Research On Phase Selection Method Of Open-phase Fault Condition

At present,the phase selection methods commonly used in power system such as the method based on symmetrical component and the method based on superimposed component,are aimed at a single fault,and have good phase selection performance under single fault condition.When the power system is under open-phase fault condition,the characteristics of electricity will change.The original phase-selection methods may take the wrong phase.Therefore,the main work of this paper is to establish a phase selection method suitable for open-phase fault condition.Based on the basic theories of fault analysis and relay protection,this paper analyzes all kinds of open-phase faults.According to the superposition theorem,the system under open-phase condition can be divided into the superposition of the additional state of short circuit and the open-phase state.Calculating the additional state of short circuit which is equivalent to the representation of self-impedance and mutual impedance by the loop current method,and get current fault component increment,which is not influenced by the load current and current fault components.In this paper,the mechanism analysis and formula analysis methods are applied to extract the amplitude characteristic of current fault component increment under various additional state of short circuit of open-phase fault condition.Besides,a new fault phase selection scheme is propose in this study by characterizing the magnitude of current fault component increment and introducing the voltage amplitude characteristic and the existence of zero-negative sequence current as auxiliary criteria,which can achieve the correct trip under open-phase fault condition and put into the impedance component which has most obvious fault characteristics.Finally,through the analysis of influencing factors,the phase selection scheme proposed in this paper is less affected by the transition resistance and not affected by the impedance angle differences and overload factors of the system.The conclusion shows that the phase selection method proposed in this paper can realize fast and reliable phase identification when the system is under open-phase fault condition,which can effectively improve the reliability of phase selector.