A new method for testing winding material of an oil-immersed three-phase transformer was proposed based on the principle of thermocouple.In this method

the winding material is recognized by detecting the parasitic thermocouples which only exist in the transformer with non-copper windings.An asymmetric electric heating mode was presented to generate temperature difference among the phases of the windings

and then the parasitic thermocouples could be found out by detecting the corresponding thermal electromotive forces.In order to verify the feasibility of the proposed testing method and acquire appropriate heating time

the temperature distribution in transformer and the theoretical values of the thermal electromotive forces were numerically computed.Testing results of the transformers with respective aluminum and copper windings verified the effectiveness of the winding material testing method.This method requires no special devices

and it is simple and applicable to other power equipment with windings.