The service life and operation safety of cross-linked cables are affected by the cable quality, installation and construction technology and operation environment.
The only detection means of cable quality and installation and construction technology is the cable handover test, and the detection of the cable under the influence of the operating environment after the operation needs to rely on regular preventive tests.
The accident of cable equipment can be prevented to the greatest extent through the handover test and preventive test of the crosslinked cable.
The test items of handover test and preventive test are basically the same.
But because the purpose of the two experiments is different, so the focus of the experiment is different.
According to relevant regulations, the crosslinked polyethylene insulated power cable needs to do insulation resistance measurement, DC withstand test and leakage current measurement, AC withstand test, measurement of metal shield layer resistance and conductor resistance ratio, inspection of the two ends of the cable line phase, cross interconnection system test 6 items.
Notes for handover test
Cable handover test shall be carried out after cable laying and cable accessories installation, but not before cable lapping and electrification.
The handover test is mainly aimed at the transportation, laying and installation of cable accessories after leaving the factory.
The following questions should be paid attention to during the test:
The handover test is generally for newly installed cables.
As the withstand voltage test is a kind of destructive test, in practical operation, it is generally chosen to choose one between dc withstand voltage test and AC withstand voltage test.
The damage to the insulation layer of the cable by DC withstand voltage test is cumulative. Every time the DC withstand voltage test is done more, the insulation performance of the cable will decline a little.
The working conditions of AC withstand voltage test are relatively harsh, and many cables tested are outdoors. For bulky AC withstand voltage equipment and huge AC test power supply, it requires several hours of fully enclosed test environment requirements.
The phase inspection at both ends of cable line should be emphasized in handover test.
This kind of inspection is relatively simple, as long as the multimeter is used to check the phase of the tested cable one by one, so as to avoid the problem of cable phase mislabeling or leakage labeling. If the phase of both ends of the cable is mislabeled, it means that some three-phase electrical reverse phase accidents may occur.
During inspection, connect a core wire to the ground wire of the cable in turn at one end, and measure the on and off of the ground wire of the cable with a multimeter or resistance meter at the other end. Measure 3 times per core for a total of 9 times. After the test, the phase marks at both ends should be consistent.
Precautions for preventive tests
The preventive test is a kind of testing of the cable according to a certain period after the cable is put into operation.
Prior to the test, the original test data of the tested cable should be obtained to facilitate the evaluation of the operating environment and condition of the tested cable during the test.
After the sample (s) made by the original test data, when the main cable insulation resistance value of the insulation, the insulation resistance of cable outer sheath, cable lining layer insulation resistance values, copper shield resistance and the ratio of conductor resistance values, and comparing the test data transfer and data and little change in the acceptable range, you should not make direct current withstand voltage test.
Dc voltage withstand test should be carried out on the cable only after it is judged that the outer sheath and lining layer of the cable is damaged and filled in water, the newly made terminal head and intermediate joint, and the copper shielding layer of the cable is treated.
To test the insulation resistance of the outer sheath of the cable, measure the resistance of the steel armor to the ground insulation, and mainly check whether the outer sheath of the buried cable is damaged.
As new cables generally have no water into the cable, the insulation resistance of the outer sheath is generally better, and the use of several years of the old cable is different, some of the cable soaked in water if there is a little damage, it is likely to water.
When the insulation resistance per kilometer is lower than 0.5 megom, water or moisture may appear in the outer sheath of the cable, which will have a very significant impact on the service life of the cable.