1.Why is reactive power compensation necessary?

Reactive power is by no means useless power. In AC power supply systems, inductors and capacitors serve as essential loads. Ferromagnetic loads—such as electric motors and transformers—cannot function without inductive reactive power for excitation; meanwhile, long-distance transmission lines possess inherent capacitive characteristics, effectively acting as shunt capacitors connected to the system during operation. Clearly, reactive power plays an irreplaceable role in energy transmission and exchange; without this exchange, the system cannot operate normally.

To alleviate the reactive power supply burden on power plants, capacitors can be installed at nodes within the power supply system where inductive loads are concentrated, allowing for the local provision of reactive power. Users should design and install reactive power compensation devices—building upon efforts to improve their natural power factor—that can switch in or out in response to load and voltage fluctuations. This prevents the back-feeding of reactive power while raising the power factor to meet national standards, thereby avoiding penalty charges from the power supply utility. Consequently, for both power supply utilities and industrial consumers, implementing automatic reactive power compensation to improve the power factor and prevent reactive power back-feeding is of great significance for conserving energy and enhancing operational quality.

2.Basic principles of reactive power compensation

The reactive loads commonly found in systems are predominantly inductive. When capacitive and inductive loads are connected in parallel to the same circuit, they exchange energy: the capacitive load releases energy while the inductive load absorbs it, and vice versa. The reactive power required by the inductive load can be compensated locally by the reactive power output of the capacitive device, thereby achieving reactive power balance, reducing line losses, enhancing load-carrying capacity, minimizing voltage drops, and alleviating the supply burden on power plants.

3.Forms of reactive power compensation

1) Individual Compensation
Capacitors are installed to compensate individual pieces of electrical equipment locally; they are connected directly to the same electrical circuit and are switched on or off simultaneously with the equipment via the same switch. This method offers optimal compensation, avoids over-compensation during no-load conditions, and ensures power supply quality. It is commonly used for equipment such as high- and low-voltage motors. A disadvantage is the relatively low utilization rate of the capacitors when the equipment does not operate continuously.

2) Distributed Compensation
Capacitor banks are installed on the branch feeder circuits within workshop distribution rooms or substations. They can be switched in groups based on load fluctuations. While this method provides good compensation results, the installation cost is relatively high.

3) Centralized Compensation
Capacitor banks are installed centrally on the primary or secondary busbars of the substation. This method offers simple installation and reliable operation; however, the compensation effectiveness is lower than that of the other two methods, and the cost is also relatively high.

4.Benefits of Reactive Power Compensation

1) Improving Power Factor
Inductive reactive power is compensated by capacitive reactive power, leading to a significant increase in the power factor (vector diagram omitted).

2) Reducing Transmission Line and Transformer Losses
Proper compensation effectively lowers system current. Reducing losses in lines and transformers while conserving active energy constitutes a vital energy-saving measure. In sectors such as the petroleum industry, where transmission lines are long and complex, the installation of reactive power compensation equipment can substantially reduce operating currents and line losses.

3) Increasing Grid Transmission Capacity and Equipment Utilization
Compensation devices effectively reduce system current and apparent power, thereby lowering capacity requirements for grid infrastructure and reducing investment costs. For systems with a power factor around 0.7, appropriate compensation can reduce current by approximately 30%, effectively increasing the load-carrying capacity of power plants and power distribution facilities by 30%.
Installing reactive power compensation devices can resolve issues where transformer or line capacity is insufficient. Balancing reactive power locally reduces the current flowing through lines and transformers, slows insulation aging, extends equipment lifespan, and frees up surplus capacity in transformers and lines.

4) Improving Voltage Quality
A large number of inductive loads in a system causes voltage drops along the lines, particularly at the load ends. Proper compensation effectively mitigates voltage drops and improves power quality. Fluctuations in reactive power significantly impact voltage levels; a reduction in reactive power (Q) leads to a corresponding decrease in voltage loss. For lines experiencing low voltage at the load end, adding reactive power compensation devices can effectively boost voltage, ensuring the safe and reliable operation of equipment.
Furthermore, the widespread use of automated control equipment and non-linear loads in industry introduces harmonics into power distribution networks, causing grid pollution. Properly configuring compensation and filtering equipment suppresses or drastically reduces the impact of harmonics on the power supply and consumption system, serving as a key method for improving power quality.

5) Saving on Electricity Costs
Proper compensation ensures the power factor at the metering point meets national standards, thereby avoiding penalties for low power factor and significantly reducing the user's electricity expenses.