Study On Distance Protection Based On Novel Phase Selection Methods For Transmission Line Of DFIG-based Wind Farm

Nowadays,the traditional non-renewable resources are facing the crisis of use,and countries are actively developing new energy power generation.When a large-capacity wind farm is connected to the system,it will show the characteristics of weak infeed and uncertainty,which is quite different from the traditional power plants,and will affect the relay protection of the wind farm transmission line to a certain extent.This paper mainly studies the principle of phase selection of distance protection on wind farm transmission line,and proposes a novel superimposed phase selection method to adapt to the characteristics of wind farms.This paper are analyzes the fault current characteristics and transient equivalent impedance characteristics of doubly-fed introduction generator(DFIG).It shows that the amplitude and phase angle of the positive and negative sequence transient equivalent impedances of DFIG have changed greatly under two low voltage ride through modes of converter control and crowbar protection,which has strong weak feed characteristics.The principle of the superimposed current phase selector is analyzed,and it is found that the weak feed and sequence impedance difference of wind farm lead to the decrease of the superimposed current.In this paper,the amplitude of the ratio of one phase fault component and the other two phases’ phase difference fault component is used as a factor,and then the adaptive coefficient is introduced through the impedance information of the power sources on both sides.The voltage factor and current factor are combined as the phase selection coefficient to form a new phase selection principle,so as to improve the deficiency of the superimposed current phase selector on the weak feed side,and improve the sensitivity and reliability of phase selection.Phase difference of sequence impedance of wind farm and weak infeed of wind farm amplify the influence of transition resistance.On the basis of the phase angle difference of the positive and negative sequence superimposed current,the virtual amplitude composed of the amplitude of the ratio of the minimum value of the phase-to-phase current fault component and the maximum value of the single-phase current fault component is introduced.Then repartition the phase region on the complex plane.The scheme avoids the phase error caused by transition resistance when two-phase grounding fault occurs.The power frequency variation distance protection is greatly affected by the equivalent impedance phase angle of wind farm.In this paper,the vector replacement method is proposed to improve the operation sensitivity after determining the phase angle of fault voltage and current.The distance protection based on the self-adaptive synthesis superimposed phase selection and virtual amplitude division phase selection can better adapt to the weak infeed and uncertainty of the wind farm,solve the possible protection rejection caused by false phase selection,and improve the safety of distance protection.MATLAB/Simulink simulation platform is used to build a grid model with a doubly-fed wind farm.Considering the relative capacity changes on the wind farm side and the system side,as well as the different fault types,fault locations and transition resistances,the new phase selection principle of the distance protection of the transmission line is simulated and verified.The simulation results verify the rationality of the proposed phase selection scheme and the reliability and sensitivity of the distance protection action based on the new phase selector,and ensure the safety of the distance protection work.