Study on on-line insulation monitoring for 500kV submarine cable

Taking insulation condition of the submarine oil-filled cable which used in Hainan Interconnection Project as the research object, a new method of on-line monitoring has been put forward in the paper. To monitor the current of each phase cable which flowing through the grounding line and cable core by installing current sensors on the grounding line and cable itself respectively. The ratio of leakage current and the inductance of grounding circuit current can be calculated which can be used to judge the sheath insulation has no leak point. The on-line monitoring system basic on the new method has been introduced, including the system composition, the function of each part. The results showed that the monitoring system which can real reaction condition of the cable insulation. The system has successfully been put into operation in Hainan Interconnection project at present, the operation condition is good and test data is reliable, provided an important basis on monitoring submarine oil-filled cable insulation. The monitoring method also can be applied on on-line monitoring of other long distance cables insulation.