Single-phase transformers are simple in structure, small in size, low in loss, mainly due to small iron loss, and are suitable for application and promotion in low-voltage distribution networks with low load density. Single-phase transformers are widely used in developed countries, such as the United States and Japan. Single-phase power supply has become the main way for residents to supply power. Under this kind of propaganda, some people think that single-phase power supply has the magic power of "loss reduction", and think that single-phase power supply has the magic power of "loss reduction". Phase transformers are more energy-efficient than three-phase transformers, and it is believed that single-phase power supply systems are superior to three-phase power supply systems. In fact, the single-phase transformer and single-phase power supply system are only supplementary forms of the current three-phase power supply system. Due to the constraints of its own characteristics, it can only be applied to certain specific fields.