本文是其中的一部分能源管理系列：What’s the Difference Between Watts, RMS, and More?
Both watts (W) and volt-amperes (VA) are units of measurement for electrical power. Watts refer to “real power,” while volt-amperes refer to “apparent power.” Usually, electronic products show one or both of these values to provide information about how much energy they will consume or how much current they will draw. Each of these values can be used for various purposes.
什么是瓦特？
瓦特的实力是执行工作或产生热量的功率。瓦特的电力是消耗能量（或生成）的速率。一个瓦特是每秒一个焦耳（能量）（1 w = 1 j / s）。您将您的公用事业公司支付为表达为能源的瓦，这是一段时间段的电力，通常由您的公用事业公司在千瓦时显示。例如，100W电灯泡留在10小时内，消耗1千瓦小时的能量（100W×10小时= 1000W-ops = 1 kW-小时）。
DC电路的实际电源只是电压（V.DC.）当前的次数（我DC.):
W = VDC.X I.DC.(1)
计算AC电路的实际功率的概念是简单的，但是执行计算得多难度。为了获得瓦特的力量，您需要使用时间，v（t）和带时间的瞬时电流来了解瞬时电压，i（t）。当您将这些乘以时，您可以随时获得瞬时功率，p（t）。
由于这种瞬时电源随着时间的推移而变化，因此我们需要获得平均值，因此我们在一段时间内集成了电力并将电力分开并在时间段划分以获得平均值。这使我们通过在电压V（t）的电路中，通过它和电流i（t）通过它来使设备在电压V（t）中散发的瓦特在评估的时间段内。假设电压和电流既是周期性的周期性波形，则表示期间T周期性波形的功率计算的严格数学方式是：
因此，虽然这可能很容易想象，但计算不易计算。甚至对AC电路的瓦特的实际功率的测量也需要专门的设备（瓦特计），因为必须在精确的时间段内测量电压和电流波形，测量必须是同时的，并且必须在测量时间上计算平均值时期。标准万用表无法进行此类功率测量。
什么是瓦特用于？
These ratings are useful if you have to get rid of the heat generated by the device consuming the watts or if you want to know how much you will pay your utility company to use your device since you pay for kilowatt-hours (power used for a period of time). To combine the real power of multiple dc or ac devices, you can just add up the individual power ratings in watts of each device to get the total power (watts add linearly).
什么是伏安？
The apparent power in VA is used to simplify power ratings, making it easier to calculate current draw. Since VA = RMS volts x RMS amps, you can divide the VA rating by your RMS voltage to get the RMS current the device will draw. Knowing the RMS current helps you properly size wires and circuit breakers or fuses that supply current to your device.
如何计算伏安？
The apparent power for dc circuits is simply the voltage (VDC.）当前的次数（我DC.):
VA = VDC.X I.DC.（3）
The apparent power for dc circuits is the same as real power for dc circuits (for dc, VA = W).
For ac circuits, VA are the product of the RMS voltage (Vrms.) times the RMS current (Irms.):
VA = Vrms.X I.rms.（4）
您可以通过将测量的RMS电压乘以测量的RMS电流来计算AC电路的Volt-yperes的表观电力。标准万用表通常可以使这两个RMS测量值。
什么是伏特 - 安培用于？
Volt-amperes provide insight into the amount of current drawn by a product or circuit, assuming you know the voltage. For example, the standard residential voltage in the United States is 120 Vrms.。如果产品被评定为300 VA（评级意味着这是产品的最大VA）并由120 V.rms.交流线电压，可以计算预期的最大电流为300 VA / 120 V.rms.= 2.5 A.rms.最大（见图）。因此，您希望确保提供该产品的电线和相关电路容纳至少2.5 arms.。
To combine the apparent power of multiple dc devices, volt-amperes add linearly. However, to combine the apparent power (or current) of multiple ac devices, there is no straightforward way to get an exact total because the currents for each device are not necessarily in phase with each other, so they don’t add linearly. But if you do simply add the individual VA ratings (or currents) together, the total will be a conservative estimate to use since the actual total will always be less than or equal to this value.
Another term that is useful in this discussion is power factor (PF). The power factor is defined as the ratio of W to VA:
力量factor = PF = W/VA (5)
力量factor is always a number between zero and one because the watts drawn by a device are always less than or equal to the volt-amperes. Note that it is possible for a circuit to have a large voltage across it and to draw substantial current, but consume no energy (dissipate zero watts).
虽然这似乎是违反直观的，但如果电路纯粹反应性（纯电容器或纯电感器），则是真的。电路将无效并产生没有热量，因此它是绘制（和耗散）零瓦特。然而，它可以汲取大量的电流，导致大量的VA。
In this case, the power factor is zero. This is possible because the phase relationship between the voltage and current waveforms is such that the circuit is alternately absorbing real power and giving that real power back, so the net real power consumption is zero.
概括
W和VA都是电力测量单位，但这就是相似性结束的地方。瓦特确实工作或产生热量，而Volt-yperes只需为您提供尺寸电线，保险丝或断路器所需的信息。瓦特加入线性，而伏安否则没有。并测量W，您需要一个特殊的瓦特计。您可以使用标准万用表来计算VA来测量vrms.和我rms.and finding the product（见表）。
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