The current status and significance of reactive power compensation

In power distribution systems, to reduce line power losses caused by large‑volume reactive current supplied by distribution networks to loads, reactive power compensation devices of corresponding voltage grades must be deployed at each load point. This helps enhance the power grid’s transmission capacity and lower transmission losses. Reactive power compensation for distribution networks has become an indispensable link to ensure the safe and economical operation of power grids.
 
In addition, with the extensive application of high‑power power electronic devices, more harmonics are injected into power grids, resulting in worsening grid pollution and severe degradation of power quality. Traditional static compensation and static passive filtering devices can no longer meet the requirements for improving grid power quality, making dynamic reactive power compensation and harmonic control an increasingly prominent challenge.
 
Overall, the significance of reactive power control and compensation lies in addressing the following four core issues. First, power grids face growing demands for operational efficiency, and on‑site reactive power compensation is required to fully utilize power transmission and transformation capacity. Second, power sources are generally far from load centers; long‑distance power transmission calls for flexible reactive power regulation to tackle stability and voltage control problems. Third, distribution networks contain a large number of inductive loads that consume massive reactive power during operation, leading to heavy losses in distribution systems. Finally, end‑users have gained greater awareness and raised higher requirements for power supply quality. Improving power factor, reducing voltage deviation and disturbances, and suppressing harmonic amplification have become key concerns. Therefore, on‑site reactive power compensation for power grids, especially dynamic compensation, is highly critical in distribution systems.
 
TSC Dynamic Compensation Mode
 
Thyristor‑Switched Capacitor (TSC) or contactor‑switched automatic capacitor banks improve the power factor of grid systems by adding capacitive reactive loads to the power grid. With simple technology and low cost, this is currently the mainstream reactive power compensation method for low‑voltage integrated power distribution systems. Nevertheless, it has several shortcomings. Due to capacitor capacitance allocation constraints, grouped switching provides intermittent and discontinuous compensation for inductive reactive power, which may cause under‑compensation or over‑compensation. Moreover, parallel resonance or harmonic amplification triggered by harmonics seriously endangers the operational safety and service life of capacitor banks.
 
Current Status and Significance of Reactive Power Compensation
 
The Static Var Compensator (SVC) is composed of thyristor‑controlled switched reactors and capacitor banks. It features fast reactive power regulation and smooth adjustment, yet it generates harmonics during operation and needs passive filters for harmonic absorption. High‑order harmonics are likely to occur during switching, and the equipment suffers high power consumption.
 
The Static Var Generator (STATCOM / SVG) is mainly built around a voltage‑source inverter. By properly switching turn‑off power devices, it converts DC voltage on capacitors into three‑phase AC voltage synchronized with power system voltage, which is then connected in parallel to the power grid through reactors and transformers. By precisely controlling the inverter’s output voltage, its operating state can be flexibly adjusted to capacitive, inductive or zero‑load mode. Compared with SVC, STATCOM / SVG boasts faster response speed, lower harmonic current, and can inject large reactive power into the system even under low grid voltage. With technological maturity and cost reduction, STATCOM / SVG has gradually become a vital technical solution in the reactive power compensation industry.