Research On Adaptive Reclosure Method Of Transmission Line Based On Improved Variational Mode Decomposition

Ultra High Voltage(UHV)transmission lines have the characteristics of long transmission distance and large capacity,but they are exposed all year round and prone to failure due to uncertain factors such as the external environment.Therefore,how to remove the fault and ensure its safe and stable operation is of great significance.Compared with automatic reclosing with fixed time limit,adaptive reclosing has the function of distinguishing fault type and arc extinguishing time,which can effectively prevent the reclosing from causing secondary shock to power system and equipment in permanent fault or incomplete arc extinguishing stage.Based on the different characteristics of the voltage of different fault phase,this paper presents a method to determine the fault type and the arc extinguishing time.Firstly,this paper describes the background and current situation of single-phase adaptive reclosing research,and studies the arc characteristics and fault phase voltage characteristics of UHV transmission lines with shunt capacitors at both ends of the circuit breaker based on shunt reactor eliminating the small neutral grounding reactance.Secondly,the influence of the voltage shunt capacitors on the transient process of the fault is analyzed in detail,the voltage difference of the fault phase in different fault types is studied,and an adaptive rectification scheme based on the improved Variational Mode Decomposition(VMD)and Energy Entropy(EE)is proposed.The improved VMD method was used to decompose the voltage signal of the fault phase and obtain the IMF component with characteristic quantity signal.Then,the energy entropy of each IMF component was calculated to obtain the energy entropy of the original signal.The faulty type was determined by setting a reasonable threshold based on the difference of energy entropy under different fault properties.Through Empirical Mode Decomposition(EMD)of the same fault signal characteristics analysis,this paper has verified the effectiveness of VMD algorithm.A large number of EMTP simulation results show that this method is not affected by fault location,transition resistance,shunt compensation degree and other factors.It can improves the reclosing success rate.Finally,the spectrum characteristics and energy entropy curve flatness of voltage signals before and after single-phase grounding failure of UHV transmission lines with and without shunt reactors are analyzed in detail.This paper presents a method for determining arc extinguishing of secondary arc based on improved VMD energy entropy curve flatness.The terminal voltage signal of secondary arc contains a large number of high frequency harmonics before extinguished.Its components are complex,and its energy entropy value is large,and the entropy curve is sharp pulse output,which is not flat.However,after the arc is extinguished,the original energy storage of the circuit is rapidly released and the signal is stable.The energy entropy value of the circuit is small and rapidly decays to zero,and the entropy curve is relatively flat.A large number of simulation results show that the method is less affected by fault location,power Angle difference,transition resistance,parallel compensation,etc.The error is small and it can judge the time of arc extinguishing effectively.