(1) Clean and dry the oil testing cup, standard gauge, glass rod for mixing and glass plate as the plate cover.
(2) After the temperature of the test oil is close to the room temperature, slowly invert the test oil bottle twice to make it mix evenly (without bubbles).
(3) Flush the oil cup and gauge with oil test for three times. Adjust the electrode spacing, and use a special gauge to measure that the spacing is exactly 2.5mm, and then slowly flow the test oil down the glass rod for mixing until the oil level is no less than 15mm above the point. Then cover the glass cover and let it stand for 15min to overflow the bubbles in the oil.
(4) The AC power supply with the frequency of 50Hz shall be used and connected in parallel, and the voltage shall be boosted at the speed of 3kV/s uniformly, which shall not be too fast, otherwise the voltage rise will be uneven. Raise the pressure until the oil test in the cup breaks down. At this time, after the switch automatically trips, the pressure reducing handle can be returned, the power supply can be cut off, and the highest voltage value reached by the voltage breakdown is recorded, that is, the breakdown voltage.
(5) Use a glass rod with a diameter of 2mm to remove carbon particles caused by breakdown between electrodes. Do not produce foam during mixing, and do not touch oil with hands. After mixing, stand still for 5min.
(6) Measure 6 times continuously according to the above steps to obtain 6 breakdown voltages in total, and take the arithmetic mean value as the breakdown voltage value of the oil test, namely, the dielectric strength E=U/d (U is the average breakdown voltage of the oil test, kV; d is the electrode gap, mm).
Pay attention to the following points in the test: (1) The distance between electrodes 2.5 ± 0.1mm shall be calibrated with a special gauge; (2) The average value of 6 times shall be taken as the test result according to the test method; (3) To ensure the representativeness of the sample, the sample shall be shaken well before being injected into the oil cup. When injecting the test oil, the test oil shall flow down the inner wall of the cup to reduce bubbles; (4) Do not touch the electrode, the inside of the oil cup and the oil test with your fingers during operation.
