Calculation method of winding eddy‐current losses for high‐voltage direct current converter transformers

Abstract

In this paper, a correction method is introduced to make a more accurate calculation of winding eddy-current losses of high-voltage direct current (HVDC) converter transformer. The assumption that winding eddy-current losses of HVDC converter transformers follow the frequency with the exponent 2 proposed by IEC 61378-2 Std. is thought to be inappropriate and the skin effect should be taken into consideration. The frequency characteristic of winding eddy-current losses is proposed by analysing the distribution of magnetic flux in conductors, in which skin effect is taken into consideration. The correction method with a correction factor is then introduced to correct the assumption. To verify the validity of the correction method, a two-dimension axisymmetric finite element analysis of a HVDC converter transformer is conducted. The geometrical complexity of windings and electrical connection are fully taken into account, it is shown that the correction method shows a significant advantage. Influence of different methods is revealed by applying the actual non-sinusoidal load current and it is shown that the error of correction method is the least. At last, harmonic losses measurements are conducted on three coils to investigate the limits of the correction method.