S&C Instruction Sheet 695-545
23
Appendix A
WARNING
Aging, damage, or electrical or mechanical wear may
reduce the VLF ac withstand capacity of the switch-
gear. Therefore, the ac test voltage must be selected
such that it does not exceed the withstand limits of the
switchgear.
Application of ac test voltage greater
than the withstand capability of the switchgear
can result in a flashover, injury, and equipment
damage.
DANGER
Do not exceed the test voltages given in Table 3.
Exceeding the test voltages can cause a flashover of
the isolating gap or phase-to-phase insulation of the
switchgear.
This can lead to a power-frequency
fault in the gear or the VLF test source, and result
in severe personal injury or death.
WARNING
When testing cables connected to energized switch-
gear, proper isolation of the power-frequency source
from the VLF test source must be maintained. Follow
the recommendations provided by the manufacturer
of the VLF test equipment. Follow the user’s operat-
ing and safety procedures for grounding the cable,
connecting the VLF test source, isolating the VLF test
source (in case of flashover), ungrounding the cable,
applying the VLF test source, discharging the cable,
and regrounding the cable.
WARNING
When VLF cable testing has been completed or has
been interrupted, you must discharge the cable sys-
tem and the test equipment. Allow the time needed to
fully discharge the cable system and test equipment.
Failure to fully discharge the cable system and test
equipment can result in serious damage to the cable
system and test equipment.
Table 3. Vista SD Switchgear Very Low Frequency
(.01- to 1-Hz) Sinusoidal Waveform Maximum Test
Voltages
Vista SD
Switchgear
System
Class, kV
Acceptance Test
(phase to ground)
Maintenance Test
(phase to ground)
kV, RMS
kV, Peak
kV, RMS
kV, Peak
15.5
23
33
19
26
27
36
51
27
38
Fault-Interrupter Testing
When performing dielectrical tests on Vista SD Underground
Distribution Switchgear, the vacuum fault interrupters will
not be subject to voltage across the open gap because the
disconnect switch isolates the vacuum interrupters from
the test voltage. Because the vacuum interrupter will not
be energized across the open gap, there is no exposure to
the X-rays normally associated with high-voltage testing
of vacuum devices. Routine testing of the vacuum fault
interrupters is not recommended. For those users who
desire to test the vacuum interrupters, contact the nearest
S&C Sales Office for specific instructions.
