Wuhan UHV specializes in producingseries resonance (also known as AC withstand voltage test equipment). Next, we will share with you the overcurrent protection setting values for AC withstand voltage test.

The voltage, waveform, frequency, and distribution of the internal voltage of the tested insulation in the AC withstand voltage test all conform to the actual situation when operating under AC voltage, and can truly and effectively detect insulation defects. It is one of the methods to test the insulation withstand overvoltage ability of the tested insulation and has important significance for ensuring the safe operation of equipment.

In the process of AC withstand voltage of electrical equipment, in order to ensure that the test power can be quickly and reliably cut off in case of short circuit and breakdown of the test object during the test, we must set the overcurrent protection setting in advance.

According to engineering experience, the overcurrent protection setting is generally set to about 1.3 times the rated test current of the untested sample.  

The test current is calculated based on the voltage applied during the test and the capacitance of the test object. The calculation formula is as follows:

Ic=0CxUt 

Ic test current (mA) 0 test power supply angular frequency

Cx test sample capacitance (uF) Ut test voltage (kV)

Excerpt from GB50150 regarding cable testing

18.0.1 Rubber insulated power cables with DC withstand voltage have obvious disadvantages: the electric field distribution under DC voltage is different from that under AC voltage, and cannot reflect the actual operating conditions. The report of the CIGRESC21WG21-09 working group of the 21st Research Committee of the International Conference on Power Grids and the proposal document for the new work project of IECSC20A do not recommend using DC withstand voltage test as the completion test for rubber insulated power cables. This has also been proven by operational experience. Some cables successfully passed the DC withstand voltage test during the handover test, but insulation breakdown accidents occurred shortly after being put into operation; It is not uncommon for cables in normal operation to be damaged by DC withstand voltage tests. Therefore, in this article, it is required to conduct AC withstand voltage tests on rubber insulated power cables. It should be emphasized that the AC withstand voltage of 20~300Hz still includes the power frequency (50Hz) test. But for rubber cables with a voltage of 18kV and below, the latest version of IEC60502-2:2005 has given priority to AC withstand voltage, but still temporarily retains DC withstand voltage, with a special note added: "DC withstand voltage may be harmful to insulation; other test methods are still under consideration." Therefore, in this article, it is required that DC withstand voltage test be allowed for rubber cables with a voltage of 18kV and below only when the conditions are not met.