Research On Line Unit Pilot Protection Scheme In Abnormal Synchronization Scenarios

With the development of smart substations,the communication system has realized the networking of the secondary side of the power system,and the synchronization of sampled data is increasingly dependent on the communication network.However,there are various abnormal operating conditions of the communication system,such as abnormal network timing,optical fiber communication delays,etc.,resulting in abnormal data synchronization.In abnormal synchronization scenarios,the performances of various protections will deteriorate sharply,and even lead to protection refusal or mal-operation,which seriously threatens the safety of the power system.In order to deal with the impact of abnormal synchronization,the power system has adopted a variety of data synchronization methods.However,regardless of the point-to-point mode or the networking mode,traditional data synchronization methods cannot guarantee complete elimination of synchronization errors.In terms of protection configuration,high-voltage transmission lines generally adopt the redundant configuration of dual main protection,in which current differential protection requires strict synchronization of data on both sides of the line.Once the data synchronization is abnormal,the relay protection device will block the differential protection until synchronization is restored,and the protection performance will be greatly affected.The action of the unit protection depends on the comparison of the electrical quantities at each end of the protected area.Because its operating characteristics are only related to the transmission line and the electric quantity sensors,the unit protection has absolute selectivity and high reliability.Therefore,the paper takes the unit protection as the starting point and combines data synchronization methods to propose a unit protection scheme with synchronization error tolerance capability.Aiming at the impact of abnormal synchronization on the unit protection,the paper analyzes the action behavior of line unit protections.In abnormal synchronization scenarios,the current differential protection will appear protection refusal or mal-operation,and the probability is directly related to the ratio braking coefficient.Based on the active power differential protection,the paper proposes the fault component instantaneous power to ensure the rapidity,and analyzes the characteristics of its phase trajectory.The active power differential protection has stronger capability to tolerate synchronization errors,but there is still the possibility of mal-operation.On this basis,the paper proposes to use the fault component instantaneous active power as the characteristic quantity to conduct researchIn order to improve the reliability of the active power differential protection,the paper analyzes the transient process of the fault component instantaneous active power in detail.Combining the fault data self-synchronization method,the paper proposes the power differential protection scheme,which can cope with the complete loss of synchronization on both sides of the line.It has been verified by PSCAD that the proposed protection scheme has an average action time of 3.69ms in synchronous scenarios,and can operate correctly in abnormal synchronization scenarios,and has the advantage of fast actionIn order to fully simulate the impact of abnormal synchronization in engineering,the paper develops a protection prototype based on the ZYNQ platform,builds a closed-loop test system based on the RTDS platform,and performs verification.Based on the overall functional framework of the ZYNQ platform,the paper designs the software and hardware to realize the protection and communication functions.An IEEE 9 model and digital communication interface models are built,and a closed-loop test system for synchronous scenarios is established.Using the COMTRADE PLAYBACK model to construct synchronization errors,a closed-loop test system for abnormal synchronization scenarios is established.The paper verifies the synchronization error tolerance capability and corresponding performances of the proposed protection scheme.Experimental tests show that in synchronous scenarios,the average protection action time is 5.29ms;in abnormal synchronization scenarios,the proposed protection scheme can correctly distinguish the fault location,and the protection action time is linearly related to the synchronization error.