety clearance i.e. (a) Ground clearance.(b) Section clearance.2.4.1 Co-relation between insulation Level and minimum Phase to earth ClearancesMinimum clearances in air between live conductive parts and earthed structures to securea specified impulse withstand voltage for dry conditions as per IS 3716-1978 are given intable 2.6.These minimum clearances are valid for altitudes not exceeding 1000 m and do notinclude any addition for construction tolerances, effect of short circuits, safety ofpersonnel etc. these clearances are suitable for general application, providing as firstapproximation.Table 2.6: Correlations between Insulation Levels and Minimum Phase-to-Air Clearances as per IS: 3716 - 1978EarthRated Lightning Impulse WithstandVoltage (kV)Minimum Phase-to-Earth Air Clearances(mm)45 6060 9075 12095 1601-8
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 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
Page 59 and 60:
8.10 Parallel OperationThe transfor
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(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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