How to improve power factor ?
Power factor has been defined earlier as a function of active and apparent power. For sinusoidal (undistorted) voltage and current, a vector representation is also possible and helpful.
For most electrical loads like motors, the current I is lagging behind the voltage V by an angle phi.
Ia is called the “active” component of the current.
Ir is called the “reactive” component of the current.
The above diagram drawn up for currents also applies to powers, by multiplying each current by the common voltage V.
We thus define:
- Apparent power: S = V x l (kVA)
- Active power: P = V x la = V x I x cos phi (kW)
- Reactive power: Q = V x lr = V x I x sin phi (kvar)
The physical unit for the reactive power is one volt-ampere-reactive (var), with one kilovolt-ampere-reactive (kvar) often used for commodity.
Thus, the supply source has to provide not only the active power P, but also the reactive power Q, resulting in the apparent power S.
It can be easily seen from figure above that for a given active power P, there is a great benefit to decrease the phase angle phi, so that the apparent power and the corresponding current could be reduced.
The principle of “Power Factor Correction” (or “Reactive Energy Compensation”) is to generate the reactive power close to the load, so that the supply source could be relieved. Capacitors are most commonly used to supply reactive energy to inductive loads such as motors.
Qc is the reactive power produced by the capacitors. S’ is the apparent power after compensation.
Capacitor bank s can be arranged to provide a fixed value of reactive energy or variable values by steps.
For highly fluctuating loads such as lifts, crushers …, electronic compensators have been designed in order to provide fast and continuously varying compensation.