Toshiba HV6AS instruction manual Vacuum Check, Maintenance, Page

MAINTENANCE Page 29

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

WARNING

Hazardous voltages are present during dielectric testing which can result in severe injury or death. Only qualified personnel should conduct this testing.

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) 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 22 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.

TEST PROCEDURE:

1.The circuit breaker 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 22kV AC at a rate of approximately 2kV per second. Hold the voltage at this value for 1 minute and observe the current drawn by the interrupter.

4.Decrease the voltage back to zero.

Fig. 34 Toshiba Portable Vacuum Checker

WARNING

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 .