The paper expatiates the principle of a main transformer outage

and discusses the formula of main transformer active loss and economic load. According to the power grid operation data

the loss is compared and benefit is analyzed considering different operation mode of transformer substation. The paper gives example of Yongzhou in Hunan

making the statistical analysis of region 220 kV substation load. Considering shutting down a main transformer in certain months for the substation carrying light load in a long time

the paper calculates the economic benefits for saving the no-load loss for a main transformer

which provides references for economic operation of the regional power grid.