Abstract: A new type of transformer remanence detection and degaussing instrument is introduced, which is applied to detect the remanence and conduct the degaussing tests for several 220 kV transformers, and it is found that the remanence rate after the electrical test of the main transformer is much greater than the initial remanence rate after power failure. The core remanence can be gradually reduced by short-circuiting of the winding to ground, but it takes a long time and can not meet the requirements of on-site power transmission. By using transformer remanence detection and degaussing instruments for multiple degaussing, the actual remanence rate of transformer before power transmission can be reduced to a very low value, and the high-voltage excitation current can also be significantly reduced during power transmission. Such an instrument, combined with the existing phase-based closing technique, is available to effectively reduce the incidence of inrush current during no-load closing of main transformer and improve the success rate of power transmission via main transformer.