39
High-potential tests
The next series of tests (vacuum-integrity
test and insulation tests) involve use of
high-voltage test equipment. The circuit
breaker under test should be inside a
suitable test barrier equipped with warning
lights.
Vacuum-integrity check (using dielectric
test)
A high-potential test is used to verify the
vacuum integrity of the circuit breaker. The
test is conducted on the circuit breaker with
its primary contacts in the Open position.
Vacuum integrity test procedure
1. Observe safety precautions listed in the
danger and warning advisories.
Construct the proper barrier and
warning light system.
2. Ground the frame of the circuit breaker,
and ground each pole not under test.
3. Apply test voltage (refer to Table 4)
across each pole for one minute (circuit
breaker Open).
4. If the pole sustains the test voltage for
that period, its vacuum integrity has
been verified.
Note: Do not use dc high-potential testers
incorporating half-wave rectification. These
devices produce high peak voltages.
High peak voltages will produce X-ray
radiation. DC testers producing excessive
peak voltages also show erroneous readings
of leakage current when testing vacuum
circuit breakers.
Vacuum interrupters may emit X-ray radiation.
Can result in serious injury.
Keep personnel more than six feet away from a circuit breaker under test.
Equipment
maximum voltage
rating kV
Equipment rated
power-frequency
withstand kV (rms)
Maximum ac rms
test voltage kV
Maximum dc
average test voltage
4.76 19 14 20
8.25 36 27 38
15.0 36 27 38
15.5 50 38 53
27.6 60 45 64
38 80 60 85
Table 4: High-potential test voltages
High-potential test voltages
The voltages for high-potential tests are
shown in Table 4.
Note: This test includes not only the
vacuum interrupter, but also the other
insulation components in parallel with the
vacuum interrupter. These include the post
insulators and the insulating coupler, as well
as the insulating (tension) struts between
the upper and lower vacuum interrupter
supports. If these insulation components are
contaminated or defective, the test voltage
will not be sustained. If so, clean replace the
affected components, and retest.
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