Breakdown strength test:
1. The power cable oil into oil cup has standard electrodes (electrode is 25 mm in diameter, spacing of 2.5 mm, axis alignment of these two electrodes, and maintain a level, oil standard capacity of not less than 250Cm3, an electrode from the oil level of oil painted and not less than 15 mm).
2. From scratch processing frequency ac voltage, breakdown, read the breakdown voltage. Then, with a clean glass rod dial several times in the electrode (do not change the gap distance), in order to get rid of the breakdown of the free carbon, rest 5 min before the next test (from scratch), repeat 5 times, and take its breakdown voltage as a sample of the average breakdown strength. If any one of the five measurements value and the difference between the average is more than plus or minus 25%, should be tested again. When necessary, desirable test three cups, breakdown test per cup five times, and then take the average. Cable oil breakdown voltage should be at room temperature greater than a 45 kV gap (2.5 mm).