Combination transformer (commonly known as American box transformer) is a type of transformer that combines the transformer body, switchgear, fuses, tap changers, and related auxiliary equipment. The high-voltage wiring scheme includes terminal type and ring network type, which can meet the requirements of various power supply systems. And it has the advantages of compact structure, small volume, low land occupation, low investment, and fast installation. It can be used both indoors and outdoors, widely applicable to residential areas, airports, high-rise buildings, commercial centers, factories, mines, enterprises, hospitals, schools and other occasions. It can penetrate the load center to the maximum extent and improve the quality of power supply. And it can meet various configuration requirements such as user energy metering, reactive power compensation, low-voltage shunting, etc., making it easy and flexible to use.