The ultra-low frequency withstand voltage test is characterized by no damage to the tested cable, and it can also test the cable that is aging but can still be used. Therefore, it is a non-destructive withstand voltage test method.This test is more accurate than the DC high voltage test in judging the wrong connection between the newly laid cable and the repaired cable.
"Ultra low frequency (0.1Hz) withstand voltage test method for 35kV and below XLPE insulated power cables" industry standard. According to the requirements of this industry standard, the test procedures are as follows:
All electrical equipment connected to the test object shall be separated from the test object cable, and the test equipment (ultra-low frequency high voltage generator, etc.) shall be reliably grounded with bare copper wire.
Conduct insulation resistance test on each phase of the tested cable with 10000v megger, and record the test value.
Peak value of test voltage: 2UE, test time: 60min.
When the capacitance value of the test cable is within the load capacitance capacity of the test equipment, the three-phase cores of the test cable can be connected in parallel and the withstand voltage test can be carried out at the same time.
Connect the test equipment with the cable of the test object with a flexible connecting cable, turn on the power supply and start boosting for the test. In the process of boosting, closely monitor the high-voltage circuit and monitor whether there is abnormal noise in the cable of the test object. When the test voltage rises, record the test time and read the test voltage value.
When the test time is up, first reduce the voltage to zero, and then cut off the power supply. If there is no destructive discharge during the test, it is considered to have passed the withstand voltage test.
In the process of boosting and withstand voltage, if it is found that the pointer of the voltmeter swings greatly, the indication of the ammeter increases sharply, the voltage regulator continues to boost, but the voltage remains basically unchanged or even shows a downward trend, while the current increases greatly, and the test cable emits peculiar smell, smoke or abnormal sound or flashing, the boosting shall be stopped immediately, and the cause shall be found out after the step-down power failure. If these phenomena are found to be caused by the weak insulation part of the cable under test, the withstand voltage test is considered to be unqualified. If it is determined that the test cable is caused by air humidity or surface dirt, the test cable shall be cleaned and dried before the test.
During the test, if the test is interrupted due to the accidental loss of power supply due to the insulation defect of non test cable, the full-time connection withstand voltage test shall be carried out again after finding out the cause and restoring the power supply. The "make up time" test alone shall not be performed.
