UHV transformer adopts the neutral point voltage regulation mode and the main body of the transformer is connected to the ground through the parallel branch of the voltage regulating winding and the compensation excitation winding. When the DC current flows in（or flows out）the neutral point

the DC magnetic bias characteristic of UHV transformer under different taps has difference:（1）The different number of turns and resistance with corresponding connection at different taps lead to different DC current of the voltage-regulating winding and the compensation excitation winding as well as different saturation level of the cores.（2）The different phase of voltage regulation with corresponding connection at positive and negative adjustment condition of voltage regulation transformer leads to different half wave saturation position of core due to the influence of DC magnetic bias. In this paper

field-circuit coupling method is used to solve the real time voltage and current of each transformer winding

the DC magnetic bias characteristic and their interaction relation of 3 sets transformers at different taps are analyzed by way of joint simulation of the main transformer

voltage regulation and compensation of UHV transformers.