Power Factor

Concept of Power Factor

•Power factor is the factor upto which the power is actively used out of the total power 

generated. Meaning, the power generated is apparent power, out of which, the active 

usable power is apparent power times the power factor.

•The Power Factor (P.F.) is a ratio of the real power that is used to do work and the 

apparent power that is supplied to the circuit.

P. F. =kW/kVA

• The P.F. is widely known as the cosine angle between fundamental voltage and current.

•The P.F. is a dimensionless number in the closed interval of 0 to 1.

• Power factors are usually stated as "leading" or "lagging" to show the sign of the phase 

angle.

• The P.F. of 1 means that the voltage and current waveforms are in phase.

•When the power factor is 1, all the energy supplied by the source is consumed by the load.

• The P.F. of less than or greater than 1 means that the voltage and current waveforms are 

not in phase.

• Capacitive loads are leading (current leads voltage), and inductive loads are lagging 

(current lags voltage).

• Due to energy stored in the load and returned to the source, or due to a non-linear load 

that distorts the wave shape of the current drawn from the source.

Types of Power Factor

From the concept, power factor can be classified as following:

1) As per the supply consideration;

    •Displacement power factor 

    •True power factor

2) As per the nature of load consideration;

    •Unity power factor

    •Lagging power factor

    •Leading power factor

Displacement power factor

•Displacement power factor is the cosine of the angle between fundamental voltage and 

current waveforms. 

•The fundamental waveforms are by definition pure sinusoids. But if the waveform 

distortion is due to harmonics, the power factor angles are different than what would be 

for the fundamental wave alone.

•The presence of harmonics also affects overall power factor of the system.

True power factor or Distortion power factor

• True power factor is calculated as the ratio between the total active power used in a 

circuit (including harmonics) and the total apparent power (including harmonics) 

supplied from the source.

𝐓𝐫𝐮𝐞 𝐩𝐨𝐰𝐞𝐫 𝐟𝐚𝐜𝐭𝐨𝐫=𝐓𝐨𝐭𝐚𝐥 𝐚𝐜𝐭𝐢𝐯𝐞 𝐩𝐨𝐰𝐞𝐫/𝐓𝐨𝐭𝐚𝐥 𝐚𝐩𝐩𝐚𝐫𝐞𝐧𝐭 𝐩𝐨𝐰𝐞𝐫

• Utility penalties are based on the true power factor of a facility.

As shown in figure 6.1,

Unity power factor (for resistive load)

•If a purely resistive load is connected to a power supply, current and voltage will change 

polarity in step, the power factor will be unity (1), and the electrical energy flows in a 

single direction across the network in each cycle.

•When the power factor is 1, all the energy supplied by the source is consumed by the load.

•Unity power factor occurs in resistive type load.

•For pure resistive load, power factor angle becomes 0°.

Lagging power factor (for inductive load)

•If the resulting current phase angle is more negative in relation to the driving (source) 

voltage phase angle, then the power factor is said to be "lagging".

•Lagging power factor occurs in inductive type load.

•For pure inductive load, power factor angle becomes 90°.

Leading power factor (for capacitive load)

•If the resulting current phase angle is more positive in relation to the driving (source) 

voltage phase angle, then the power factor is said to be "leading".

•Leading power factor occurs in inductive type load.

•For pure capacitive load, power factor angle becomes -90°.

•The driving (source) voltage phase is often assumed to be zero (for convenience) and in 

that situation it is immediately obvious that a lagging power factor condition is indicated 

by a negative sign for the current phase angle. Similarly a positive sign for the current 

phase angle indicates a leading power factor.

Power Factor Correction

Two ways to improve the power factor and minimize the apparent power drawn from the 

power source are:

1) Reduce the lagging reactive current demand of the loads

2) Compensate for the lagging reactive current drawn by supplying leading 

reactive current to the power system

•Lagging reactive current represent the inductance of the power system and power system components. 

•Lagging reactive current demand may not be totally eliminated but may be reduced by 

using power system devices or components designed to operate with low reactive 

current requirements. 

•Practically no devices in a typical power system require leading reactive current to 

function; therefore, in order to produce leading currents certain devices must be inserted 

in a power system. 

•These devices are referred to as power factor correction equipment.

Advantages of power factor improvement

•Reduces reactive component of network

•Reduces total current in system from source to end 

•Reduces 𝐼2 𝑅 power losses 

•Increases Voltage level at load end (i.e. voltage drop is reduced)

•Reduces kVA loading on source generators 

•Reduces kVA loading on transformers 

•Reduces Line and cable loading 

•High P.F. can help in utilizing the full capacity of the electrical system

•Reduces heating in equipments

•Reduces energy losses and operating costs

•Increases equipment life 

Cost benefits of power factor improvement

•Reduces kVA charges (Maximum Demand charges) in utility billing

•Reduces distribution losses (kWh) within plant network.

•Improves voltage at motor terminals and performance of motors

•Eliminates penalty charges

•Reduces an investment on system facilities such as transformers, cables, switchgears etc.