Study On Internal Fault Characteristics And Magnetizing Inrush Current Of Four-winding Inductively Filtered Power Transformer

Nowadays,the vigorous development of power electronic devices has made the power quality in power systems face a severe test.The harmonic problems generated further threaten the safe and economic operation of power transmission lines,power equipment,relay protection and other communication facilities in power systems.The Four-winding inductively filtered power transformer studied in this paper is suitable for multi-port substation with harmonic source inflow.It can realize local suppression of harmonic components and compensation of reactive power,the harmonics on the load side is prevented from entering the grid side essentially.In this paper,the Four-winding inductively filtered power transformer is taken as the research object,and its working mechanism,mathematical model,internal fault characteristics and magnetizing inrush current identification are discussed,which lays a foundation for further protection research of such new transformers.Firstly,starting from the coupling circuit of Four-winding inductively filtered power transformer,this paper deduces the two impedance conditions that it must have to meet the requirements of induction filter,and further expounds the essential reasons of reducing harmonic component and restraining its internal flow in transformer from the perspective of magnetic flux;according to the necessary impedance conditions,the winding arrangement scheme and parameter design of Four-winding inductively filtered power transformer is deduced.Based on this,a prototype machine that meets the requirements of induction filtering is developed.Secondly,based on the concept of mutual coupling between windings,this paper establishes the mutual coupling model of Four-winding inductively filtered power transformer under normal operation state and internal fault state,and establishes the mutual coupling simulation model of Four-winding inductively filtered power transformer considering core saturation module in MATLAB.In order to solve the problem that it is difficult to determine the leakage factor in the mutual coupling internal fault model,the field-circuit coupling model under two different states is established by using Ansoft Maxwell software.Thirdly,on the basis of the field-circuit coupling model of the internal faults of Four-winding inductively filtered power transformer,the simulation analysis of turn-to-ground faults and inter-turn faults under three different operating conditions is carried out,which shows that the internal faults of network-side windings will affect the steady operation of transformer.By changing the number of faults and the fault location,the fault severity in different situations is compared and the corresponding conclusions are drawn.Finally,the generation principle and various influencing factors of the magnetizing inrush current are analyzed and expounded.Based on the mutual coupling model of the Four-winding inductively filtered power transformer considering the core saturation,the waveform characteristics of the magnetizing inrush current are obtained through simulation analysis.By using the method of wavelet transform,the distinction between inrush current and internal fault current of Four-winding inductively filtered power transformer is realized,and an effective identification method is proposed.