1. Measure insulation resistance

It should be carried out on each phase separately, the other two-phase conductors, the metal shield or metal sheath and the armor layer at both ends of the cable are connected, for this test. Just notice that the cable is a capacitive device, and you should pay attention to the insulation resistance and absorption ratio of the capacitive device. For example: full discharge before and after the test, fire first and then overlap, disconnect first and then power off and shake the meter.

2. DC withstand voltage and leakage current test

Oil-paper insulated cables only do DC withstand voltage, not AC withstand voltage, because the increase in AC Ig may cause thermal breakdown. In the hot state, the electric field is unevenly distributed and the cable is easily damaged. It should be noted that the cable core wire is connected to the negative polarity: when the cable is damp, the water will have a positive charge. If the core is connected to the negative polarity, moisture will be concentrated on the core wire, the moisture in the insulation will increase, the leakage current will increase, and defects will be easily found. If the core wire has a positive polarity, moisture will penetrate into the lead package, and the moisture in the insulation will decrease, and the leakage current will decrease, making it difficult to find defects.