General regulations for preventive tests of power cable lines
When measuring the insulation resistance or conducting withstand voltage tests on the main insulation of the cable, it should be done separately on each phase; when measuring or testing one phase, the conductors, metal sheaths, metal jackets and armor layers of the other phases should be directly grounded together. When conducting withstand voltage tests on the main insulation of a single-core cable with a metal sheath or metal jacket that has a sheath overvoltage protector at one end and is short-circuited at the other end, the sheath overvoltage protector should be short-circuited to ensure that the metal sheath or metal jacket of the cable at that end is grounded.
For cable lines with a rated voltage of 0.6/1kV, the insulation resistance between the conductors and the ground can be measured using a 1000V or 2500V megohmmeter instead of conducting a withstand voltage test.
When conducting a DC withstand voltage test on oil-paper insulated cables, the voltage should be increased uniformly in stages (at least 3 stages), with each stage lasting for 1 minute, and the leakage current should be recorded. During the process of the test voltage rising to the specified value and the test duration reaching the specified time, the leakage current should be read at least once. The leakage current value and the imbalance coefficient (the ratio of the larger value to the smaller value) can be used as references for judging the insulation condition. If the leakage current changes significantly compared to the previous test value, or if the leakage current is unstable and rises sharply with the increase of test voltage or the extension of test duration, the cause should be investigated.
If the leakage current on the surface of the terminal head or the stray current to ground is the cause of the problem, it should be eliminated. If there is suspicion that the insulation of the cable line is poor, the test voltage can be increased (not exceeding the factory test voltage specified in the product standard) or the test time can be extended to determine whether the equipment can continue to operate.
After the pressure test, when discharging to the conductor, it is necessary to repeatedly discharge through a limiting resistor of approximately 80 kΩ per kilovolt several times until there is no spark, and then direct grounding discharge is allowed.
Except for self-contained oil-filled cable lines, for other cable lines, before they are put into operation after being de-energized, it is necessary to confirm that the condition of the cable lines is in good condition. The following tests can be carried out respectively to determine this:
a) If the power outage lasts for more than one week but less than one month, measure the main insulation’s insulation resistance (handle any abnormalities as per d).
b) If the power outage lasts for more than one month but less than one year, measure the insulation resistance of the main insulation. It is advisable to conduct a main insulation withstand voltage test, with the test duration set at 5 minutes (handle any abnormalities as per d).
c) If the power outage lasts for more than one year, a main insulation withstand voltage test should be conducted. (In case of any abnormalities, handle it as per d.)
d) During power outages, if there is suspicion of external force damage to the lines, or if abnormalities are detected during the pre-operation inspection, preventive tests should be conducted.
Post time: Jul-21-2026