在电气设备的标牌上经常会看到额定容量 KVA、有功功率KW等技术参数，除此之外，还有无功功率、视在功率，那么什么事有功功率。

有功功率，但从字面意思看不出什么道道，但是有功功率的英语原意是Active Power，看到Active是不是已下载就明白“有功”的意思了。

1 英语愿意

有功功率：Active Power / Real Power

2 英文解释

2.1 Active 单词解释

1) active adjective (BUSY)

busy with a particular activity

忙于…的

例句：

physically/mentally active经常运动的／思想活跃的You have to try to keep active as you grow older.年岁大了，应该尽量保持身心活跃。

2) active adjective (INVOLVED)

involved in a particular activity

参与…的

例句：

Enemy forces remain active in the mountainous areas around the city.敌军在城市周围的山区仍然活动猖獗。She's very active in (= involved in) local politics.她积极参与当地的政治活动。He takes a more active role in the team nowadays.现在他在队里发挥着更为积极的作用。She's an active member of her trade union (= not only belongs to it, but does work to help it).她是工会中的活跃分子。

2.2 What Is Active Power?

Active power is often called real, actual, true, or useful power. In DC circuits, power is simply the voltage across the load times current flowing through it because in DC circuits there is no phase angle between the voltage and current therefore no power factor in DC circuits. In other words, the voltage and current are in phase with each other, meaning the voltage and current start at the same time, reach a peak, and then again touch zero at the same time.有功功率通常称为真实功率、实际功率、真实功率或有用功率。在直流电路中，功率只是负载两端的电压乘以流过它的电流，因为在直流电路中，电压和电流之间没有相位角，因此直流电路中没有功率因数。换句话说，电压和电流是同相的，这意味着电压和电流同时开始，达到峰值，然后再次同时触及零。

P=V × I for DC circuits

Whereas in AC circuits, there is a phase angle between voltage and current expressed with the added component of cosθ. 而在交流电路中，电压和电流之间存在相位角，用 cosθ 表示。

In a single-phase AC circuit active power is:

P=V × I × cosθ

In a 3-phase AC circuit:

P=√3 × V × I × cosθ

In Figure below, the current and voltage are in phase with each other making a +90 degree angle at the same time and the positive voltage times positive current generates positive power. When both current and voltage are negative, the power is still positive therefore in both cases the power is always positive this is called active power. The power curve will lie entirely above the horizontal axis and reflects that all of the work done is positive. 在下图中，电流和电压同时同相，形成+90度角，正电压乘以正电流产生正功率。当电流和电压均为负时，功率仍为正，因此在这两种情况下，功率始终为正，这称为有功功率。功率曲线将完全位于水平轴上方，并反映出所做的所有工作都是正的。

Current and voltage are in phase with each other

Features of Active Power 有功功率的特性:

The active power is always positive and does not change its direction, always flows from source to load. 有功功率始终为正，不会改变其方向，始终从源头流向负载。

Denoted by P and measured in watts (kW, MW, GW). 用 P 表示，以瓦特（kW、MW、GW）为单位。

Measure using a wattmeter. 使用瓦特计进行测量。

Active power produces heat, mechanical power, and light. 有功功率产生热量、机械动力和光。

3 中文解释

有功功率，是指单位时间内实际发出或消耗的交流电能量，是周期内的平均功率。单相电路中等于电压有效值、电流有效值和功率因数的乘积。多相电路中等于相数乘以每相的有功功率。单位为瓦、千瓦。

4 功率三角形

KW、KVar和KVA之间的关系可以用一个功率三角形来表示，它是一个直角三角形，两直角边分别为Q与P，斜边为S，S与P之间的夹角Ф为功率因数角，它反映了该交流电路中电压与电流之间的相位差（角）。

根据公式可以看出它们之间的关系就是：S²=P²+Q²

5 感悟体会

明明是激活的意思，为什么翻译成“有功”啊，专业术语一翻译，大部分信息都丢失了，还是真英文原文更好理解啊。