In modern buildings, the 10kV dual-circuit power supply of the ring network cabinet is generally used to enter the line, and the single busbar is segmented, automatically switched, and each other is standby. In some large and super high-rise buildings in some cities, the use of 35kV-level power inlets is also becoming more and more widely used, and direct drop or two-stage voltage drop can be used. The loads in the construction industry are basically low-voltage loads, mainly including lighting, air-conditioning, elevators, office and household appliances, among which single-phase loads account for a relatively high proportion. Therefore, building electrical appliances have large load fluctuations, high harmonic distortion rates, and three-phase imbalances. More serious and other characteristics.