26 S&C Instruction Sheet 681-510
Dielectric Testing
Vista switchgear has been designed to allow dc testing
of the cables with the other ways of the gear energized.
The integral GROUNDING switch may be used to ground
the cable. After testing, the dc test equipment should be
used to discharge any stored charge on the cable before
regrounding with the GROUNDING switch. The dc test
voltages and dc cable thumping voltages should not exceed
the voltages given in Table 2.
WARNING
When it is necessary to test the cables connected
to a unit of ener gized switchgear, proper isolation of
the power-frequency source from the dc test source
must be maintained. Follow the recommen dations by
the manufacturer of the dc test equipment or fault-
locat ing equipment. The user’s operating and safety
procedures should be followed for grounding the
cable, connecting the dc test source, isolating the dc
test source (in case of flashover), ungrounding the
cable, applying the dc test source, discharging the
cable, and regrounding the cable.
Table 2. Maximum Cable Test and Cable Thumping
Voltages
Vista Switchgear Rating, kV
Dc Cable
Test Voltage,
kV
Dc Cable
Thumping
Voltage, kV
①
50 Hertz
60 Hertz
Impulse (BIL)
12
15.5
95
30
15
24
27
125
40
20
36
38
150
40
20
①
The dc cable thumping voltage is 50% of the dc cable test voltage
because of voltage doubling that will occur at the open end of the cable
which is assumed to be a unit of Vista switchgear. If the open end of the
cable is grounded, the dc cable thumping voltage applied to the cable
and switchgear can be increased to the dc cable test voltage.
Fault-Interrupter Testing
When performing dielectric tests on Vista switchgear, the
vacuum fault interrupters will not be subject to voltage
across the open gap because the disconnect switch will
isolate the vacuum interrupter from the test voltage.
Because the vacuum interrupter will not be ener gized
across the open gap, there is no expo sure to X-rays
normally associated with high-voltage testing of vacuum
devices. Routine testing of the vacuum fault interrupt ers
is not recommended. For those users who desire to test
the vacuum interrupters, contact the nearest S&C Sales
Office for specific instructions.
①
The dc cable thumping voltage is 50% of the dc cable test voltage because
of voltage doubling that will occur at the open end of the cable which is assumed
to be a unit of Vista switchgear. If the open end of the cable is grounded, the dc
cable thumping voltage applied to the cable and switchgear can be increased to
the dc cable test voltage.
