Abstract
Long distance three-phase power cable has the characteristics of the metal sheath cross-bonded and voltage drop and ground potential difference at both ends, which brings confusion to on-line insulation monitoring of long distance power cable. One parameter monitoring cable insulation will effect by voltage drop, load current change, frequency fluctuation and other factor. A method based on dielectric loss factor and resistive current to monitor cable insulation simultaneously has been put forward. The method named as a multi-parameter on-line cable insulation monitoring method. The method installs current transformers and voltage transformers on both side of three-phase cable and uses a high precision timing function of the GPS receiving module at both ends of the testing equipment respectively which can receives the pulse per second from the GPS satellite as time reference can realize the signal synchronous sampling. The principle and formula of the method are given. The metal sheath cross-bonded equivalent circuit of long distance three-phase cable is established by using MATLAB software and does dynamic simulation on the method. The results show that the method is not effect on load current, voltage drop and frequency fluctuation. The two parameters increase obviously when the cable operating temperature exceeds 80°C. The insulation condition of three-phase cable can be judged by the change of dielectric loss factor and resistive current under different insulation fault. The method was proved to be correctness and feasibility in the paper.
Highlights
The cross-linked polyethylene (XLPE) cable is widely used in the field of power transmission lines and ultra-high voltage transmission, because of its excellent insulation and mechanical and thermal properties [1, 2]
It can be seen from that the on-line insulation monitoring of cable with a single parameter may be affected by many factors, such as frequency fluctuation, voltage drop, temperature, harmonic, ground potential difference, phase change during measurement and so on [10,11,12,13]
The frequency fluctuation of the power grid leads to barrier effect and frequency leakage caused by asynchronous sampling, which causes errors in monitoring results of cable insulation [17]
Summary
The cross-linked polyethylene (XLPE) cable is widely used in the field of power transmission lines and ultra-high voltage transmission, because of its excellent insulation and mechanical and thermal properties [1, 2]. The basic problems of on-line monitoring insulation for long distance power cables are as following: First, the metal sheath of three-phase cables is cross connection. It can be seen from that the on-line insulation monitoring of cable with a single parameter may be affected by many factors, such as frequency fluctuation, voltage drop, temperature, harmonic, ground potential difference, phase change during measurement and so on [10,11,12,13]. Those factors make the monitoring parameter accurately. The principle and formula of the multi-parameter method are given and the comparative simulation study proves the feasibility and effectiveness under different conditions
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