38
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.
High-potential test voltages
The voltages for high-potential tests are
shown in Table 5.
Equipment
maximum voltage
rating kV
Equipment rated
power-frequency
withstand kV (rms)
Maximum ac
rms test voltage kV
Maximum dc
test voltage kV
15.5
50
38
53
27.6
60
45
64
38
80
60
85
Table 5: High-potential test voltages
Figure 20: Manual check of vacuum integrity
48.0
Item
Description
48.0
Insulating coupler (shown disconnected on right pole for checking
vacuum integrity)
48.6
Lever
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 (16.1) and the insulating coupler,
as well as the insulating (tension) struts
(28.0) 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.
As-found insulation and contact
resistance tests
As-found tests verify the integrity of the
circuit breaker insulation system. Megger*
or insulation-resistance tests and contact-
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, and in the integrity of the current
carrying path. 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 increases in contact
resistance.
* Megger is a registered trademark of
Megger Group, Ltd.
Insulation and contact-resistance test
equipment
In addition to the high-potential test
equipment capable of test voltages as listed
in Table 5, the following equipment is also
required:
AC high-potential tester with test voltage
of 1,500 volts, 60 Hz
Test equipment for contact-resistance
tests.
Insulation and contact-resistance test
procedure
1. Observe safety precaution listed in the
danger and warning advisories for the
vacuum integrity check tests (refer to
pages 37).
2. Ground the frame of the circuit breaker.
Apply control power for electrical
charging of capacitors (106.2). Close the
circuit breaker.
3. Apply the proper ac or dc high-potential
test voltage (refer to Table 5: High-
potential test voltages on page 38)
between a primary conductor of the
pole and ground for one minute.
