Contents
Voltage Class and Insulation Level


Rated insulation levels for various highest system voltages from 0.66 kV to 765 kV have been detailed in I.S. 2705/1992 Part I in tables 1A, 1B and 1C. These tables are reproduced below for ease of reference.

                                                                                 

                 Table 1A Rated insulation levels for
  Highest System Voltages upto and including 72.5 kV.
 

Nominal

Highest

Power

Lightning

System

System

Frequency

Impulse

Voltage

Voltage

Withstand

Withstand

kV (rms)
kV (rms)

VoltagekV (rms)

Voltage kV (peak)

     
List 1
List 2
Upto 0.60
0.66
3
-
-

3.3

3.6
10
20
40
6.6
7.2
20
40
60
11
12.0
28
60
75
15
17.5
38
75
95
22
24.0
50
95
125
33
36.0
70
145
170
45
52.0
95
250
250
66
72.5
140
325
325

                                                                       
                              Table 1B Rated insulation levels for
  Highest System Voltages upto and includ Upto and including 245 kV

Nominal

Highest

Power

Lightning

System

System

Frequency

Impulse

Voltage

Voltage

Withstand

Withstand

kV (rms)
kV (rms)

VoltagekV (rms)

Voltage kV (peak)

110
123
185
             450
 
230
550

132

145
230
5650
275
6850
220
245
360
850
395
950
460
1050

 

Table 1C

Rated insulation levels for

Highest System Voltage of 420 kV and above.


Nominal

Highest

Power

Switching

System

System

Frequency

Impulse

Voltage

Voltage

Withstand

Withstand

kV (rms)
kV (rms)

VoltagekV (rms)

Voltage kV (peak)

400
420
1175
             950
 
1300
1050

 

1425
1050
525
525
1425
1050
1550
1175
765
765
1800
1300
   
2100
1425
2400
1550

It is indicated in I.S.2705 (Part I)/1992 (Note appended to clause 8 page 6) that the H.S.V., Power frequency voltage withstand test level and the Lightning impulse voltage withstand test level be indicated as H.S.V./ Power frequency Withstand Voltage/Lightning Impulse Withstand Voltage e.g. for C.T. suitable for H.S.V. of 145 kV the insulation level may be indicated as 145/275/650 kV.