Analysis of a novel criterion of transformer protection based on model

A novel criterion of transformer main protection based on model is presented. Firstly, the basic theory of the model based main protection of transformer with Y/Δ connected windings and the problems existing in its application are analyzed, and the primary reason of those problems is pointed out. On the premise that an additional TA is installed to measure the winding current on the delta side, a novel criterion which is associated with each equation separately is presented, which can reflect that the leakage impedances of three windings are not entirely the same. It is needless to calculate the impedances of the windings on each side separately, and there are sufficient reliability and sensitivity under various conditions. The experiment data of transformer under various conditions are obtained by ATP. The correctness of the presented criterion is proved by the experiment results.