The Research On Ferroresonance Overvoltage In Ultrahigh Voltage Converter Station

The UHV operation and maintenance experience in recent years has shown that in the converter station in the core area of UHV DC transmission,due to the charging and connecting process in the station or the opening and closing of the circuit breaker and other operations,the station system will be disturbed,resulting in iron core inductance.The equipment changes from the normal state to the saturated state.When the inductance parameters of the equipment and the capacitance parameters of the station system meet the matching conditions,the ferromagnetic resonance will be excited.The generation of the ferromagnetic resonance overvoltage may cause the electrical equipment in the converter station to overheat or even burn out.The mechanism of the transient process is complex,causing a series of safety hazards to the safe and stable operation of UHV DC transmission projects.Therefore,it is necessary to carry out ferromagnetic resonance simulation and theoretical research on the ferromagnetic resonance in the relevant converter station,and analyze the effectiveness,feasibility and economy of various suppression measures on the basis of the existing resonance elimination measures,and obtain the corresponding faults.The best choice for the UHV converter station provides a theoretical basis and reference basis for the implementation of harmonic elimination in the UHV converter station.This article first analyzes and discusses the mechanism of ferromagnetic resonance,theoretically derives the occurrence of ferromagnetic resonance,describes the characteristics and hazards of ferromagnetic resonance,and expounds the H.A.Peterson test results and the division of ferromagnetic resonance parameters.The second is to establish an electromagnetic simulation model using PSCAD based on the fault case of the ferromagnetic resonance of the voltage collector of the transformer bushing terminal screen of the UHV converter station,analyze and explain the cause and process of the fault,and analyze the nonlinearity of the ferromagnetic resonance from the perspective of mathematical theory.Theoretical research,the use of De Moffer’s theorem and small interference method to analyze the input and output characteristics of nonlinear links and the essential reasons for the stable existence of non-power frequency resonance,and lay a theoretical foundation for the proposal of harmonic elimination measures.The third is to investigate and analyze the different standby states of circuit breakers,the installation of damping resistors at the variable neutral point,the station variable rated capacity,and the main CVT through PSCAD transient simulation software for ultra-high voltage converter station transformer ferromagnetic resonance faults.The influence of factors such as capacitance on ferromagnetic resonance.Finally,based on the ferromagnetic resonance phenomenon that occurred in the two converter stations,a variety of resonance elimination measures were proposed and through simulation analysis,the best choice of resonance elimination measures was found from the aspects of feasibility and economy.The research results in this paper show that: for the ferromagnetic resonance of the bushing end screen of the converter valve side in the UHV converter station is excited by the AC-DC coupling disturbance in the charging-to-connection process,it is proposed to change the loop LC parameters and the voltage collector once Two types of harmonic elimination measures are increased by increasing the damping resistance on the side.In terms of complexity and economy,it is believed that although the principle of changing the LC parameters is clear and the theoretical basis is strong,it needs to involve the rectification of the secondary side relay protection device,which is heavy and cumbersome;the method of increasing the damping resistance to consume resonance energy The operation is simple,only involves the modification of one circuit element,and the impact on the voltage measurement accuracy is also very weak,which can be used as the best choice.Aiming at the ferromagnetic resonance case of 500 k V station transformer in ultra-high voltage converter station,convert the hot standby state of circuit breaker B5022 to cold standby state,reduce the circuit breaker voltage equalizing capacitance,put damping load on the 10 k V side,and change the primary side of the station transformer.Measures such as winding connection methods and improving station-use variable excitation characteristics will inhibit ferromagnetic resonance.From the perspective of practicality and feasibility,replacing a circuit breaker with a smaller voltage equalizing capacitor can suppress the occurrence of resonance and is preventive.Strong,can be used as the best choice.