Research On The Influence Of Double-fed Fan Access On Line Relay Protection And Protection Strategy

With the increasing application of wind power generation in electrical power system,it have caused a lot of problems,thus bringing many negative factors on relay protection.The current mainstream wind-driven generator is doubly fed induction generator(DFIG).Considering the unique synchronization method and exciting mode of DFIG,it is very necessary to allow for the impact of DFIG on the relay protection of integrated circuit and collector line and outgoing line of wind power plant and study the measures to improve the reliability of outgoing line protection of wind power plant.This paper firstly introduces the principle and mathematical model of DFIG.Based on these,the paper derives the analytical formula of current of DFIG stator and rotor in case of Crowbar protection operation.Then,it analyzes the impact of the characteristics of short-circuit current on traditional distance protection.Under symmetric fault and asymmetric fault,measured data are used to analyze the operating characteristics of traditional distance protection of integrated circuit of doubly-fed wind power plant,and simulation data are used to analyze the operating characteristics of directional pilot protection with distance relay of outgoing line of doubly-fed wind power plant.And analysis of the influence of short circuit current characteristics of doubly fed induction generator on traditional distance protection.Considering that the frequency deviation characteristics of short-circuit current of doubly-fed wind power plant may cause inaccurate operation of traditional collector line and outgoing line protection,this paper researches the principle of time domain protective scheme.It is applicable to doubly fed wind power plant.In this scheme,power transmission line is equivalent to R-L line model.According to the instantaneous value of measured voltage and current,recursive least square method is employed to identify the parameters of unknown quantities and the measured impedance is obtained.According to the relationship between measured impedance and setting impedance,the fault area can be identified.Besides,time domain quantity is used to build directional pilot protection of outgoing line.This scheme takes section II of distance protection at both ends of line as the direction identification element,and identifies the fault direction based on the operating criteria for time-domain distance directional element,so as to achieve directional pilot protection of time domain distance.In addition,it conducts simulation analysis of protective measures for outgoing line of wind power plant based on the time-domain protection scheme under symmetric fault and asymmetric fault.The simulation results show that,this scheme is independent from the impact of frequency deviation characteristics of short-circuit current in the wind power plant.Meanwhile,it can identify the fault direction accurately and quickly and a capability to resist transition resistance,and improves the operation reliability of collector line and outgoing line protection of doubly-fed wind power plant.In view of the impact of transition resistance on the outgoing line of doubly-fed wind power plant,this paper researches a quadrilateral characteristic-like distance protection scheme.This scheme takes into consideration the impact of transition resistance and then redesigns the operating area of distance protection.Through simulation analysis of the operating performance of circular characteristic distance protection,the results show that this scheme has a strong ability to resist transition resistance.However,this scheme may be affected by the parameters of transmission line and it is unable to detect the location accurately.Based on the above analysis,this paper studies a new protection method that combines distance protection with differential protection.In this scheme,the active power at both ends of the transmission line is used to calculate the transition resistance.Finally,removes the error impedance caused by transition resistance from measured impedance,its effective impedance of the transmission line is obtained.The results indicate that the distance-differential protection method is not affected easily by transition resistance,and it is able to detect the fault location accurately and improve the operation reliability of outgoing line protection of doubly-fed wind power plant.