Influence of DC Remnant Magnetism on the No-load Closing Characteristic of Large Capacity Transformer

Abstract

The DC resistance of transformer winding is too large, which resulting in serious heat. Heating causes the aging of transformer insulation, and ultimately reduces the service life and safe operation of transformers. Therefore, the user department will regularly measure the DC resistance of the transformer. The common measurement method is the constant current method, that is, the direct current is applied to the transformer winding, and the current used by each user is different. After the test, the transformer is put into operation. However, no-load closing after DC resistance measurement often leads to tripping of circuit breaker and failure of power transmission in substation. In order to explore the problem in principle, this paper calculates the remnant magnetism caused by DC current to the transformer; then puts forward a model to calculate the magnitude of inrush current formed by no-load closing transformer with DC remnant magnetism, analyzes the factors affecting the magnitude of the inrush current; studies the method of controlling the inrush current, provides a theoretical basis for the safety of transformer reliable operation.