Circuit Modeling Of L Shape Elbow,Stents,Spacers Of The GIS Pipe

With high amplitude and broadband electromagnetic waves caused by switching operation propagating in gas insulated switchgear(GIS)pipe,vary fast transient over voltage(VFTO)will be produced in GIS.The leakage of the waves from the pipe leads to strong transient enclosure voltage(TEV)rise relative to the earth.Field distribution of electromagnetic wave propagating in GIS can be distorted locally at the discontinuous/abrupt positions like elbows,spacers and bushings.The pipe stents of GIS are used to supporting GIS pipe.The impedance of pipe stents will be changed because of skin effect and proximity effects with frequency increasing.Setting up equivalent circuit model of pipe elbow,pipe stents and basin-type insulator correctly is very important to study the VFTO and the TEV.The equivalent circuit models of pipe elbow,pipe stents and spacers have been established in this thesis.The effect of such distortion at the discontinuous/abrupt positions like elbows and spacers is usually regarded as a lumped circuit element inserted into the transmission line model.For L-type elbow of GIS pipe,both ?-type and T-type equivalent circuits consisting of compensation capacitance and compensation inductance are investigated.Based on the two-port network parameter obtained by electromagnetic simulation of the L-shaped pipe,the formulae of both the compensation capacitance and inductance are derived by using transmission line theory.For spacers of GIS pipe,the static capacitance calculated by electromagnetic simulation is used to model spacers.Based on the impedance parameters of the conductors of different structures extracted by ANSYS Q3 D Extractor,an approximate calculation method of broadband impedance is proposed for different spacers and the validity of the method is verified.