Why Reactor match with the Capacitor?

The Function of Series Reactors
In power transmission and distribution systems, there are many harmonic sources, such as large-power thyristor rectifiers and regulators, electric arc furnaces, etc. If parallel capacitors are directly connected, the change of circuit parameters often leads to the amplification of system harmonic components, and in severe cases, resonance may occur. High-voltage parallel capacitor banks are usually connected with series reactors of a certain reactance rate to suppress the harmonic amplification caused by the connection of capacitors to the power grid.

The closing inrush current of the capacitor
The voltage across the capacitor cannot change abruptly. At the instant when the capacitor is connected to the power grid, it behaves like a short circuit. Especially when the capacitor is paralleled with the operating capacitor bank, a high-frequency and high-amplitude transient overcurrent will be generated, which is called the inrush current. The magnitude of the inrush current is related to the short-circuit capacity of the busbar at the connection point of the capacitor bank.

Limitation requirements for closing surge current
Based on the principle that the current through an inductor cannot change abruptly, by connecting a capacitor bank in series with an inductor, the closing surge current generated when the capacitor bank is connected to the power grid can be effectively limited.
When the short-circuit capacity of the bus at the connection point of the capacitor bank does not exceed 50 times the capacity of the capacitor, the closing surge current of a single capacitor bank does not exceed 10 times the rated current of the capacitor. High-frequency and high-amplitude surge currents can cause damage to capacitors, contacts of switchgear and other equipment in the circuit. According to the operating experience of domestic power systems over many years, it has been found that when the closing surge current of the capacitor device is 20 times the rated current of the capacitor, there is no damage to the circuit equipment. Therefore, the limitation of the surge current should be taken as 20 times. When it exceeds this value, it should be restricted.

Classification of Series Reactors in Practical Use
Firstly, there are series reactors mainly used to limit the amplification of power harmonics. The connection of such series reactors can effectively suppress the amplification of certain power harmonics in the system. For example, a 5% series reactor can suppress harmonics of 5th and above orders, and a 12% series reactor can suppress harmonics of 3rd and above orders. These reactors all have relatively high inductance values and can effectively suppress the peak value and frequency of inrush current.

Secondly, for scenarios without harmonic issues or where harmonic problems are not prominent, a dedicated series reactor specifically designed to limit the inrush current upon closing can be selected. Here, the two key features of the series reactor are: Firstly, the reactance rate is low, typically ≤ 1%. Secondly, its configuration with capacitor banks is relatively convenient and flexible. As long as the limit on the inrush current multiplier meets the standards, it is acceptable.

Latest Advancements

Smart tuning: Dynamic reactance adjustment via IGBT

Integrated designs: All-in-one cabinets (capacitor + reactor + switch, e.g., hybrid SVG systems)

Note: Series reactors are mandatory when background harmonic voltage distortion exceeds 3%, otherwise capacitor lifespan may reduce by >50%.

Hubei Jineng Electric Power Technology has been dedicated to the electrical industry for 20 years, with rich experience and technical accumulation. It can meet the diversified and customized demands of customers and provide them with efficient and economical solutions. Intelligent capacitors, wound coils, foil-wound reactors, APF, SVG, intelligent controllers, circuit breakers, all are self-developed and self-produced. For more information, please visit our website：www.chnjn-electric.com