# Power Factor Correction Methods

Before studying the power factor correction methods, it is important to understand the causes of low power factor. Moreover, if you want to study about the power factor, kindly read the following article :

What is Power Factor ?

Power factor is defined as the ratio of active (real) power to apparent power. Apparent power (KVA) is a combination of both active (KW) and reactive power (kVAR). Lets write the power factor formula to understand in more clear way. Or we can write as :

###### …..     (2)

From eq.(2), we can say that the reactive power ( kVAR ) component decides the value of power factor. Greater the value of reactive power component, lower is the power factor of the circuit and vice versa. The main reason for the low power factor is that most of the power loads are inductive in nature. Inductive load takes reactive power from the source which  results in low power factor. The main causes of the low power factor is as follows:

Induction Motor:

Most of the AC motors like induction motor ↗ (both single phase and three phase) are inductive in nature. In case of inductive load, current lags the voltage. The large phase angle difference between current and voltage results in low lagging power factor. Induction motor has a very poor power factor at small loads usually range from 0.2-0.3. At full load, power factor rises a little above and have a value from o.8-o.9. Hence inductive loads are the main cause of low power factor.

Transformer:

Transformers are also responsible for having a low power factor since they draw the magnetizing current which flows in the primary windings of transformer. This current doesn’t affect the power factor at normal load. However, during the time of low load period ,transformer draws large amount of magnetizing current which results in low lagging power factor.

Electric discharge lamps:

Electric discharge lamps, Arc lamps and industrial heating furnaces also operates at low lagging power factor.

##### Power factor Correction Methods:

The main reason for low power factor is due to the fact that most of the power loads are inductive in nature and take lagging currents. In order to improve power factor, devices taking leading current are generally connected in parallel with the load which raises the power factor of the load. Following are some of the power factor equipment which are generally used to improve the power factor.

Power Factor improvement using Capacitor bank:

Power factor can be improved by installing capacitor in parallel with the load operating at lagging power factor. Capacitor draws a leading current (i.e. current waveform leads the voltage) and neutralizes the lagging reactive component of the load current by supplying the reactive power. In that case, load will only draw the active power from the source due to which power factor of the equipment gets improved. In case of three phase loads, capacitors can be connected in delta or star as you can see in the fig. Moreover, capacitor can be easily installed and have low losses. Synchronous Condenser:

Synchronous motor draws leading current when it is over excited↗. An over excited synchronous motor running on no load is known as synchronous condenser. In order to improve the power factor, synchronous condenser is connected in parallel with the inductive load. In that case, the entire reactive component of the current is supplied by the synchronous condenser due to which power factor of the load gets improved. The main reason for having a low power factor in induction motor is due to its stator windings which draws a lagging excited current from the supply. If the exciting current is provided by other source, power factor of the motor gets improved.

Phase advancer is an AC exciter used for the power factor correction of induction motors. It is mounted on the shaft of induction motor and provides the extra ampere turns to the rotor in order to produce the required air gap flux. In case of increasing the excitation current, induction motor can be made to operate at leading power factor.

Why it is important to improve power factor?

Since most of the electrical loads in any power system are inductive in nature. This simply means that the load will draw the reactive component of current from the source. The large currents at low lagging power factor causes excessive voltage drop in alternators, transformers and in the transmission lines. That’s why it is important to improve power factor.

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