Research on High voltage Cable Insulation on-line Monitoring Technology Based on Double differential CT Method

Aiming at the problem that the leakage current signal obtained in XLPE cable insulation state diagnosis is easy to be interfered, this paper proposes an on-line monitoring technology of high voltage cable insulation based on the principle of double differential CT with compensation. The principle of double differential CT is to install current transformer (CT) at the headend and end of each phase cable. The A, B and C three-phase current transformers at the headend and the end of the cable line are connected in series, and the zero sequence current at the headend and end is obtained by current difference. And then the zero sequence current of the insulation leakage current of the three-phase cable is obtained by the difference between the zero sequence current of the headend and the end. At the same time, the phase information of zero sequence current of the leakage current of cable insulation is identified by taking the differential current at the headend and end of any phase cable as reference. After that the insulation state of the fault cable can be distinguished. Based on the theoretical analysis, the simulation model of double differential CT is built. The simulation results show that there is a positive correlation between the output value of the secondary differential and the specific determination of the aging state of the phase insulation. That is, the deeper the aging degree is, the larger the output value of the secondary differential is, which verifies the correctness of the proposed dual differential CT method with compensation.