Testing Methods for Power Cable Insulation

Testing methods for power cable insulation depend basically on type and material of cable insulation. Cross-linked Polyethylene (XLPE) is now spreading widely for power cable insulation at the rated voltage of 66 to 154 kV world-wide, and especially in Japan many 275 kV lines have already been put in service. Typical conventional power cable insulation is oil-impregnated paper which is used mainly for oil-filled cable above 66 kV in many countries, including Japan. Testing methods for both of these types of power cables in Japan are introduced here in comparison with those prevailing in the USA together with the reason for each testing method or condition. In general, there is no fundamental difference between testing methods in Japan and in the USA. However, test voltages are decided by the insulation thickness and the specified stress in the USA, while test voltages in Japan are given directly by the rated voltage. Tests described here cover factory tests to be made at the time of delivery, acceptance tests after installation at site, and maintenance tests to be made during operation.