Maintenance
High-potential test voltages
The voltages for high-potential tests are
shown in Table 2: High-potential test
voltages on page 23.
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: High-potential test
voltages on page 23, 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.
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