Research On Adaptive Distance Protection Of Distribution Network Connected To Photovoltaic Power

With the implementation of policies such as photovoltaic poverty alleviation,more and more miniature solar power plants have been formed,making the penetration rate of distributed power sources continuously increasing.The flexible access location,high penetration rate and transition resistance of the distributed generation have caused the problems of traditional distance protection rejection action and wrong action.Therefore,in order to ensure the safe and stable operation of the power grid in the new mode,this paper proposes an improved adaptive distance protection method,and simulation to verify the effectiveness of the method.The following work was carried out:First,according to the modeling guidelines of photovoltaic power generation system and new grid connection requirements,this paper considers the control strategy of normal operation and fault operation,and establishes a DG equivalent model.The simulation analysis shows that the equivalent of the distributed generation as a current source controlled by the positive sequence voltage at the grid connection point can accurately characterize the fault current of the DG.Second,this paper analyzes the impact of DG's different access methods on the three-section distance protection.Through analysis,the distributed generation causes protection rejection action and erroneous action mainly because the transition resistance generates additional impedance.The additional impedance makes the measured impedance not reflect the positive sequence impedance from the protection point to the fault point.The setting impedance is not a fixed value because of the distributed generation.Third,this paper adopts an adaptive distance protection method to adaptively adjust the measured impedance and the set impedance.For the additional impedance generated by the transition resistance,the fault impedance is calculated by passing the triangular relationship between the fault impedance,the measured impedance,and the additional impedance.The fault impedance can reflect the line impedance between the measurement point and the fault point,so it has higher resistance to transition resistance.In view of the influence of DG on the setting impedance,this method introduces the self-adaptive amount of setting impedance generated by DG to modify the setting impedance.This method does not require communication support.Fourth,by comparing with the traditional distance protection,the fault impedance obtained by using?_z compensation can reduce the resistance component or inductive reactance component of the measured impedance,and improve the resistance to transient resistance.The self-adaptation of the set impedance to the set impedance can make the protection that fails to operate normally due to the influence of the distributed generation operate correctly.This paper has 56 figures,19 tables and 77 references.