Types of Power and Power Factor

In the power system, three quantities are most important;

  1. Voltage
  2. Current
  3. Frequency

Power quality is an important concern in the power system because it affects the voltage, current, and frequency. The power factor is an important aspect of improving the power quality of supply.

A load with a unity power factor has good efficiency and it can save a considerable amount of cost. For, this reason, the majority of utility companies demand the reduction of reactive power. If reactive power demand decrease, the power factor will improve.

Types of Power

There are three types of power;

  1. Apparent power
  2. Active power
  3. Reactive power
power triangle
power triangle

1) Apparent Power

The apparent power denoted as ‘S’. It is the product of the RMS voltage and current. Volt-amperes or VA is a unit of the apparent power.

S = V X I (for single phase apparent power)

S = 1.73 V X I (for three phase apparent power)

Where V is phase voltage and I is line current

 S = P + jQ

|S|2 = P2 + Q2

The power factor is a ratio of real power (P) to the apparent power (S).

2) Active Power

The active power is also known as true power or real power. This power is a useful power for the load. The unit of the active power is WATT (W) and denoted as P.

WATT is a very small unit, so power measured in kW or MW. The active power carried out in the power system by the part of the current. This current is always in phase with the supply voltage. The real work cannot be done when the current is out of phase with the supply voltage.

Active power P = VI cosθ (kW)

3) Reactive Power

The reactive power is a part of an apparent power which is out phase with the real power. This is happening in the power system by reactive elements like inductors and capacitors.

This power does not use for the load. The reactive power is also known as the imaginary power. The unit of reactive power is volt-ampere-reactive (VAR).

Reactive Power Q = VI sinθ (kVA)

Power Factor

The power factor is the ratio of active power (true power) to the power supplied by the power system (apparent power).


PF = P/S

In a power triangle, θ is the angle between current and voltage. The power factor defined as the cosine angle between the phase voltage and the line current.

PF = cosθ

The power factor is a dimensionless quantity. The range of power factor is between -1 to 1. In an ideal power system, the power factor is unity (1), which means that there is only real power is available.

There is an absence of reactive power. But in the actual power system, we can not ignore the reactive power and it always is present in the power system. So, in the actual power system, the power system cannot unity, but for good quality of supply, we try to maintain the power factor near to the unity.

In the power system, we use FACTS devices to improve the power factor.

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