Insulating oil is a commonly used insulation, arc extinguishing and cooling medium for electrical equipment. In order to ensure that it has good performance during operation, it must be tested regularly, especially the pressure test. The withstand voltage test of the insulating oil is carried out in a special breakdown voltage tester. The tester includes a porcelain or glass oil cup and two 25 mm diameter disc electrodes (should be smooth and free of burn marks). During the test, pour the oil sample taken out into the oil cup, and then put it into the electrode so that the two electrodes are 2.5 mm apart. The test should be carried out in a room with a temperature of 10 to 35°C and a relative humidity of not more than 75%.
The specific test steps are as follows:
(1) Mix the oil sample evenly, as far as possible not to make it generate bubbles. Put it indoors for a few hours to make the oil temperature as close to room temperature as possible.
(2) Connect the oil sample to the test circuit and let it stand for 10-15 minutes to allow the bubbles in the oil to escape.
(3) Turn on the power supply and pressurize at a speed of 3 kV per second. When the oil sample is broken down (significant spark discharge or trip switch of the tester), record the instantaneous voltage value.
(4) After standing for 5 minutes, repeat the above test. Generally, each oil sample needs to be tested 5 times, and the average voltage value of 5 times is taken.
(5) If necessary, another two oil samples can be taken for the same test, and the average voltage value of the three oil samples can be taken as the test result.
(6) If the voltage is added to the maximum value of the tester (such as 50 kV), the oil sample has not broken down, and it can stay at the maximum voltage for 1 minute without breaking down, the insulating oil is considered qualified.