40
High-potential test voltages
The voltages for high-potential tests are
shown in Table 2 (or 3): High-potential test
voltages on page 23 (or 33).
Note:
The dc test voltage is given as a
reference only. It represents values believed
to be appropriate and approximately
equivalent to the corresponding power-
frequency withstand test values specified for
each voltage rating. The presence of this
column in no way implies any requirement for
a dc withstand test on ac equipment or that a
dc withstand test represents an acceptable
alternative to ac withstand tests. When
making dc tests, the voltage should be raised
to the test value in discrete steps and held for
a period of one minute.
Note: Do not use dc high-potential testers
incorporating half-wave rectification. Such
devices produce high-peak voltages.
These high voltages will produce X-ray
radiation. Such devices also show erroneous
readings of leakage current when testing
vacuum circuit breakers.
Vacuum integrity test procedure
1. Observe safety precautions listed in the
danger and caution advisories. Construct
the proper barrier and warning light
system.
2. Ground each pole not under test.
3. Apply test voltage across each pole for
one minute.
4. If the pole sustains the test voltage for
that period, the vacuum integrity has
been verified.
Note:
This test includes not only the vacuum
interrupter, but also the other insulation
components in parallel with the vacuum
interrupter. These include the standoff
insulators and the insulated drive links, as
well as the insulating (tension) struts
between the vacuum interrupter (polehead)
supports. If these insulation components are
contaminated or defective, the test voltage
will not be sustained. If so, clean or replace
the affected components, and retest.
If dc high-potential tests are used, note the
following:
If a dc test indicates loss of vacuum,
reverse the polarity of the test leads and
retest.
If the second test is successful, the
vacuum interrupter has adequate vacuum
integrity.
If the second test also indicates loss of
vacuum integrity, replace the vacuum
interrupter.
As-found insulation and contact-
resistance tests
As-found tests verify the integrity of the
circuit breaker insulation system. Megger* or
insulation-resistance tests conducted on
equipment prior to installation provide a basis
of future comparison to detect changes in the
protection afforded by the insulation system.
A permanent record of periodic as-found tests
enables the maintenance organization to
determine when corrective actions are
required by watching for significant
deterioration in insulation resistance, or
increase in contact resistance.
Insulation and contact-resistance test
equipment
In addition to the high-potential test
equipment capable of test voltages as listed
in Table 2 (or 3): High-potential test voltages
on page 23 (or 33), the following equipment
is also required:
AC high-potential tester with test voltage
of 1,125 volts, 60 Hz.
Micro-ohmmeter for contact-resistance
tests.
*Megger is a registered
trademark of Megger
Group, Ltd.
Summary of Contents for SDV7-AR
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