Research On VFTO Simulation In Disconnecting Switch Time-varying Capacitance Model

In power system,very fast transient over-voltage?VFTO?is a common overvoltage generated during the operation of disconnector,which will damage the insulation safety of gas insulated switchgear?GIS?and bring hidden trouble to the stable operation of power system.Numerical simulation is an important method of VFTO research due to its operability and flexibility.In this paper,the disconnecting switch in VFTO simulation is taken into account and the time-varying capacitance disconnecting switch model is proposed considering the time dependent capacitance effect in the operation,as well as the waveform and characteristics of VFTO is analyzed and studied deeply.Firstly,the disconnecting switch model and VFTO theory is analyzed,and in which the disconnecting switch transient and steady-state phase fracture stage model theory have been deducted.The presence of C_d---dynamic contact capacitance to ground,C_j---static contact capacitance to ground and C_s---contact gap capacitance are pointed out in disconnecting switch and the influence of electric capacity on VFTO characteristics are demonstrated.The current arc resistance model and the arc inductance model are introduced in detail.Moreover,the basic theory of VFTO production and the detailed process of multiple break-down are analyzed.Secondly,the electric field distribution of 1100kV disconnecting switch break-brake process is calculated based on finite element theory,in which the conditions of excitation and boundary are disposed based on suspension conductor method,capacitors are solved based on electric field energy method.The expression is modified based on the initial capacitance of the switching operation.Finally,the VFTO characteristics are analyzed based on the precise disconnecting switch model.The realization method of time-variable capacity and multiple breakdown model in ATP-EMTP is mainly analyzed,as well as the typical test circuit of VFTO is established.In the single breakdown and the whole process of VFTO,the VFTO characteristics of the time-varying capacitance disconnecting switch model,the fixed capacitance model and the resistance-inductor model are compared and analyzed.The influence of initial phase angle,resistance and ferrite magnetic ring on the VFTO characteristics is studied.It is shows that inhibition effect of switching resistor and ferrite magnet ring on VFTO.The time-varying capacitance disconnecting switch model have difference number of breakdown,bus residual and peak voltage compared with the traditional model.The accurate disconnecting switch model considering the whole operate process of disconnecting switch and gap capacitance changes,which have improvement effect on VFTO process simulation.