| Gas insulated switchgear(GIS)has the advantages of saving space,safe and reliable operation,small maintenance,long overhaul period,etc.It is widely used in the transmission network of 110KV and above,especially in the EHV/UHV transmission network.The operation of disconnector switches,circuit breakers and grounding switches in GIS,and the ground faults of GIS internal conductors can all produce very fast transient(VFT)phenomena.Among various kinds of VFT phenomena,the damage caused by very fast transient overvoltage(VFTO)is the most serious and most concern.VFTO affects the safe operation of winding equipment,secondary equipment and GIS ontologies,and especially poses a great threat to the insulation safety of transformers and other winding equipment.VFTO has caused several accidents on site.For example,faults caused by VFTO occurred in China Guangdong Nuclear Power,Zhejiang Beilun Power Plant and Brazil’s Grajau 500kV GIS.VFTO seriously threatens the insulation of GIS substations,so it is necessary to pay attention to VFTO.There are two shortcomings in the current VFTO research field:the VFTO phenomenon is related to the sequence and position of the switching operation.Due to the variety of switching operations of the GIS station,manually setting up the VFTO simulation model for all switching operation modes is complex and difficult,requiring the operator to have a higher transient simulation capability;VFTO is a kind of non-stationary signal,so Fourier transform cannot describe the change of its frequency with time.Therefore,proper time-frequency analysis methods are needed to meet the requirements of VFTO spectrum analysis.In view of the above two insufficiency,this paper starts with the VFTO automatic modeling method and the VFTO quadratic time-frequency analysis method.Firstly,this paper studies the VFTO model and simulation analysis method.It is used as the theoretical basis for the VFTO automatic modeling method and the quadratic time-frequency analysis method.The equivalent model of the electrical components in the GIS substation and the model parameters under different voltage levels are performed.This paper analyze the characteristics of VFTO and the simulation method of VFTO repeated breakdown process with a 500kV GIS substation in Shandong Province and UHV VFTO test circuit.Then a VFTO automatic modeling and simulation method based on IEC 61850 SCD file is proposed.By inputting the SCD file and simulation model parameters,the VFTO model is automatically built and simulated in batches to obtain the most severe VFTO waveform and the corresponding isolation switch operation mode.Based on this,the VFTO automatic modeling and simulation software was developed,and the above operations were integrated through the MATLAB GUI interface to realize the visualization operation.The simulation process and simulation results were displayed through the GUI interface.Finally,the quadratic time-frequency analysis method of VFTO is studied.The spectrum characteristics of VFTO are analyzed by using NSTFT-WVD transform.The performance of NSTFT-WVD transform and other time-frequency transforms are compared by VFTO synthesized waveforms and field test waveforms,and the excellent time-frequency analysis performance of NSTFT-WVD transform is verified.Based on NSTFT-WVD transform,the influence of the type of isolating switch and arresters on VFTO spectrum is analyzed.Compared with the traditional manual modeling method,the VFTO automatic modeling method greatly reduces the simulation difficulty of substation design and operation personnel.Under the appropriate selection of component parameters,it can accurately simulate various operating conditions in the substation and meet the needs of engineering practice.As an improved algorithm of the quadratic time-frequency analysis method,the NSTFT-WVD transform has higher time-frequency resolution than the STFT,SPWVD,wavelet transform,and generalized S-transform,and can eliminate cross-term interference in the WVD transform.The NSTFT-WVD transform is suitable for time-frequency analysis of VFTO waveforms.It can obtain time-frequency spectrum and frequency slice diagrams of VFTO waveforms.It has excellent time-frequency analysis performance,which helps researchers to further study the coupling mechanism of VFTO with primary and secondary devices through VFTO spectrum analysis. |
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