With As the electric cable is extensively used, two topics are raised: ① how to locate the fault quickly and correctly after the cable is out of order; ② how to carry out effective tests for cables on a regular basis ?
Several Cable Test Methods
The cable test mainly focuses on insulation layer and the leakage, dielectric, loss and partial discharge characteristics of cable insulation should be taken into account.
M meter has many kinds of different voltage stages, including 500kV, 1000kV, 2500kV, 5000kV and 10kV. The M meter is used to measure the resistance of insulation, which reflects the leakage characteristic of cable insulation.
The DC dielectric test reflects the leakage and dielectric characteristics of cable insulation. Both theoretical analysis and practical effect show that the DC or AC dielectric characteristic of oil-filled cable, gas-filled cable or oil-immersed paper cable is basically the same. Because the solid dielectric cable such as rubber and plastic cable (including XLPE cable) has sphere gap in the insulation layer, the sphere gap will discharge at DC condition, thus enhancing the dielectric strength. Meanwhile, the back-EMF cannot disappear in time so accumulative effect forms. When changing applied-voltage direction, dielectric strength reduces significantly. Therefore, DC dielectric test cannot fully reflect the actual withstand situation of cable, but sometimes do damage to the cables.
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