Difference between KW,KVA and KVAR

Difference between kW, kVA and kVAR

The units are of the same “size”, but are used for different properties of the feed:

kW – Real Power
kVA – Apparent Power
kvar – Reactive Power

The relationship between the three values can be summarized in the following figure:

The real power and the reactive power together (root of the sum of the squares) give you the apparent power. On your bill, if you are on a demand tariff, you will be billed for the apparent power (kVA). The power factor determines how close the apparent power is to the real power (a PF of 1 would have the apparent power = real power). 

KW is Working Power (also called Actual Power or Active Power or Real Power).

It is the power that actually powers the equipment and performs useful

work.

KVAR is Reactive Power.

It is the power that magnetic equipment (transformer, motor and relay)

needs to produce the magnetizing flux.

KVA is Apparent Power.

It is the “vectorial summation” of KVAR and KW.

Power Factor (P.F.) is the ratio of Working Power to Apparent Power.

Looking at our beer mug analogy above, power factor would be the ratio

of beer (KW) to beer plus foam (KVA).

P.F. = KW

KW + KVAR

. = Beer

Beer + Foam

Great. I now understand what power factor is. But I’ve been told mine is low.

What did I do to cause this?

Since power factor is defined as the ratio of KW to KVA, we see that low power

factor results when KW is small in relation to KVA. Remembering our beer mug

analogy, this would occur when KVAR (foam, or Mac’s shoulder height) is large.

What causes a large KVAR in a system? The answer is…inductive loads.

Inductive loads (which are sources of Reactive Power) include:

􀂉 Transformers

􀂉 Induction motors

􀂉 Induction generators (wind mill generators)

􀂉 High intensity discharge (HID) lighting

These inductive loads constitute a major portion of the power consumed in

industrial complexes.

Reactive power (KVAR) required by inductive loads increases the amount of

apparent power (KVA) in your distribution system (Figure 4). This increase in reactive

and apparent power results in a larger angle θ (measured between KW and KVA). Recall

that, as θ increases, cosine θ (or power factor) decreases.

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