The wiring method of the test transformer during DC withstand voltage or leakage tests

The wiring diagram for the test transformer when conducting the DC withstand voltage or leakage test on the tested item is shown in Figure 7.
Note: This test should be carried out first by removing the short-circuit lever “D”, as shown in Figure 7.

In the figure: VD – high-silicon diode stack R1 – current-limiting resistor C1 – high-voltage filter capacitor
RCF – Capacitive Voltage Divider CX – Test Sample uA – With Protective Microampere
In the leakage test, the limiting resistor R1 is selected such that the short-circuit current at the output terminal does not exceed the larger rectification current of the high-voltage silicon diode when the rated output voltage is applied. For example, if the larger rectification current of the voltage silicon diode is 100mA and is used in a 60KV test device, the limiting resistor should be selected as R = 60 / 0.1 = 600KΩ. The limiting resistor should also have sufficient capacity and the gap for surface discharge. The high-voltage filter capacitor C1 is generally selected in the range of 0.01 – 0.1uF. When the capacitance of the tested item is very large, C1 can be omitted.

 Procedure and precautions for the leak test:

1) Before conducting the test, it is necessary to first check whether the test subject has been powered off, whether the static electricity has been discharged, and whether all external connections have been wiped clean. Special precautions must be taken to prevent the test voltage from being applied to any area where people are working.
2) After connecting the wiring of the test device, it should be rechecked to ensure there are no errors before applying pressure. Special attention should be paid to checking the safety distance between the high-voltage equipment and the ground, as well as between the equipment and the operators. The grounding of the test specimen’s casing should also be verified. The test should be conducted in accordance with the requirements specified in the safety regulations.
3) For equipment with large capacitance, the voltage should be increased slowly to prevent the charging current of the tested item from damaging the microammeter. If necessary, the voltage should be increased in stages, and the stable readings of the microammeter at each voltage level should be recorded separately.
During the test process, the test subject, the test equipment, and the microammeter should be closely monitored. In case of any abnormal phenomena such as breakdown or flickering, the voltage should be immediately reduced, the power supply should be cut off, and the cause should be identified. Detailed records should be made.
5) After the test is completed, reduce the voltage, cut off the power supply, and then fully discharge the test subject and the test equipment itself.