Testing of metal-enclosed switchgear assemblies 14/423

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0.48 0.6 4.16

Table 14.2 For series II voltage systems Insulation levels, power frequency and impulse withstand voltages for metal-enclosed switchgear assemblies

b c b C b c

- - - 0.508 2.2 3.1 - 0.635 2.2 - - - 3.1 - 4.16 19.0 19 60 60 21 21

Rated maximum , system voltage Standard lightning impulse (1.2/50 p ) voltage withstand (phase to ground)

4

One-minute d.c. voltage withstand (phase to ground)

5

Nominal system voltage

One-minute power frequency voltage withstand at a frequency not less than the rated 60 Hz (phase to ground) 3 I 2

kV (r.m.s.) kV (r.m.s)

1.2a 13.8 14.4

8.25 15.0 1 15.5

36.0 26.0 36.0 36.0 - 50.0

95 75 95 95 - 110

50 31 50 IO

23.0 34.5 69.0

1 :::: 72.5

- 60.0 80.0 80.0 - 160.0

- 125 150 150 - 350

aANSI C-37/20C specifies this rating only for metal-clad switchgear assemblies and not for metal-enclosed bus systems. bWith breaker assemblies ‘With isolator assemblies Based on ANSI C-37/20C

Notes 1 (a) The procedure for a d.c. test is same as for a.c. Due to variable voltage distributions when conducting d.c. tests, the ANSI Standard

recommends that the matter may be referred to the manufacturer for system voltages 25.8 kV and above. (b) For a power frequency voltage withstand test, the d.c. test is generally not recommended on a.c. equipment, unless only d.c. test

voltage is available at the place of testing. The d.c. test values, as provided above, are therefore for such cases only and are equivalent to power frequency a.c. voltage withstand test values.

Power frequency tests after erection at site, if required, may be conducted at 75% of the values indicated above. Also refer to field tests (Section 14.5, Table 14.8).

2

Table 14.3 For series I voltage systems. Dielectric test voltages for control and auxiliary circuits and also LT power circuits

( i ) For fixed as well as draw-out assemblies The trolley is in the service position in draw-out assemblies (Section 13.3.2). ~

Nominal auxiliary/power voltage

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One-minute power frequency voltage withstand at any frequency between 45 and 65 Hz (between phases and ground)

1 Between phase to phase and each phase to ground with the switching devices in the closed position

2 Between phase to phase and each phase to ground with the switching devices in the open position. This test is to be conducted on both line and load sides of the switching device.

3 Between the line and the load terminals of each phase, the main switching devices being in the open position.

Control and auxiliary circuits 1 Where the rated insulation

voltage does not exceed 60 V 1000 V (r.m.s.)

2 Where the insulation voltage (2 V, + 1000) volts with a minimum of 1500 V (r.m.s.). exceeds 60 V

Power circuits 3 For voltages between 300

and 660 V 2500 V (rms) ( i i ) For draw-out assemblies

The trolley is in test position and the main switching device in the closed position, As in IEC 60439-1

1 Between phase to phase and each phase to ground on both line and load fixed terminals.

2 Between line and load fixed terminals of each phase. ANSI-C37/20C recommends this test to be conducted at a value 10% higher than specified in Table 14.2 for both power frequency and impulse voltage withstand tests.

raised gradually but rapidly and then maintained at that level for one minute, reduced rapidly up to 50% of its value and then disconnected.

5 During the test, one pole of the testing transformer should be connected to ground and the frame of the assembly.