Calculation and verification for stray loss of transformer copper shield under harmonic excitation

By referring to the harmonic loss calculation method of converter transformer provided by IEC61378-2 standard, an analytical formula for calculating stray loss of transformer copper shield is obtained. Based on the simplified model of P21c-EM1, a new method of stray loss mea-surement is adopted, in which the stray loss in the structure is obtained by subtracting the accurate simulation value of the model excitation coil loss from the total loss mea-surement value of the model. The obtained results are used as experimental values to verify the calculation result of the analytical formula. The results show that the calculative results of the fundamental wave loss of the copper plate are generally consistent with the experimental values. The copper plate loss under the fundamental wave superimposed multiple harmonic excitation is almost the same as the sum of the copper plate loss under each individual harmonic excitation. Under the same excitation current frequency, the stray loss of the copper plate satisfies a certain proportional relationship with the square of the current size. Under the same excitation current size, the relationship between the copper plate loss and the 0.8 times of the current frequency does not satisfy the frequency characteristic given by IEC standard. In these regards, a correction factor that considers the magnetic field distribution is introduced to correct the frequency characteristics. The effectiveness of the correction factor is verified by comparison results obtained from the correction approach and the experimental value. © 2019, Electric Power Automation Equipment Press. All right reserved.