Electrical Engineering ⇒ Topic : Disadvantages of Low Power Factor

Disadvantages of Low Power Factor

The power factor plays an important role in a.c. circuits since power consumed depends upon this factor. The greater the power factor (i. e. closer to 1) of the load, the larger the active power delivered to the load

It is clear from above that for fixed power and voltage, the load current is inversely proportional to the power factor. Smaller the power factor, higher is the load current and vice-versa. The large current due to poor power factor results in the following disadvantages

(1) Large kVA rating of equipment. The electrical machinery (e.g., alternators, transformers, switchgear etc.) is always rated in **kVA.

It is clear that kVA rating of the equipment is inversely proportional to power factor. The smaller the power factor, the larger is the kVA rating. Therefore, at low power factor, the kVA rating of the equipment has to be made more, making the equipment larger and expensive.

(2) Greater conductor size. To transmit or distribute a given amount of power at constant voltage, the conductor will have to carry more current at low power factor. This necessitates large conductor size.

(3) Large copper losses. The large current at low power factor causes more I2R losses in all elements of power supply. This results in poor efficiency.

(4)Poor voltage regulation. The large current at low lagging power factor causes greater voltage drops in alternators, transformers, transmission lines and distributors. This results in the reduced voltage available to the utilisation devices, impairing their performance e.g. lighting becomes dimmer, starting torque of motors is reduced etc. In order to keep the supply voltage within permissible limits, extra equipment (i. e. voltage regulators) is required.

(5)Reduced handling capacity of system. The lagging power factor reduces the handling capacity of all the elements of the system. It is because the reactive component of current prevents the full utilisation of installed capacity.

The above discussion leads to the conclusion that low power factor is an objectionable feature in the supply system