| In medium voltage network, it often happens ferroresonance which caused by nonlinear characteristic of excitation inductance in potential transformer, it will cause overvoltage and overcurrent, seriously, will cause fuse fusing even potential transformer burned or explosion, and this phenomenon will impact the secure operation of power system.In this paper, the reason of ferroresonance occurring and the common suppression measures are described. In medium voltage network, when phase to ground voltage appears asymmetry and some phase voltage rises, the iron core of PT becomes saturated, its excitation inductance decreases, when to match the capacitance of the system, ferroresonance occurs. Along with the increase of capacitance of the system, stimulated resonance will be high-frequency, fundamental or fractional frequency. The common suppression measures mainly include:improving excitation characteristic of PT, increasing capacitance to ground of the network, connecting a damping resistance to the broken delta winding, connecting a linear or nonlinear resistance or single-phase PT to the neutral point of three-phase PT’s primary winding, connecting an arc-extinguishing winding or resistance to the neutral point of power system, and so on. It established the simulation model based on ATP-EMTP program in the paper. With single phase grounding fault disappearing as stimulating conditions, it simulates exciting ferroresonance when capacitance to ground and inductance parameters matching, and simulation analysis various suppression measures, compares the effects of eliminating ferroresonance. Finally, a new eliminating measure is put forward—resonance eliminator with modified PT, and the simulation shows its validity. The new measure overcomes the voltage measurement error problem by resonance eliminator method, it also avoids the problem the4PT method will not eliminate ferroresonance quickly in big capacitance current system. |
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