kilowatts and kVARs

What is a kilowatt?  kW is the accepted measure of the real energy consumed by any process.  It is the product of volts and the

part of the total amps flowing that does real work, divided by 1000.  This current is called “real” current, and flows in phase

with the voltage.  This includes the “work” that produces heat in the cables and power delivery gear.

Describing “What is a kVAR?” is a little more difficult.  A kVAR is the accepted measure of reactive power, equal to the product

of the volts and the part of the current that is “reactive” divided by 1000.  Reactive current is the current that flows out of

phase with the supply voltage.  Reactive current supplying motors lags in time behind the voltage and the real current, as in A

below.  Reactive current that supplies capacitors leads in time ahead of the voltage and the real current, as in B below.  Lagging

reactive current magnetizes motors and transformers.

The real power (kW) and the reactive power (kVAR) are related like the legs of a right triangle as in the figure at the above

right. Each of the sides is shown as an arrow, called vectors. Since they are at right angles, they cannot simply be added together.

The longer vector (kVA) represents the total current (amperes) and the load on the system. The ratio [kW / kVA] of real power

(kW) to apparent Power (kVA) is called the power factor (pf).  The angle shown as A is the power factor angle.  If all kVAR were

eliminated, the apparent power (kVA) and real power (kW) would be equal and the power factor would be unit or 1.00.