Power Factor

In an AC power system, the power factor plays a very major role which defines how efficiently electrical power is being utilized by load. Power factor of a system depends on the type of load. Example : Resistive, inductive or capacitive. Poor power factor in the system results in increase in the current drained by the load.

Power Factor 

Power Factor is the ratio of real power (Active power) to apparent power and also defined as the cosine of the phase shift between the voltage and current in an AC circuit. 

$Power Factor \left(\lambda \right) = \frac{Active Powe\mathrm{r\; / }}{Apparent Power}$

$\; \; \; \; \; \; \; \; \; \; \; \; \; \; = \frac{VI.\cos \left(\mathrm{\varphi \; / }\right)}{VI}$

$\; \; \; \; \; \; \; \; \; \; \; \; \; \; = \cos \left(\varphi \right)$

Where

V - Voltage in Volts

I - Current in Amperes

Ⲫ - Phase angle between voltage and current

POWER FACTOR

Active Power (KW)

It is the True power transmitted to the load for Energy Conversion. Ex: A motor consumes the true power from the circuit and converts it into mechanical power. It is denoted by the symbol P.

Reactive Power (KVAR)

Reactive Power is the power required to produce the magnetic field in motors has a direct impact on the P.f. It is denoted by the letter Q. 

Apparent Power (KVA)

Apparent Power is the product of voltage and current consumed by a load irrespective of its phase angle. It is denoted by the letter S.

Leading Power Factor

In case of capacitive load, Current leads the voltage (i.e.) apparent power leads the real power. It is considered as the leading power factor.

Lagging Power Factor

In case of inductive load, Current lags the voltage (i.e.) apparent power lags the real power. It is considered as the lagging power factor.

Unity Power Factor

In case of resistive load, the current flow to the load will be linear and the phase angle difference between the voltage and current will be zero. so that the power factor cos Ⲫ is O.

Disadvantages of Poor Power Factor

• If the power factor is low, it draws more current irrespective of its power capacity. Hence, this increases the size of the cable which we going to use.
• High current flow cause high copper loss
• Poor Voltage regulation in transformers, alternators and transmission lines

Causes of Low power Factor

High Inductive loads are major cause for lower power factor. Its power factor may vary from 0.4 at starting to 0.8 or 0.9 at full load. Example : Induction motors, Induction heating furnaces, Arc lamps have very poor power factor.

Power Factor Correction

In order to overcome lagging power factor due to inductive power loads, we have to neutralize the lagging current by adding leading current. 

• Connecting Synchronous compensators - Synchronous motors runs at no load. It act as a capacitor and supplies reactive power to the system.
• Adding static capacitors - capacitors should be connected in parallel to inductive loads. in this, contactors used for switching and connecting capacitor to the system based on the requirement.
• Adding VAR compensators - Thyristors are used for Switching instead of contactors