As a new thing, the Scott transformer with secondary midpoint drawn-out is integrated by traditional Scott transformer and single-phase connection type in AT power supply mode.

Regarding the problems found in electric glass furnaces with Scott power supply which are not completely symmetrical, the author calculates the rules of variation of the equivalent current between the electrodes in this case and analyzes the reasons for the problems.

Based on the electromagnetics analysis of the SCOTT transformer, this paper derives its voltage equations and presents the transformer protection principle, operation equations and operation characteristics.

Based on the principle and fundamental formula of Scott transformer, it presents a internal fault model which composed of 2 single-phase transformers, analyzes the relationship between port voltage of single-phase transformer and power voltage when faults occur and simulates internal fault current and magnetizing inrush current.