A static var compensator is a power quality device that uses power electronics to control reactive power flow in the connected system. Therefore, it can provide reactive power compensation with fast response to the power system. In other words, the output of the static var compensator is adjusted to exchange inductive or capacitive currents to control power system variables such as bus voltage. Furthermore, the term static is used to distinguish static var compensators from their rotating counterparts such as synchronous generators and/or electric motors.
Since the 1970s, static var compensators have been used primarily to mitigate voltage fluctuations and the resulting flicker. Today, large industries, especially steel mills, often use static var compensators in electric arc furnace installations to compensate for flicker.
In addition, static var compensators are installed at appropriate locations in the power system to enhance its transfer capability by improving voltage stability while maintaining a smooth voltage curve under different system conditions. Static var compensators can also mitigate active power oscillations through voltage amplitude modulation. In addition, as an automatic impedance matching device, they have the added benefit of bringing the system power factor closer to unity.
Therefore, static var compensators are often installed near high and rapidly changing loads, such as electric arc furnaces, welding plants and other application of VFD in industries prone to voltage fluctuations and flicker. In addition, other benefits of static var compensators include: maximized power compensation; near-instantaneous response to system voltage changes; increased customer economics; use of appropriate shunt filters to eliminate harmonics and reduce voltage distortion; load balancing.
Static var compensators regulate voltage by controlling the reactive power absorbed from or injected into the power system. For example, it generates reactive power by switching capacitor banks when the system voltage is low or the load is inductive. Therefore, the reactive power demand of the lagging load is provided by the static var compensator, which relieves the transmission of the distribution line. Therefore, the voltage drop decreases and the voltage at the load terminal should increase. Likewise, when the system voltage is high or the load is capacitive, the static var compensator absorbs reactive power. In this case, the static var compensator uses a reactor to dissipate the VAR in the system, thereby reducing the system voltage.