What is the use of shunt capacitor reactive power?

Shunt capacitor, 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, insulating members and fasteners are press-fitted to form a capacitor core, and the insulating oil is impregnated. 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.

Introduction to shunt capacitors:

Most of the electrical loads in the power grid, such as electric motors and transformers, are inductive loads, and corresponding reactive power is required to be supplied to these devices during operation. After installing a reactive power compensation device such as a parallel capacitor in the power grid, the reactive power consumed by the inductive load can be provided, and the reactive power supplied by the power supply to the inductive load and transmitted by the line can be reduced, since the reactive power is reduced in the power grid. The flow, therefore, can reduce the power loss caused by the transmission of reactive power to the line and transformer.

Reactive power:

Reactive power, many electrical equipment are based on the principle of electromagnetic induction, such as distribution transformers, motors, etc., they all rely on the establishment of alternating magnetic fields in order to convert and transfer energy. The electric power required to establish the alternating magnetic field and the 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 or thermal energy; therefore In addition to the need for a working power supply, a reactive power supply is required in the power supply system, and both are indispensable. The reactive power unit is Var.

In the power grid, there are two types of electrical power supplied by the power supply: one is active power and the other is reactive power. Active power is the electrical power required to keep a consumer operating normally, that is, the electrical power that converts electrical energy into other forms of energy (mechanical, optical, thermal). For example, a 5.5 kW electric motor converts 5.5 kW of electric power into mechanical energy, which drives pump water pumping or thresher threshing; various lighting devices convert electrical energy into light energy for people to live and work with. Reactive power is abstract, it is used in electric and magnetic fields in circuits, and is used to establish and maintain electrical power in electrical equipment. For electrical equipment with electromagnetic coils, reactive power must be consumed to establish a magnetic field. For example, a 40W fluorescent lamp requires 40W of active power (the ballast also consumes a part of the active power) to emit light. It also needs about 80var of reactive power for the ballast coil to establish an alternating magnetic field. Because it does not work outside, it is called "reactive."

Reactive power is by no means useless power, it is very useful. The motor needs to establish and maintain a rotating magnetic field to rotate the rotor, thereby driving the mechanical motion. The rotor magnetic field of the motor is established by taking reactive power from the power source. The transformer also needs reactive power to generate a magnetic field in the primary coil of the transformer and induce a voltage in the secondary coil. Therefore, without reactive power, the motor will not rotate, the transformer will not be transformed, and the AC contactor will not pull.

Under normal circumstances, the electrical equipment not only needs to obtain active power from the power supply, but also needs to obtain reactive power from the power supply. If the reactive power in the power grid is in short supply, and the power equipment does not have enough reactive power to establish a normal electromagnetic field, then the power equipment cannot be operated under the rated condition, and the terminal voltage of the power equipment is lowered. Affect the normal operation of electrical equipment.

Reactive power also has certain adverse effects on supply and use of electricity, mainly in:

(1) Reduce the output of the generator active power.

(2) When the apparent power is constant, increasing the reactive power will reduce the power supply capacity of the transmission and transformation equipment.

(3) The flow of reactive power in the power grid will cause an increase in line voltage loss and an increase in 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 will not be fully utilized.

Parallel capacitors compensate for the effect of reactive power:

There are two methods for power capacitors as compensation devices: series compensation and parallel compensation. Series compensation is to connect the capacitor directly to the high-voltage transmission line to improve transmission line parameters, reduce voltage loss, improve its transmission capacity, and reduce line loss. The capacitor of this compensation method is called a series capacitor, and is applied to a high-voltage long-distance transmission line, and the power unit is rarely used. Parallel compensation is to connect the capacitor directly to the same circuit on the compensated device to improve the power factor. The capacitor used in this compensation method is called a shunt capacitor, and the power company uses this compensation method. There are usually three ways to install the capacitors depending on where they are installed.

1. The centralized compensation capacitor group is installed in the 6~10kV busbar of the enterprise or local total step-down substation, which is used to improve the power factor of the whole substation, so that the reactive power in the power supply range of the substation is basically balance. It can reduce the reactive power loss of the high voltage line and improve the power supply voltage quality of the substation.

2. Group compensation The capacitor banks are respectively installed in the low-power workshop or the high-voltage or low-voltage busbar of the village terminal transformer substation, also called dispersion compensation. This approach has the same advantages as centralized compensation, with only the reactive compensation capacity and range being relatively small. However, the effect of group compensation is more obvious, and it is more common.

3. Local compensation The capacitor or capacitor assembly is placed near the asynchronous motor or inductive power equipment to perform reactive compensation on the spot, also known as individual compensation or individual compensation. This method can not only improve the power factor of the power supply circuit of the electrical equipment, but also improve the voltage quality of the electrical equipment, and is very suitable for medium and small equipment.