“Power cable operation regulation” stipulates that under the condition of not losing normal oil pressure, it is not necessary to conduct DC withstand voltage test regularly for high voltage oil filled AAAC Cable. As long as the oil pressure is normal and the dielectric loss and breakdown strength of oil are qualified, it can be considered that the cable insulation is reliable. Therefore, oil filled cable should be tested regularly to measure its dielectric loss and breakdown strength. The test period is generally sampled one year after putting into operation. If the results of two consecutive tests do not change, the test period can be gradually extended. In addition to the oil sample test, the following tests should also be carried out.
1. Measure the insulation resistance of outer sheath
the outer sheath of oil filled cable not only insulates the metal sheath from the ground, but also has anti-corrosion effect on the lead sheath and reinforcing tape. The insulation resistance of the sheath of oil filled cable shall be measured once a year by insulation resistance meter or other methods to check the integrity of the sheath insulation and the degree of water seepage. The high pressure oil filled cable is under the positive oil pressure, and the moisture in the air cannot invade people. Periodic measurement of outer sheath insulation can find out the early mild damage of sheath. When measuring the insulation of protective layer, the transposition bar and protector on transposition board in cross interconnection box shall be disassembled, and the insulation resistance of protective layer shall be measured by sections. Long lines shall be measured with electric insulation resistance meter.
2. Measure the grounding resistance
in the sheath grounding system with two ends grounded, one end grounded or cross interconnection connection, the value of grounding resistance will affect the operation of the protector. GEOX type grounding resistance measuring instrument can be used to measure the grounding resistance of the cable sheath connected with the grounding electrode or the grounding connecting line of the protector.
3. Measure the DC resistance of conductor
by measuring the DC resistance of the conductor and comparing it with the test values in previous years, we can check the change of the contact resistance between the outgoing stem or connecting pipe and the cable core, and judge whether the conductor connection is good.