Abstract:The starting/standby power of four units of a power plant is supplied by an external single power source. In order to solve the failure of the external single power line, In order to solve the problem that the unit will lose the standby power supply after the fault of the external single power line, the operation safety risk is high, and the unit will use the external network to purchase electricity during the normal maintenance and start-up period, and the purchase cost is high. Through the feasibility study of reformation of 6kV auxiliary power system in various ways, three reformation schemes of 6kV auxiliary power system are put forward. Through comprehensive technical discussion and scheme demonstration of their advantages and disadvantages, the factors such as investment cost, construction conditions and equipment condition are considered comprehensively. Finally, 6kV auxiliary A and B of unit 1-4 are adopted. Segments are transformed by means of parallel connection between cables and 6kV common C (D) segments. The technical renovation of 6kV auxiliary power system was completed in 2017, and the feasibility and superiority of the scheme were verified after one year operation. The modification not only greatly improves the flexibility of the operation mode of the plant system, the safety and economy of the unit operation, eliminates the security risks caused by the power failure of the startup power supply, but also realizes the power supply of the operating unit to the outage unit, saves the purchased power and reduces the operation cost, and minimizes the purchased power.