The Port Wideband Equivalent Circuit Model Of 1000kV UHV AC Transformer

As the key equipment in UHV transmission project,UHV AC transformers have more complicated technical issues than low voltage transformers because of their high voltage and large volume.During the UHV AC system operation,the over-voltage of the UHV AC transformers can be over-voltage due to the over-voltage caused by the operation of circuit breakers and disconnecting switches,lightning over-voltage generated by lightning strikes and the like.Therefore,it is necessary to establish a broadband model of UHV transformer to provide the necessary conditions for electromagnetic transient simulation and over-voltage analysis of transmission system.In this paper,the 1000kV UHV AC transformer is taken as the research object.Under the conditions of thunder and lightning overvoltage,the port broadband modeling,parameter calculation,simulation and comparison of broadband model and electromagnetic transient conventional model under different engineering application scenarios are studied.Firstly,the structure of UHV AC transformer is introduced,and the frequency?domain measurement method of impedance wide-band impedance is studied.The influence of lead wires is eliminated by "open circuit,short circuit and load verification”.The theoretical analysis shows that different wiring methods The measurement method of the UHV AC transformer is introduced.The equivalent method of the impedance measurement of the remaining ports when the transformer port is struck by lightning is described.Then,the modeling principle of single-port broadband equivalent circuit model is illustrated.The vector matching and passive correction method are used to fit the admittance to the rational function,and then the port wideband equivalent circuit is established according to the network synthesis method.The input capacitance model compares the frequency domain and the time domain,and focuses on the peak and rising edge of the port voltage in the time domain simulation.Finally,the dual-port broadband modeling and parameter calculation combined with the low-frequency magnetic model and the high-frequency correction model are introduced.The two-port broadband equivalent circuit model is simulated in the time domain,verified with the time-domain measurement results,The correctness of the model is compared.The simulation results of the dual-port broadband equivalent circuit model and the dual-port low-frequency magnetic model are compared to show the correctness of the model.