Test of leakage current of switching appliances

The leakage current test of switching equipment can effectively detect insulation moisture and local defects of insulation (can sensitively reflect porcelain cracks, internal moisture and local looseness of interlayer insulation, cracking of insulating oil, carbonization along the surface of insulation, etc.). It is closely related to the insulation resistance test. The difference is:

(1) The DC power supply used in the leakage current test is generally supplied by high-voltage rectifier equipment, and the voltage is high and can be adjusted arbitrarily.

(2) For samples with different voltage levels, corresponding test voltages can be applied to check for defects.

(3) During the test, follow the instructions of the microammeter to keep track of the insulation condition. The wiring principle is shown in the figure below.

For the wiring in Figure (a) below, the microammeter is on the low-voltage side, which is more convenient for reading, but it cannot eliminate the error caused by the leakage current on the insulation surface and the corona current of the high-voltage lead; Figure (b) the microammeter on the high-voltage side On the other hand, although the above errors can be eliminated, reading and shifting are very inconvenient. The test steps are as follows:

① After fully discharging the crystal under test, connect the wiring as shown below, and set the indicating instrument to zero and the voltage regulator to zero.

② Turn on the power switch, pressurize the boost circuit, and then adjust the voltage regulator to gradually boost the voltage to the predetermined test voltage value; read the leakage current value according to the residence time required by the test product.

③After the test is completed, return the voltage regulator to zero position and cut off the power supply.

④After each test, the tested product must be discharged to the ground through a resistor first, and then directly to the ground; during discharge, the insulation condition can be roughly understood based on the size of the discharge spark.