Research On Fault Current Characteristics Of Doubly-fed Wind Turbine And Its Effect On Line Relay Protection

Doubly-fed induction generators(DFIG)are very sensitive to the disturbances of grid,so dynamic characteristics of its rotor current become very important under the rapid increase of DFIG-based wind generation.The implementations of low voltage ride through and short-circuit calculation of electric quantities depend on the accurate assessment of rotor current,And it is not ignored that the influence of transient electric capacity of wind power system on relay protection.In this paper,doubly-fed wind power generator based on the Crowbar protection fault characteristic research,without ignoring the condition coupling of the stator,rotor resistance and flux.It is given that the analytic expression on flux and current,and simulation verification is proposed.The short-circuit current includes the frequency periodic component of the non-full phase voltage,the fast attenuation speed of the frequency offset and the dc attenuation component.The relation is studied between amplitude and attenuation factor of stator transient magnetic and the influence factors,such as speed,Crowbar resistance and so on.Crowbar resistance significantly contributed to the attenuation effect of transient decay component,application of Prony analysis on actual short-circuit current harmonic component are analyzed,and indirectly verified the short circuit current and attenuation characteristics of each component.It is found that the resistance of low wear hardware has a great influence on the positive sequence impedance of DFIG.With the increase of Crowbar resistance,the negative resistance of positive sequence impedance increases and the positive resistance increases to saturation.The increase of positive sequence impedance strengthens the weak feed of the wind farm to the system under short circuit fault.As fault point location away from the wind farm side or transition resistance increases gradually,to the wind farm to the system of weak feed has superposition effect when three phase short circuit occurs,severe extreme voltage drop,the vast majority of short-circuit current is dc component and the rotating frequency component,power frequency components are very few,short circuit current under the action of unloading resistance decay quickly,so that the measurement impedance calculation formula of the denominator rapidly decreases,and distance protection calculation accuracy affected by severe;The existence of the transition resistance amplifies the protection range accuracy error,affect the distance is a movement of timeliness,instantaneous measurement using the impedance circuit fixed action characteristic of impedance relay,at the same time can effectively reduce the influence of wind power weak feed and transition resistance.