Shunt capacitor, formerly known as phase-shifting capacitor. It is mainly used to compensate the reactive power of inductive load in power system, so as to improve power factor, improve voltage quality and reduce line loss. Single phase shunt capacitor is mainly composed of core, shell and outgoing line structure. A metal foil (as a pole plate) is stacked with insulating paper or plastic film and wound together. A capacitor core is formed by pressing several elements, insulating parts and fasteners, and impregnated with insulating oil. The lead of the capacitor plate is led to the outlet connecting piece at the lower end of the outlet porcelain bushing after being connected in series and parallel. The metal shell of the capacitor is filled with insulating medium oil.
Introduction to shunt capacitor
Most of the power loads in the power grid, such as motors and transformers, belong to inductive loads. In the process of operation, it is necessary to provide corresponding reactive power to these equipment. After the reactive power compensation equipment such as shunt capacitor is installed in the power grid, it can provide the reactive power consumed by the inductive load and reduce the reactive power provided by the power grid to the inductive load and transmitted by the line. Due to the reduction of the flow of reactive power in the power grid, it can reduce the power loss caused by the transmission of reactive power by the line and transformer.
Reactive power, many electrical equipment work according to the principle of electromagnetic induction, such as distribution transformer and motor. They all rely on the establishment of alternating magnetic field to convert and transfer energy. The electric power required to establish alternating magnetic field and induced magnetic flux is called reactive power. Therefore, the so-called "reactive power" is not "useless" electric power, but its power is not converted into mechanical energy and heat energy; Therefore, in the power supply and consumption system, in addition to active power supply, reactive power supply is also required, both of which are indispensable. The unit of reactive power is var.
In the power grid, there are two kinds of electric power supplied by the power supply to the load: one is active power and the other is reactive power. Active power is the electrical power required to maintain the normal operation of electrical equipment, that is, the electrical power that converts electrical energy into other forms of energy (mechanical energy, optical energy, thermal energy). For example, a 5.5kW motor converts 5.5kW power into mechanical energy to drive the water pump to pump water or thresher to thresh;
Various lighting devices convert electric energy into light energy for people's living and working lighting. Reactive power is more abstract. It is the electric power used for the electric field and magnetic field in the circuit, and used to establish and maintain the magnetic field in electrical equipment. All electrical equipment with electromagnetic coils must consume reactive power in order to establish a magnetic field. For example, a 40W fluorescent lamp not only needs 40W active power (the ballast also needs to consume part of the active power) to emit light, but also needs about 80var reactive power for the coil of the ballast to establish an alternating magnetic field. It is called "reactive power" because it does not work externally.
Reactive power is by no means useless power, it is very useful. The motor needs to establish and maintain the rotating magnetic field to make the rotor rotate, so as to drive the mechanical movement. The rotor magnetic field of the motor is established by obtaining reactive power from the power supply. The transformer also needs reactive power to generate magnetic field in the primary coil of the transformer and induce voltage in the secondary coil. Therefore, without reactive power, the motor will not rotate, the transformer will not change voltage, and the AC contactor will not pull in.Under normal circumstances, electrical equipment should not only obtain active power from the power supply, but also obtain reactive power from the power supply. If the reactive power in the power grid is in short supply, the electrical equipment does not have enough reactive power to establish a normal electromagnetic field, then these electrical equipment can not work under rated conditions, and the terminal voltage of the electrical equipment will drop, thus affecting the normal operation of the electrical equipment.Reactive power also has certain adverse effects on power supply and consumption, mainly in the following aspects:
(1) Reduce the output of generator active power.(2) When the apparent power is constant, increasing reactive power will reduce the power supply capacity of power transmission and transformation equipment.(3) The flow of reactive power in the power grid will increase the line voltage loss and power loss.
(4) When the system lacks reactive power, it will cause low power factor operation and voltage drop, so that the capacity of electrical equipment can not be brought into full play.Function of shunt capacitor in compensating reactive power
There are two methods for power capacitor as compensation device: series compensation and parallel compensation. Series compensation is to connect capacitors directly in series to high-voltage transmission lines to improve transmission line parameters, reduce voltage loss, improve its transmission capacity and reduce line loss. The capacitor of this compensation method is called series capacitor, which is applied to high-voltage long-distance transmission lines, and is rarely used by power users. Parallel compensation is to connect the capacitor directly with the compensated equipment to the same circuit to improve the power factor. The capacitor used in this compensation method is called shunt capacitor, which is adopted by power enterprises. There are usually three ways according to the installation position of the capacitor.
1. The centralized compensation capacitor bank is centrally installed on the 6 10kV bus of the enterprise or local general step-down substation to improve the power factor of the whole substation and basically balance the reactive power within the power supply range of the substation. It can reduce the reactive power loss of high-voltage line and improve the power supply voltage quality of the substation.2. For group compensation, capacitor banks are installed on the high-voltage or low-voltage bus of workshop or village terminal substation with low power factor, also known as decentralized compensation. This method has the same advantages as centralized compensation, only the reactive power compensation capacity and range are relatively small. However, the effect of grouping compensation is obvious and widely used.3. Local compensation: the capacitor or capacitor assembly is located near the asynchronous motor or inductive electrical equipment for local reactive power compensation, also known as separate compensation or individual compensation. This method can not only improve the power factor of the power supply circuit for electric equipment, but also improve the voltage quality of electric equipment. It is very suitable for small and medium-sized equipment.
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