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 10) 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 milliamperes 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 contactor 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
contactor 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 (Figure 11).
4.
Decrease the voltage back to zero.
Figure 10 - Toshiba Portable Vacuum
Checker
WARNING
WARNING
