In the AC circuit, 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.

有功功率是保持用電設備正常運行所需的電功率，也就是將電能轉換為其他形式能量(機械能、光能、熱能)的電功率。各種照明設備將電能轉換為光能，供人們生活和工作照明。

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). Various lighting devices convert electric energy into light energy for people's living and working lighting.

有功功率的符號用P表示，單位有瓦(W)、千瓦(kW)、兆瓦(MW)。

The symbol of active power is represented by P, and the units are watt (W), kilowatt (kw) and megawatt (MW).

無功功率比較抽象，它是用于電路內電場與磁場的交換，并用來在電氣設備中建立和維持磁場的電功率。它不對外作功，而是轉變?yōu)槠渌问降哪芰俊７彩怯须姶啪€圈的電氣設備，要建立磁場，就要消耗無功功率。由于它不對外做功，才被稱之為“無功”。無功功率的符號用Q表示，單位為乏(Var)或千乏(kVar)。

Reactive power is more abstract. It is used for the exchange of electric field and magnetic field in the 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. All electrical equipment with electromagnetic coils must consume reactive power in order to establish a magnetic field. Because it does not work externally, it is called "reactive power". The symbol of reactive power is represented by Q, and the unit is var or kvar.

無功功率決不是無用功率，它的用處很大。電動機需要建立和維持旋轉磁場，使轉子轉動，從而帶動機械運動，電動機的轉子磁場就是靠從電源取得無功功率建立的。變壓器也同樣需要無功功率，才能使變壓器的一次線圈產生磁場，在二次線圈感應出電壓。因此，沒有無功功率，電動機就不會轉動，變壓器也不能變壓，交流接觸器不會吸合。

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.

在正常情況下，用電設備不但要從電源取得有功功率，同時還需要從電源取得無功功率。如果電網中的無功功率供不應求，用電設備就沒有足夠的無功功率來建立正常的電磁場，那么，這些用電設備就不能維持在額定情況下工作，用電設備的端電壓就要下降，從而影響用電設備的正常運行。無功功率對供、用電產生一定的不良影響，主要表現在：

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 the rated condition, and the terminal voltage of the electrical equipment will drop, thus affecting the normal operation of the electrical equipment. Reactive power has certain adverse effects on power supply and consumption, mainly in the following aspects:

1、降低發(fā)電機有功功率的輸出。

1. Reduce the output of generator active power.

2、降低輸、變電設備的供電能力。

2. Reduce the power supply capacity of power transmission and transformation equipment.

3、造成線路電壓損失增大和電能損耗的增加。

3. It causes the increase of line voltage loss and electric energy loss.

4、造成低功率因數運行和電壓下降，使電氣設備容量得不到充分發(fā)揮。

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

從發(fā)電機和高壓輸電線供給的無功功率，遠遠滿足不了負荷的需要，所以在電網中要設置一些無功補償裝置來補充無功功率，以保證用戶對無功功率的需要，這樣用電設備才能在額定電壓下工作。這就是電網需要裝設無功補償裝置的道理。

The reactive power supplied from the generator and high-voltage transmission line is far from meeting the needs of the load. Therefore, some reactive power compensation devices should be set in the power grid to supplement the reactive power, so as to ensure the needs of users for reactive power, so that the electrical equipment can work under the rated voltage. This is why the power grid needs to be equipped with reactive power compensation devices.

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