power factor

What is Power Factor?

Power factor is defined as the cosine angle between voltage and current in an alternating current (AC) circuit. Unlike in DC circuits, a phase angle difference, ϕ exists between voltage and currents in an AC circuit. The cosine of ϕ (or Cos ϕ) is termed as the power factor.

1.REACTIVE CIRCUIT (UNITY POWERFACTOR)

2.INDUCTIVE CIRCUIT (LOGGING POWERFACTOR)

3.CAPACITIVE CIRCUIT (LEADING POWER FACTOR)

If the circuit consists of inductive elements or it behaves like an inductive circuit (where current lag behind the voltage), then the power factor in that circuit is referred as a lagging power factor.

On the other hand, if the circuit is capacitive in nature where current leads the voltage, then the power factor is referred as the leading power factor. If there is no phase angle difference between the voltage and current then it is unity power factor.

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Consider above waveforms and phasor diagram of an inductive circuit where current lags the voltage by an angle ϕ. Here, the total current is resolved into two components.

The I cos ϕ component is called wattful  or active component and it is in phase with the source voltage. The I sin ϕ component is called wattless or reactive component and it is 90⁰ out of phase with the source voltage.

From the figure we can say that the angle from these two components decides the power factor, and it implies that if the reactive component is small, the phase angle ϕ is small resulting high power factor (In every electric circuit, power factor should be maintained high for a better utilization of power). Thus, a small reactive current in the circuit results a high power factor and vice-versa.

It is to be noted that the power factor can never be more than unity. The most efficient loading of the supply results a power factor of 1. Suppose, if the power factor of the load is 0.8 means there are much higher losses in the supply system.

Generally power factor is indicated with words lagging and leading, in addition to the value. This is to represent whether current leads or lags by the voltage. For example, 0.8 lagging implies that the circuit has a power factor of 0.8 where current lags the voltage. Sometimes, it is also indicated as a percentage such as 80% lagging.

Power factor can also be expressed in terms of power consumed by electrical equipment or a complete electrical installation. In such case power factor is defined as the ratio between the true power (KW) to the total apparent power (KVA).

Consider the above power triangle which gives the relation between various powers. The VI cos ϕ, component is called true or active power which is measured in watts (W) or Kilowatts (KW). It causes useful work in the circuit.

he VI sin ϕ, component is called wattles or reactive power and it is measured in volt-amperes-reactive (VAr) or kilo-volt-amperes-reactive (kVAr). It is caused by inductance or capacitance in the circuit and it does two main functions; to provide magnetic field and to charge capacitors.

The resultant component of true and reactive or simply a VI component is called apparent power and it is measured in volt-amperes (VA) or kilo-volt-amperes (kVA).

From the figure, power factor, cos ϕ = active power/ apparent power = VI cos ϕ/ VI

cos ϕ = KW/KVA

The above expression of power factor measures how efficiently electric power is converted into useful work output. And also, from the power triangle, reactive power component measures the power factor. If the reactive power component is small, the power factor will be high and vice-versa.