Abstract: The UHV transformer includes two parts:the main transformer and the voltage regulating compensation transformer,so its structure is more complex.Accurately grasping the current law of the UHV transformer during power transmission is the key to verifying the protection direction. A single-phase equivalent calculation model for UHV transformers was established,and the numerical relationship of winding currents on each side of the transformer was analyzed using the principle of winding magnetic potential balance.A correlation model of winding currents on each side was established.By using the established model to analyze the protection current of ultra-high voltage transformers,the direction of secondary current can be quickly determined,thus achieving verification of the relay protection direction of ultra-high voltage transformers.Finally,the correctness of the model was verified through actual load testing.According to the debugging requirements of UHV transformers with complex structure,the magnitude and direction of the main transformer and voltage regulation compensation variable protection TA measurement current during the commissioning process of UHV transformer power transmission were analyzed in detail,and a method for determining the polarity of protection TA was proposed.The research results can provide reference for the selection and engineering design of UHV transformers equipment.