Research On Insulation Method Of Submarine Cable

The submarine cable used in Hainan interconnection project, which has a span of 31.8km, adopts self-contained high-voltage oil-filled cable with no cable joint during connection and two-terminal-grounding. To guarantee the safe and stable operation of the submarine cable, it is necessary to monitor the insulation condition. However, few researches are developed on this aspect in the whole world. Therefore, a useful monitoring method based on the particularity of the submarine cable in Hainan interconnection project is introduced in this paper.Compared with land cable, the submarine cable has its unique structure and operation mode. Moreover, the surroundings where it is situated are more complex. After study on all kinds of monitoring methods of cable, it is found that conventional monitoring methods have some disadvantages which are not suitable for the submarine cable. In order to monitor the insulation condition of submarine cable, researches on the monitoring method of oil-paper and shield insulation are developed respectively in this paper according to the operation condition, grounding mode and structure parameters of the submarine cable. And finally, the grounding currents in the shield and lower frequency voltage and current signals are chosen to reflect the status of the shield insulation and the oil-paper insulation respectively.The further research shows that that the grounding currents in the cable shield contain two different currents, the inductive current and the capacitive current. Due to the submarine cable's special grounding mode, the inductive current, which depends on the load current in cable transmission, will not be influenced after the change of the insulation condition outside the shield. However, the capacitive current, which depends on the operation voltage and the insulation condition, can not only detect the fault of the shield insulation, but also can locate the failure cable. The oil-paper insulation is much more reliable in comparison with the shield insulation. If the oil-paper insulation has been detected declining, it can be restored by change the insulation oil. Due to the submarine cable without any intermediate joint, this paper only considers monitoring the whole insulation by measure the tanδvalue. The results show that it can effectively avoid all kinds of problems under the operation frequency by using low-frequency signal to detect the value of tanδ, which proposes a new idea for the implementation of the on-line monitoring of the cable insulation.