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Introduction to active power and reactive power

   Active power is to maintain the normal operation of the electric equipment to the electric power, which is the electric energy conversion to other forms of energy (mechanical energy, light energy, heat) power. Such as motor 5.5 kW is to 5.5 kilowatts of electrical energy conversion into mechanical energy, driven pump or threshing machine; a variety of lighting equipment will be conversion of electric energy into light energy for people living and working lighting. The symbol of active power is expressed in P, the unit has a Watts (W), kW (kW), MW (MW).

   Reactive power is abstract, it is used in the electric field and magnetic field in the circuit, and used in electrical equipment to establish and maintain the electric power of the magnetic field. It does not work, but is transformed into other forms of energy. All electrical equipment with the electromagnetic coil, to establish a magnetic field, we must consume reactive power. For example, 40 Watt fluorescent lamp, in addition to 40 watts active power (ballast also need to consume a certain amount of active power) to shine outside need 80 spent around without power for ballast coil set up with alternating magnetic field. It is not because of external work, is called "reactive power". Reactive power symbol with Q said, the unit is deficient (Var) or kilovar (kVar).

   Reactive power is not useless, it's very useful. Motor need to establish and maintain the rotating magnetic field, so that the rotor rotation, so as to drive the mechanical movement, the rotor magnetic field of the motor is obtained from the power supply of the power to establish the. Transformer is also required to make the power of the transformer, the transformer is a coil to generate a magnetic field, in the two coil induced voltage. Therefore, no reactive power, the motor does not rotate, transformer cannot swing, AC contactor will not. To vividly illustrate the problem, we give an example: rural water need to repair the excavation soil, soil with bamboo basket filled with soil, picked the soil like active power, pick an empty bamboo basket is like a reactive power, the bamboo basket is not used, no bamboo basket of earth how to transport to the bank?

   Under normal circumstances, the use of electrical equipment not only to obtain active power from the power, but also from the power to achieve reactive power. If there is no shortage of reactive power in the power grid, power equipment is not enough to establish the normal electromagnetic field, then, these devices can not be maintained at the rated condition, with the power of the device is to be reduced, affecting the normal operation of electric equipment. Reactive power supply, power generation of a certain adverse effects, the main performance in:

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

  (2) reducing the power supply capacity of the transmission and substation equipment.

  (3) the increase of the voltage loss and the power loss of the line.

  (4) cause low power factor operation and voltage drop, so that the capacity of electrical equipment can not be fully played.

  The active power can be measured directly; the active and reactive power can not be separated directly from the power factor.

Keywords:Active power filter,Active filter, Power quality,Harmonic control,APF
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