De-rating of Transformers under Non-sinusoidal Loads: Modeling and Analysis

When supplying transformers under non-linear loads, electromagnetic losses including core loss and copper losses are increased. This results in boasting temperature and consequently reducing transformer lifetime due to the insulation deterioration. To solve the problem, the rated capacity of the transformer connected to a harmonic load is usually reduced which is called the de-rating of transformer. In the present paper, the conventional method for calculating de- rating of transformer is introduced first and its essential equations are given. Based on finite element method (FEM), a new method is then developed for de-rating determination. To evaluate the proposed methods, the simulation and experimental results are presented for a 2 KVA single-phase transformer.