On-line monitoring method for long distance power cable insulation

There are cross-linked metal sheath and voltage drop in the long distance power cable which make difference between the short and the long distance power cables on on-line insulation monitoring technology. In order to solve the problem, two terminal synchronous tanδ measurement as a new method of on-line insulation monitoring had been put forward in the paper. The working principle and theoretical basis of calculation were given. The feasibility of the method was demonstrated when there was synchronization error in the system. The Matlab software was used to simulate the circuit of three-phase cable and to calculate tanδ of cable insulation. The results show that the load current will not influence on tanδ measurement if choose the average of vector sum of voltage at the two ends of the cable. And the harmonic and frequency fluctuation had little influence on the methods. The methods were proved to be validity and feasibility in the paper. It can be obtained that the methods were suitable for all kinds of cable insulation monitoring whether the metal sheath of three-phase cable was cross-linked or not.