Abstract: The configuration of capacitor banks is generally based on 10%~30% of the capacity of the main transformer. Some substations have low load rates, and the reactive power demand is greatly affected by seasonal and day night load fluctuations. However, the main transformer configuration has fewer groups of parallel capacitor devices, with a large single group capacity. There are problems such as insufficient or excessive compensation, and insufficient or excessive compensation, which cannot achieve on-site reactive power balance and reduce losses. Secondly, constrained by the traditional single "voltage power factor" control mode, the power factor fluctuates greatly during light load operation of transformers, which easily leads to frequent switching and reactive power reversal of capacitor banks, causing significant impact on the power grid and making it difficult to effectively achieve reactive power optimization control. This article analyzes the fluctuation data of load and reactive power demand in 35~110 kV substations, and develops a solution for fine grouping and automatic switching of parallel capacitor devices to solve the problems of insufficient reactive power compensation and low power factor.