An on-load test method for the Y/Δ converter transformer base on inrush current

For the Y/Δ converter transformer in the converter station, the transformer has only two windings, and the on load test cannot be implemented to test the polarities of current transformers' (CTs') secondary loops. In order to fill this gap, a novel polarity determination method for the CTs of the Y/Δ converter transformer is presented in this paper. Firstly, the configurations of CTs and relay protections for converter transformer are introduced. Besides, the characteristics of the inrush currents caused by charging the converter transformer is also analyzed. Based on that, a polarity determination method of CTs is proposed. The impact of harmonics on the on-load test data of the converter transformer can be effectively avoided with the proposed method. The proposed approach is validated with the on-load test data of the practical converter transformer.