Large-scale petrochemical enterprises have a large power load, usually the total operating capacity is greater than 60MVA, the power supply voltage is (66) 110kV, 220kV, and should be powered by more than two independent power sources. The operation mode is generally dual power supply single operation or dual power supply dual run. Petrochemical companies have very high requirements for the reliability of power supply and distribution. The load is mainly asynchronous motors, which is relatively stable, but the start of large motors has a greater impact on the power supply and distribution system.