S&C Vista SD - Maintenance; Inspecting Cable Terminations

S&C Instruction Sheet 695-545 21
Appendix A
Routine Switchgear Testing
For the convenience of users who normally perform
electrical tests on system components such as switchgear,
appropriate withstand test values for Vista SD Underground
Distribution Switchgear are given in Table 1 as well as
Table 2 on page 22. These test values are signicantly
greater than the normal operating voltage of the switchgear
and are near the ashover voltage of the switchgear. They
should be applied only when the switchgear is completely
de-energized and disconnected from all power sources.
WARNING
When performing electrical withstand tests on Vista SD
Underground Distribution Switchgear, always observe
the following precautions. Failure to observe these
precautions can result in a flashover, injury, and
equipment damage.
1. Completely de-energize the switchgear and
disconnect it from all power sources.
2. Terminate the bushings with an insulated cap or
other appropriate cable termination capable of
withstanding the test voltage.
Table 1. Maximum Insulation Test Voltages
Vista SD Switchgear Rating, kV
Withstand Test Voltage,
kV
IEC IEEE
Impulse
(BIL)
Power
Frequency
①
Dc
②③
12 17.5 95 31 42
24 29 125 45 62
①The power-frequency withstand test voltages listed in the table are approximately
80% of the design values for new equipment.
②The dc withstand test voltages listed in the table are approximately 80% of the
design values for new equipment.
③Dc withstand test voltages are given for reference for those users performing dc
withstand tests. The presence of these values does not imply a dc withstand rating
or performance requirements for the switchgear. A dc withstand design test is speci-
fied for new equipment because the switchgear may be subjected to dc test voltage
when connected to the cable. The dc withstand test voltages listed in the table are
approximately equal to the ac test voltage.
Dc Cable Testing and Fault Locating
Dc testing of installed cables is performed to determine
the condition of the cables and to locate faults. Industry
standards such as IEEE 400, “IEEE Guide for Making
High-Direct-Voltage Tests on Power Cable Systems in the
Field,” describe such testing and should be referenced for
selection of the test procedures. Dc testing also includes
cable “thumping” (the sudden application of dc voltage
from a large capacitor for the purpose of fault locating),
which causes transients and voltage doubling at the end
of the open cable. When the cables are attached to the
switchgear, the unit will also be subjected to the dc test
voltages.
WARNING
Aging, damage, or electrical or mechanical wear may
reduce the dc withstand capability of the switchgear.
Therefore, the dc test voltage must be selected such
that it does not exceed the withstand limits of the
switchgear. Application of dc 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 1.
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 of the dc test source and result in
severe personal injury of death.