Research On Ferroresonance Overvoltage Of Non-ground Neutral System

The electromagnetic potential transformer (PT) is used to detect bus voltage in non-ground neutral system, it often causes ferroresonance overvoltage by the nonlinear excitation characteristics of PT, when the system is disturbed, and the phenomenon will impact safe and stable operation of the power system.This paper analyses the mechanism of ferroresonance by basic ferroresonance circuit, displacement of the frequency overvoltage, harmonic overvoltage caused by saturated PT, ferromagnetic parameter range, researches the different ways of ferroresonance excitation with the disappearance of single-phase ground fault, arc grounding fault and open-phase running system, summarizes the characteristics and damages of ferromagnetic.This paper builds a simulation model by MATLAB/SIMULINK based on the actual operation parameters of35kV non-ground neutral system of an urban rail transit, researches ferromagnetic overvoltage due to the different ways of excitation; it studies the influence on the ferromagnetic caused by system operation mode, initial phase angle of ground fault disappear time, system capacitance, three phase capacitance unbalance, PT primary side direct current resistance and grounding resistance based on the disappearance of single-phase ground fault mode. The simulation result shows that ferromagnetic overvoltage is closely related to the initial phase angle of ground fault disappear time, and also be constrainted by system capacitance, PT primary side direct current resistance, grounding resistance and so on.According to the simulation model, this paper compares the effect of use the PT which have better excitation characteristic, use CVT to replace PT, increase system capacitance,4PT grounding method, syetem neutral point grounded with resistance, grounded with arc suppression coil, PT primary side neutral grounded with resistance and PT open delta series resistance to suppress the ferromagnetic. The simulation result shows that the measures used to suppress ferroresonance have good effects, but all of them have defects and applicatable scope.This paper proposes to use adjustable impedance transformer as new arc suppression coil to suppress ferroresonance, due to the defects of commonly used measures, and verifies it’s effectiveness through the simulation.