Transformer protection based on the physical parameter model

The influence of the magnetizing inrush is eliminated by the existing transformer protection principles based on the transformer model. However, the errors caused by the imbalance of winding parameters may result in the mal-operation of protection. Based on the loop equations of transformer model, utilizing the unbalanced current in the delta windings to contact the three phases loop equations, the physical parameter model loop equation is obtained to represent the normal running transformer. The novel model takes into account the influence that a random phase of delta windings acts on the other two phases of primary and secondary windings. According to the characteristic that the equation is not valid while the change of winding parameters due to the occurrence of internal faults, a novel transformer protection principle based on physical parameter model loop equation is proposed. The test results that the proposed principle can recognize internal faults reliably and quickly, rising superior to the magnetizing inrush.