Classification and main use of power capacitors
Power capacitors are capacitors used in power systems and electrical equipment. It is characterized by high power, high voltage and low frequency, so it is huge. In 1926, power capacitors began to be factory-produced and officially applied in power systems. With the establishment of large power plants and long-distance transmission systems, and the development of emerging science and technology fields, the variety and capacity of power capacitors have been rapidly developed. In the early 1950s, the largest single-capacity capacity of parallel capacitors was 25kvar-kvar. By 1978, the largest single-unit capacity had reached 6667kvar, and in the 1980s it had reached a single capacity of 10,000 kilowatts. Currently, power capacitors are moving toward higher capacity.
There are many types of power capacitors. According to their installation methods, they can be divided into indoor and outdoor types. According to their rated voltage, they can be divided into low voltage and high voltage. According to their phase number, they can be divided into single phase and three phase. Except for the low-voltage parallel capacitors, the rest are single-phase; according to the shell material, it can be divided into metal shell, porcelain insulating shell, bakelite cylinder shell, etc.; according to its use, it can be divided into the following eight kinds.
(1) Shunt capacitor: formerly known as phase shift capacitor. It is mainly used to compensate the reactive power of the inductive load of the power system to improve the power factor, improve the voltage quality and reduce the line loss. Single-phase shunt capacitors are mainly composed of the core, the outer casing and the outlet structure. The metal foil (as a plate) is wound up with an insulating paper or a plastic film, and a plurality of components, insulators, and fasteners are press-fitted to form a capacitor core, and the insulating oil is immersed. The lead wires of the capacitor plate are led to the outlet connection piece at the lower end of the outlet porcelain sleeve after being connected in series and in parallel. The metal casing of the capacitor is filled with insulating medium oil.
(2) Series capacitors: connected in series in power frequency high-voltage transmission and distribution lines to compensate the distribution inductance of the line, improve the static and dynamic stability of the system, improve the voltage quality of the line, lengthen the transmission distance and increase the transmission. Capacity. Its basic structure is similar to a parallel capacitor.
(3) Coupling capacitor: It is mainly used for high-frequency communication, measurement, control, protection of high-voltage power lines and components used in devices for extracting electric energy. The high voltage end of the coupling capacitor is connected to the power line, and the low voltage end is grounded via the coupling coil, so that the high frequency carrier device is coupled to the high voltage line at a low voltage. The coupling capacitor case is composed of a bottom and a cover made of a porcelain sleeve and a steel plate. A dilator made of thin steel plate is placed in the outer casing to compensate for the change in the volume of the impregnant with temperature.
(4) Circuit breaker capacitor: formerly known as voltage equalizing capacitor. It is mainly used for parallel voltage equalization on the fracture of the ultra-high voltage circuit breaker, so that the voltage between the fractures is uniform during the breaking process and disconnection, and the arc-extinguishing characteristics of the circuit breaker can be improved and the breaking capacity can be improved. The structure of a commonly used circuit breaker capacitor is similar to that of a coupling capacitor. With the development of high-voltage ceramic capacitors, ceramic capacitors have been used as capacitive components, and then casings made of porcelain sleeves and steel plates are used to form circuit breaker capacitors.
(5) Electrothermal capacitor: used in an electric heating system with a frequency of 40 Hz & mdash; 24000 Hz to improve the power factor and improve the voltage or frequency of the circuit. Electric heating capacitors must have a good heat dissipation due to their large amount of heat. Usually, the plates are cooled by water. Applicable to electric heating capacitors above 4000Hz, the outer casing is welded with brass plate.
(6) Pulse capacitor: It mainly functions as a storage energy. It is charged by a power source with a small power for a long period of time, and then oscillated or discharged without oscillating in a short time, and a large impact power can be obtained. Pulse capacitors are widely used, such as basic voltage energy storage components such as surge voltage generators, surge current generators, and circuit breaker test circuit breakers.
(7) DC and filter capacitors: used in high voltage DC devices and high voltage rectifier filter devices. An AC filter capacitor can be used to filter out higher harmonic components in the power frequency current.
(8) Standard capacitor: used in the power frequency high-voltage measurement medium loss circuit, as a standard capacitor or as a capacitor voltage divider for measuring high voltage. Standard capacitors require accurate and stable capacitance values, so gas and double shielded coaxial cylindrical and concentric spherical plate systems are often used.