Research About The Transient Current Protection Relay For HV/EHV Transmission Line

The reliability of HV/EHV transmission line protection is important to the security of the power system. This thesis is devoted in the study of the transient current protection for HV/EHV transmission line. The thesis mainly concerns the following aspects:to apply wavelet transform and statistics analyse theory in fault transient signal processing ,to study of transient current protection principle,criterion and behavior.The auther studies the analyse and processing of fault transient signal. The thesis introduces the definition of transient current and it's energy.The tranvelling wave can be affected by power system equipment,it's effect is analysed with energy change of transient current at high frequency band. The Mallat decomposition properties of wavelet transform(WT) is introduced. The application of WT to power system fault signal is also discussed in the thesis. The auther also studies the application of statistics analyse theory.Spectral analysis and system identify method can be used to analyse noise energy distribution and damp characteristics of bus capacitance. The author studies the prolems of principle and criterion of transient protection based on fault current,and gives a new scheme of tranisent protection. The recursive criterion of transient current protection based on Mallat wavelet transform is presented in order to meet the real-time demands.The reserch shows deficiency existed in the prevenient principle of transient current protection,so a new improved scheme of transient current protection is proposed.The characteristics of transient protection at different bus distribution capacitance is also analysed in this thesis.The study shows that operate of transient protection is correct when the bus distribution capacitance change.Other conclusion include: the trip of transient protection must be locked when the power circuit breaker of transimission line operated,because the trip is incorrect at this time;the features of transient current and it's energy is different between the fault and thunder over- voltage in transimission line,and them can be identified;the ratio of high frequency component of current in serise capaciters compensation line , SVC and HVDC system is far little than fault transient current, so all of them do not affect the working of trasient current protection.