Abstract:With the application of power cable and the development of distribution system, the capacitance current at fault location will increase when single phase grounding fault occurs. The capacitance current may lead to further development of the fault and can be extinguished by using grounding-type arc-extinguishing device. In neutral point ungrounded distribution system that equipped with grounding-type arc-extinguishing device, the action of grounding-type arc-extinguishing device will change the present status of distribution system and may lead to saturation of the iron core of potential transformer (PT) and cause PT ferroresonance. The principle of the appearance of PT ferroresonance is studied by analyzing the influence on the distribution system caused by the action of grounding-type arc-extinguishing device and considering both the excitation characteristics of PT iron core and the characteristics of ferroresonance circuit. An iterative computing method base on the excitation characteristics of iron core and the characteristics of ferroresonance circuit that can represent the non-linear process of resonance is proposed. The theoretical analysis method and iterative computing method are proved effective by experiments on MATLAB.