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MAINTENANCE Page 21
VACUUM CHECK
A sufficient level of vacuum is necessary for
proper performance of the vacuum interrupters.
Although vacuum leaks are rare, the vacuum
integrity should be checked periodically. The
relationship between dielectric breakdown
voltage of the contact gap and internal vacuum
interrupter pressure has been found to be
generally predictable. Therefore, vacuum
interrupter integrity is checked by performing a
high potential test across the open gap of the
interrupter.
TEST EQUIPMENT:
Toshiba offers a compact vacuum checker (Type
CI35-1D, Figure 11) which enables a quick and
easy check on vacuum interrupter internal
pressure. Alternatively, any commercially
available AC high potential tester may be used
which is capable of delivering at least 25 milli-
amperes at 10 kV for a period of one minute.
PRECAUTIONS:
Applying abnormally high voltage across a pair
of contacts in vacuum may produce X-rays. The
radiation may increase with the increase in
voltage and/or decrease in contact spacing. X-
radiation produced during this test with
recommended voltage and normal contact
spacing is extremely low and well below the
maximum permitted by standards. As an
additional safety measure, however, it is
recommended that all personnel keep at least 1
meter (3.3 ft) away from the vacuum circuit
breaker while this test is performed.
Radiation exposure hazard.
X-rays may cause illness or
injury. Stay at least 1 meter
(3.3 ft) away from the circuit
breaker during the vacuum
check test.
Hazardous voltages are
present during dielectric
testing which can result in
severe injury or death.
Only qualified personnel
should conduct this testing.
TEST PROCEDURE:
1. The contactor should be disconnected from
the main circuit and be in the OFF position.
2. Connect all the line side primary terminals
together and to the output of the vacuum
checker or AC hi-pot machine. Connect all
the load side primary terminals together and
to the ground terminal of the vacuum
checker or AC hi-pot machine.
3. Increase the voltage from zero to 10kV AC at
a rate of approximately 1kV per second.
Hold the voltage at this value for 1 minute
and observe the current drawn by the
interrupter. See Figure 12.
4. Decrease the voltage back to zero.
Figure 11 - Toshiba Portable Vacuum
Checker
WARNING
WARNING
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