Difference Between VA and Watts
VA vs Watts
“VA,” the abbreviation of volt-amperes, and watts are two units that are used to measure power. The main difference between VA and watts is what kind of current they are. Watts is the unit used for real power while VA is used for apparent power. Real power, or watts, is the power that is actually consumed by the resistive loads. All components have some amount of resistance so each part consumes an amount of real power. Apparent power, or VA, is real power combined with the effects of reactive loads like capacitors and inductors.
Regardless of whether you are using AC or DC, the watts would still be the same as resistive loads act in the same exact manner with either supply. Reactive loads do not behave in the same way. Capacitors act as open circuits while inductors act as short circuits when under DC. But in AC, they add a complex component to the power. The complex component, combined with the real part (watts), results in the apparent power (VA). Under DC, watts and VA are equal as there is no complex component.
There is a reason why we need to distinguish between VA and watts and it is efficiency. Watts is the actual power needed to accomplish the job in AC, but the power consumed is the much higher VA. In order to minimize the wasted power, it is necessary to get the VA value as close as possible to the watts value. The ratio between the two is the power factor, and it is desirable to get a power factor of “1” or close to it in order to achieve maximum efficiency. This is achieved through power factor correction. This is the addition of capacitive or inductive components depending on whether the circuit has too much inductance or too much capacitance. This is often done by large companies that operate heavy machinery as their power consumption is large enough that the power factor correction can significantly decrease their power needs.
Summary:
1.VA is the apparent power while watts is the real power.
2.VA is always greater than or equal to watts.
3.VA only applies for AC while watts applies for both AC and DC.
4.VA is the power consumed by the device while watts is the work it does.
5.The ratio between the VA and the watts is the power factor.
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Efficiency varies by a small amount with power factor. This article states that all of the difference between the VA and the watts of a load are accounted as reduced efficiency, which means losses. This is not correct. Efficiency accounts for watts that are lost by heating, noise, and other effects. The reactive power that is the difference between watts and VA primarily go into energizing electromagnets. In a motor, for example, the windings of the motor form an electromagnet and the reactive power magnetizes the windings, which then allow the watts to be transferred to the shaft so that work may be accomplished. Efficiency should be left out of this article as it is not directly relevant to the topic.