A typical type of transformer has two coils. One is called high voltage ( HV) winding and the other is called low voltage ( LV) winding. High quality delta is used in HV winding. As a result , larger bushings are used for HV winding termination. Due to the relatively low voltage in the LV winding, six size bushings are used for termination. So without test, the shape of the bushing of the transformer can be identified as high side or low side.