KVW vs KVA
Look at any electrical machine and you’ll find a power rating. This is usually shown as kilowatts (kW), but sometimes you’ll see a kVA, or kilovolt-ampere rating. Although both ratings express power, they are different.
Kilowatts. A kilowatt is the real or actual power that the machine provides: Voltage x Current. This is the amount of power that a machine can provide based on its horsepower.
Kilovolt Amperes. A kilowatt ampere is the “apparent” power provided by the machine. It will always be higher than the kW rating, but only a portion of the kVA is available to do the work. In direct-current (DC) situations the kW and kVA are the same because the voltage and the current do not get out of phase. In alternating current (AC) situations, this is not the case. In AC systems, the voltage and current can get out of phase with one another. In that case the kW rating tells you how much actual power is available, the kVa indicates an excess of the current.
In other words, the kVA is the amount of current a device can draw in while the kW is the amount of power the device puts out.
The Power Factor
The difference between the kilowatt rating and the kilovolt-ampere rating is something called the Power Factor. The power factor is a value that varies with every electrical device or machine, somewhere between 0 and 1. The value is expressed with a percentage with 100% representing unity of current. With unity, there is no difference between the kW and the kVA. The closer to 100% that machine rates, the more efficiently it uses electricity, which is where it becomes important when evaluating generators.
Why kVA Matters
While the U.S. most commonly uses kW to express power ratings, most of the rest of the world uses kVA. Although the kilovolt-ampere may seem like extraneous data, it really isn’t. You need to know the kVA to ensure your facility has the proper wiring capabilities to carry this extra current, even though the machine won’t be using it. Generators also carry the kVA rating so you can determine if it will be able to handle the extra current for reactive loads.
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