Low-voltage power distribution systems contain many inductive loads, such as transformers and motors, which rely on electromagnetic fields to transfer or convert energy. During this energy conversion process, the power absorbed by the device windings within a single cycle is equal to the power returned to the source. This represents energy conversion, with no energy consumption. This type of power is called inductive reactive power. Its current phasor lags the voltage phasor by 90°. Similarly, when a capacitor is connected to an AC power grid, the energy absorbed during charging and released during discharge within a single cycle is equal. This also represents energy conversion, with no energy consumption. This type of power is called capacitive reactive power, with its voltage phasor lagging the current phasor by 90°.
Therefore, the capacitive reactive power of a parallel capacitor can be used to compensate for inductive reactive power, reducing the reactive power transmitted by the grid. This improves the power factor, enhances voltage quality, reduces power losses, and increases grid energy delivery.
Classification of reactive power compensation methods for low-voltage power grids. Reactive power compensation methods for low-voltage power grids can be categorized as centralized and decentralized based on the installation method. They can also be categorized as fixed and automatic (automatic) based on the control method (switching mode). ① Centralized compensation involves concentrating capacitors at a single location within the low-voltage power distribution system (typically within the distribution room) to compensate the entire system. ② Decentralized compensation involves distributing capacitors around inductive loads (such as motors and welding machines) and switching them on and off simultaneously with the inductive loads for on-site compensation. ③ Fixed compensation involves using capacitors with fixed capacity, switching them on and off simultaneously. ④ Automatic compensation involves using an automatic switching device to automatically adjust (switch) the compensation capacity of capacitors based on the power factor or reactive power, keeping the power factor of the low-voltage power grid within acceptable limits.