Abstract:Three-phase unbalance not only reduces the power supply capacity of low voltage distribution network, but also increases its line loss rate. This paper derives the line loss calculation formula expressed by the three-phase unbalance rate and maximum phase current. With the constraint condition of without overload, the paper calculates the influence of three-phase unbalance rate on distribution transformer and low voltage line’s line loss rate. The results show that three-phase unbalance hasn’t an obvious effect on distribution transformer’s line loss rate but has a greater impact on low voltage line’s line loss rate. Furthermore, the article also discusses the engineering governance measure of three-phase unbalance. It provides a decision-making reference for distribution network planning and construction, and operation management.