S&C Instruction Sheet 695-505 27
Appendix A
WARNING
The VLF ac withstand capacity of the switchgear may
be reduced because of aging, damage, or electrical or
mechanical wear. Therefore, the ac test voltage must
be selected so 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.
WARNING
Do not exceed the test voltages given in Table 5.
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
switchgear, 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 operating 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.
Failure to follow
these recommendations can result in a flashover,
injury, and equipment damage.
NOTICE
When VLF cable testing has been completed,
or has been interrupted, the cable system and the
test equipment must be discharged. 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.
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. Since 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 inter-
rupters is not recommended. For those users who desire
to test the vacuum interrupters, contact the nearest S&C
Sales Office for specific instructions.
Table 5. Vista SD Switchgear Very Low Frequency (.01- to 1-Hz) Sinusoidal Waveform Maximum Test Voltages
Vista SD Switch-gear
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
