S&C Vista Series - Dielectric Testing; Routine Switchgear Testing; Cable Testing and Fault Locating

S&C Instruction Sheet 681-510 25
Dielectric Testing
Routine Switchgear Testing
For the convenience of users who normally perform
electrical tests on system compo nents such as switchgear,
appropriate with stand test values for Vista switchgear are
given in Table 1. These test values are signicantly greater
than the normal operating voltage of the switchgear and
are near the ashover voltage of the gear. They should
be applied only when the switchgear is com pletely
de-energized and disconnected from all power sources.
WARNING
When performing electrical withstand tests on Vista
switchgear, al ways observe the following precautions.
Failure to observe these precautions can result in a
flashover, injury, and equip ment 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.
3. Verify that the SF
6
-gas pressure gauge is in the
Green zone.
Table 1. Maximum Insulation Test Voltages
Vista Switchgear Rating, kV Withstand Test Voltage, kV
50 Hertz 60 Hertz Impulse (BIL)
Power
Frequency
①
Dc②③
12 15.5 95 27 42
24 27 125 40 62
36 38 150 50 82
① The listed power-frequency withstand test voltages are approxi-
mately 80% of the design values for new equipment.
② The listed dc withstand test voltages are approximately 80% of the
design values for new equipment.
③ Dc withstand test voltages are given for reference only for those
users performing dc withstand tests. The presence of these values
does not imply a dc withstand rating or performance requirements for
the switch gear. A dc withstand design test is specified for new equip-
ment because the switchgear may be subjected to dc test voltage when
connected to the cable. The listed dc withstand test values are approxi-
mately equal to the ac peak test voltage.
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-Volt age Tests on Power Cable Systems in the
Field,” describe such testing and should be referenced for
selection of the test proce dures. Dc testing also includes
cable “thump ing,” i.e., the sudden application of dc voltage
from a large capacitor for the purposes of fault locating,
which causes transients and voltage doubling at the end of
the open cable. When the cables are attached to the switch-
gear, the gear will also be subjected to the dc test voltages.
WARNING
The dc withstand capability of the switchgear may be
reduced because of aging, damage, gas leakage, or
electrical or mechanical wear. Therefore, the dc test
voltage must be selected so it does not exceed the
withstand limits of the switchgear. Application of dc
test voltages greater than the withstand capability
of the switchgear can result in a flashover, injury,
and equipment damage.
In addition, always verify that the SF6-gas pressure
gauge is in the Green zone before proceeding with
any testing.
DANGER
Do not exceed the test voltages given in Table 2 on
page 26. 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 of the dc
test source and result in severe personal injury
or death.