| The power resources and demand of our country are in reverse distribution, UHV power transmission technology can effectively improve the energy distribution imbalance problems. With the construction of UHV projects ongoing, gas insulated substation (GIS) has been more and more widely used in the high voltage level. When the disconnector in GIS at the time of opening and closing operations, it may occur multiple reignition and breakdown. It will produce high frequency, high am-plitude and short rise-time overvoltage in GIS, also known as the very fast transient overvoltage (VFTO). This overvoltage is very harmful to GIS equipment and the transformer insulation. Given the variability of VFTO, electrical equipment manu-facturers both at home and abroad are still not issued the VFTO insulation standards at present. Since the phenomenon of VFTO in GIS has been found, how can GIS equipment and large power transformer withstand the VFTO impact and how to eliminate the VFTO influence have been concerned by equipment manufacturers and power departments. For this purpose, the paper studied the VFTO calculation meth-od in UHV GIS and transformer.First of all, this paper analyzed the causes of VFTO in GIS, the method of VFTO simulation and the GIS transient model. According to the existing research, the model and parameters of the 500kV voltage grade GIS electrical equipment are sorted out, and the validity of the simulation method is verified by comparing the reference documents. An actual 500kV GIS simulation model is established in the PSCAD/EMTDC software, and the VFTO waveforms of the two operation modes are calculated. Secondly, according to the frequency characteristic of VFTO, a com-plete multiconductor transmission line model is established. The type of transmission line model is defined in this paper, the analytical calculation method of resistance, inductance, conductance and the finite element calculation method of capacitance are also have been given out. By using the finite element analysis software ANSOFT, the inter turn capacitance and the inter disc capacitance in the continuous winding and the inner shielded winding were calculated, and the correctness of the ANSOFT software using method was verified by the simulation results of plate capacitor. In this paper, a frequency-domain algorithm for the potential distribution of the trans-former windings under VFTO is presented, and the algorithm is programmed by MATLAB. By comparing with the simulation results in Simulink, it is proved that the algorithm is correct and the program is correct. At last, the VFTO calculation re-sults in the model of the continuous winding and the inner shield winding are given as the example.In this paper, the finite element software is used to calculate the distributed ca-pacitance of the winding. Compared to the traditional formula, the result is more ac-curate. In order to solve the problem of matrix diagonalization in the process of solving the transmission line equation, the.matrix is simplified as a real symmetrical matrix by the reasonable choice of the distribution parameters, and the numerical stability of the calculation process is achieved. The parameter setting method of IFFT is studied in this paper, in order to avoid the time aliasing caused by the trans-formation of the function from frequency-domain to time-domain. The validity of IFFT is verified by sine wave excitation, and the simulation results show that the calculation error is less than 0.1%. Compared with other methods, this method does not simplify the transfer function, retained the advantages of the transmission line in electromagnetic process description, and the error may occur in the process of sim-plification will be avoid.The research results in this paper can simulate the VFTO in GIS and transformer, which can provide reference for transformer to withstand the VFTO impact. It is of great practical significance and application needs to improve the reliability and economy of the transformer. |
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