Principle and Usage of Power Capacitors

Power capacitors are used in electrical systems and electrical equipment. Any two pieces of metal conductors, separated by an insulating medium, constitute a capacitor. The capacitance of a capacitor is determined by its geometric size and the characteristics of the insulating medium between the electrodes. When a capacitor is used under alternating current voltage, its capacity is often represented by its reactive power, in units of vars or kilovars.

Shunt capacitors are a type of reactive power compensation equipment connected in parallel to the line. Their main function is to compensate for the reactive power of the system, improve the power factor, thereby reducing energy loss, enhancing voltage quality, and equipment utilization.

Series capacitors are primarily used to compensate for the inductance of the power system, often used in high-voltage systems.

Classification of Power Capacitors

Power capacitors are classified based on installation type, rated operating voltage, phase number, and outer shell material. They can be indoor or outdoor; based on their rated operating voltage, they are categorized into low voltage and high voltage; by phase number, they are either single-phase or three-phase, with low voltage shunt capacitors being an exception as the rest are single-phase; and according to the outer shell material, they can have metal shells, ceramic insulated shells, bakelite tube shells, among others.

Based on their applications, they can be divided into the following eight types:

Shunt Capacitors: Previously known as phase-shifting capacitors. They are primarily used to compensate for the reactive power of inductive loads in power systems, to improve power factor, enhance voltage quality, and reduce line loss.

Series Capacitors: Connected in series with the power frequency high-voltage transmission and distribution lines to compensate for the line's distributed inductance, improving the system's static and dynamic stability, enhancing the voltage quality of the line, extending the transmission distance, and increasing the transmission capacity.

Coupling Capacitors: Mainly used for high-frequency communication, measurement, control, protection in high-voltage power lines, and as components in devices extracting electrical energy.

Circuit Breaker Capacitors: Previously known as equalizing capacitors. Connected in parallel with the ultra-high voltage circuit breaker contacts to equalize voltage across the contacts during and after separation, improving the arc extinguishing characteristics of the circuit breaker and enhancing its breaking capacity.

Electric Heating Capacitors: Used in electric heating systems operating at frequencies from 40 to 24,000 Hz to improve power factor and the voltage or frequency characteristics of the circuit.

Pulse Capacitors: Mainly serve as energy storage devices used in impulse voltage generators, impulse current generators, circuit breaker testing oscillatory circuits, and other basic energy storage components.

DC and Filtering Capacitors: Used in high-voltage direct current (HVDC) systems and high-voltage rectification filtering devices.

Standard Capacitors: Used in power frequency high-voltage measurement of dielectric loss circuits as standard capacitors or as capacitive voltage dividers for measuring high voltage.