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How to understand the active power and reactive power?

Date: 2018-03-19 15:53:10 Click:

The device converts electric energy to light energy for people's life and work lighting. The symbol of active power is expressed by P. The unit has watts (W), kilowatts (kW) and megawatts (MW).

Reactive power is more abstract. It is used to exchange electric field and magnetic field in electric circuit, and is used to establish and maintain the electric power of magnetic field in electrical equipment. It does not work externally, but is transformed into other forms of energy. For any electrical equipment with electromagnetic coil, it is necessary to consume reactive power to establish magnetic field. Because it does not work outside, it is called "reactive power". Reactive power symbol with Q said, the unit is deficient (Var) or kilovar (kVar).

Reactive power is by no means useless power, it is of great use. The motor needs to establish and maintain the rotating magnetic field to turn the rotor and drive the mechanical motion. The rotor magnetic field of the motor depends on the reactive power obtained from the power supply. The transformer also needs reactive power to generate a magnetic field at the primary coil of the transformer and to induce the voltage in the two coil. Therefore, without reactive power, the motor will not rotate and the transformer will not change voltage, so the AC contactor will not suck.

Under normal circumstances, the electrical equipment not only obtains active power from the power, but also needs reactive power from the power supply. If the power of reactive power in the power grid is in short supply, there is not enough reactive power to establish normal electromagnetic field, then the equipment can not work under the rated condition, and the end voltage of the electrical equipment will be reduced, which will affect the normal operation of the electric equipment. Reactive power has some adverse effects on power supply and electricity consumption.

1, reduce the output of the active power of the generator.

2, reduce power supply capacity of transmission and substation equipment.

3, cause the increase of line voltage loss and the increase of electric energy loss.

4, cause low power factor operation and voltage drop, so that the capacity of electrical equipment can not be brought into full play.

The reactive power supplied from the generator and the high voltage transmission line can not meet the needs of the load, so some reactive power compensation devices should be set up to supplement the reactive power in order to ensure the needs of the reactive power of the users, so that the electric equipment can work at the rated voltage. That's the reason why the power grid needs to install reactive power compensation devices.