A Novel Neutral Electromagnetic Hybrid Flexible Grounding Method in Distribution Networks

This paper proposes a flexible neutral grounding method based on electromagnetic hybrid Petersen coil (EHPC), which consists of a magnetically controlled reactor and an active power compensator (APC). Under normal conditions, the system's neutral point grounds through a reactor of high reactance. When a single line-to-earth fault occurs, the EHPC can be controlled flexibly to suppress the recovery voltage of faulty phase and to reduce the ground-fault current to almost zero. This paper expounds the two operating modes and corresponding characteristics, the measuring method of insulation parameters of the system (mainly including capacitance to earth and leakage resistance), and the full compensation principle for arc suppression based on the equivalent negative impedance of EHPC. This paper also proposes a compound control method of neutral-to-earth impedance based on neutral-point displacement voltage and a compensating method for the harmonic component of the ground-fault current. Compared to traditional grounding methods, this method can be fast and reliably make the residual current approach almost zero without arc reignition while greatly reducing the output capacity of APC and, thus, decreasing the cost of this device. Simulations and experiments verify the correctness of this measuring method and feasibility of this flexible grounding control strategy.