Calculation Of Overvoltage Under Transformer Winding VFTO Based On Overlapping Partition Wavelet Relaxation Algorithm

Action isolation switches,operating breakers,or short-circuit faults are most likely to cause very fast transient overvoltage(VFTO)in gas insulated substations(GIS).The rising edge of VFTO is very steep,and the rise time is usually only nanoseconds.However,VFTO contains a large-scale harmonic component with a very wide frequency domain.This transient voltage wave invades the transformer coil and causes a very uneven voltage distribution.In addition,taking into account the presence of other equipment,it may also cause high-frequency oscillations inside the transformer,which will cause damage to the insulation of the transformer coils,causing great economic losses.Therefore,it is very important to analyze the potential distribution of transformer winding under VFTO.With the increase of transformer size,the number of conductors has become the main factor that limits the calculation speed in wave process calculations.Based on this background,a multi-conductor transmission line(MTL)model based on transformer windings is used to study the time-domain fast algorithm for transformer winding wave process calculation under VFTO.First,the finite element software ANSYS Maxwell and the steps of using the software to calculate the electrical parameters are introduced to obtain the electrical parameter matrix of the transformer winding.Second,the influence of the partition on the waveform relaxation algorithm is introduced,and the multi-conductor partition based on the coupling coefficient is proposed.In the strategy,the multi-conductor system is divided into smaller-scale systems based on the capacitance coupling coefficient and the inductive coupling coefficient,and the oil-immersed continuous winding in the laboratory is used as the experimental equipment to verify the conclusions obtained;then,combining the time-domain finite element method with the wave relaxation algorithm,the calculation model of the multi-conductor transmission line is deduced,and the resulting transformer winding partial differential equation is solved in the time domain.The time-domain solution of the voltage and current at each sampling point of the wire is calculated by MATLAB programming;The time-domain solution of the voltage and current at each sampling point of the wire is calculated by MATLAB programming;Finally,the VFTO over-voltage simulation is performed for large tangled transformer windings.Using the modeling method,electric parameter calculation method and differential equation calculation method proposed in the previous chapter,the VFTO impact wave-down process of large entangled transformer windings was simulated and the overvoltage was verified by experiments.Through the comparison between the simulation results and the experimental results,the correctness of the theories and calculation methods proposed in this paper is verified,and it has certain guiding significance for the rapid calculation of transformer winding overvoltage response.