S&C Instruction Sheet 695-510
27
Appendix A
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
WARNING
Aging, damage, or electrical or mechanical wear may
reduce the VLF ac withstand capacity of the switchgear .
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 with-
stand capability of the switchgear can result in a
flashover, injury, and equipment damage.
DANGER
Do not exceed the test voltages given in Table 3 . Exceed-
ing 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 switchgear,
proper isolation of the power-frequency source from the
VLF test source must be maintained . Follow the recom-
mendations provided by the manufacturer of the VLF test
equipment . Follow the user’s operating and safety proce-
dures 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, dis-
charging the cable, and regrounding the cable .
WARNING
When VLF cable testing has been completed or has been
interrupted, you must discharge the cable system and the
test equipment . Allow the time needed to fully discharge
the cable system and test equipment . Failure to fully dis-
charge the cable system and test equipment can result in
serious damage to the cable system and test equipment .
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.
