Research on Arc Grounding Fault Detection of 10 kV Three-Core Cable Based on Magnetic Field Inversion

With the cabling reconstruction of urban medium voltage distribution network, three-core cables are gradually used to replace overhead lines. Theoretically due to the zero-sequence current of three-core cable is zero in steady state, the traditional ferromagnetic current transformer cannot be applied to the non-intrusive arc grounding fault detection of three-core cable. Therefore, this paper proposes a method to measure the zero-sequence current of 10 kV three-core cable by using magnetic sensor array. First of all, the three-core cable model is established. On the basis of Maxwell equations and finite element method (FEM), the relationship between the magnetic field distribution and each phase current can be obtained. Secondly, Considering the randomness and eccentricity of the installation position of the magnetic sensor array, a circular sensor array with six equidistant measuring points is ultimately designed. Then, combined with the Ampere circuital theorem, the nonlinear equations of each phase current and the tangential magnetic field intensity at measured points are constructed. Besides, the tangential magnetic field distribution around the cable is compared under non-magnetic armor and magnetic armor, which indicates that the nonlinear equations are still applicable under magnetic armor cable. Using EMTP software to simulate the arc grounding fault, it can be seen that after the arc grounding fault occurs, the current values change abruptly. Thus, by extracting the tangential magnetic field intensity at measured point, the inversion solution of fault current waveform can be used to detect the occurrence of arc grounding fault. Finally, the feasibility of the method is verified by power current experiment. The experimental results show that the current amplitude error is less than 1 %.