Some domestic research institutes believe that in the DC withstand voltage test of XLPE cable, the actual electric field strength in the insulation can be up to 11 times higher than that of the cable insulation due to the space charge effect. The XLPE insulated cable will cause serious damage to the insulation even if it does not break through the DC withstand voltage test. Second, the applied DC voltage field strength distribution is different from the operating AC voltage field strength distribution. The DC withstand voltage test can not truly simulate the overvoltage of the cable under running conditions, and effectively find the defects of the cable and cable joint itself and the construction process. Therefore, the use of non-DC methods for the pressure test of cross-linked cables has received more and more attention. At present, ultra-low frequency power supplies have been used in the medium and low voltage cables for pressure test. However, due to the low voltage level of such VLF, it cannot be used for high voltage cable tests of 110kV and above. In China, this method has also been used for low-voltage cables, but due to the test equipment, it has not been widely promoted. In recent years, due to the construction of urban and rural power grids, cross-linked cables have been used more and more. The cables are put into operation only after the DC withstand voltage test, and the cable or cable head breakdown occurs under the operating voltage. Cases also occur from time to time. Therefore, everyone is exploring new test methods.
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Cable withstand test device
In recent years, research results of many international and domestic research institutions have shown that the DC withstand voltage test of power cables has different degrees of damage to XLPE cables. Some researches believe that the XLPE cable structure has the ability to store and accumulate unipolar residual charge. If the DC residual charge cannot be effectively released after the DC withstand voltage test, the DC residual charge plus AC after operation. Voltage spikes can cause breakdown of the cable.