Electrical job question: What is Power Factor ?

Types of Current:

There are two types of currents present in the AC circuits.

The current required by induction motors, transformers, fluorescent lights, induction heating furnaces, resistance welders, etc., may be considered to be made up of two separate kinds of current: magnetizing current and power-producing current.

Power-producing current:

This is also called working current  is that current which is converted by the equipment into useful work such as lighting a fluorescent light, making a weld, or pumping water. Hence the power required to perform a useful job or real work is termed as Active Power. The unit of measurement of the power produced is the kilowatt (kw).

Magnetizing current:

This type of current is also known as wattless, reactive, or non-working current. It is the current which is required to produce the flux necessary to the operation of induction devices. Without magnetizing current, energy (Active Power) could not flow through the core of a transformer or across the air gap of an induction motor. The unit of measurement of magnetizing volt-amperes is the kilovolt-ampere-reactive (kvar).

But the current that is read on an ammeter in the circuit is Total Current which include both magnetizing current and power producing current . Most a-c power systems require both kilowatts and kilovars. Power required to perform certain operation ( say running of induction motor) requires both active component of the power and magnetizing  or reactive component of the power. This total power is coined as "apparent power" having  the unit of measurement of  kilovolt-ampere (kva).

In simple,

Active power:

Power required to do the useful work (kW)

Reactive Power:

Power required to magnetizing effect ( flux required)  the ac circuit and is important to deliver the active power in the circuit. ( kvar)

Apparent Power:

Power combining both active power and reactive power.(kva)

 Power factor:

• Power factor of a circuit may be expressed as the ratio of power-producing current in a circuit to the total current in that circuit.
• Another definition of power factor, which is generally more useful, is the ratio of kw or working power to the total kva or apparent power.

Thus, Power Factor=Active Power/Apparent Power

Some of the causes of low power factor and methods to improve power factor are already discussed