Power Factor:

The power factor of an AC electrical power system is defined as the ratio of the real power flowing to the load to the apparent power in the circuit. It is dimensionless quantity and in the closed interval of -1 to 1.

Power Factor=True Power/Apparent Power.

A power factor of less than one means that the voltage and current waveforms are not in phase, reducing the instantaneous product of the two waveforms (V × I). Real power is the capacity of the circuit for performing work in a particular time.

Apparent power is the product of the current and voltage of the circuit. 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, the apparent power will be greater than the real power. A negative power factor occurs when the device (which is normally the load) generates power, which then flows back towards the source, which is normally considered the generator.

In an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. The higher currents increase the energy lost in the distribution system, and require larger wires and other equipment. Because of the costs of larger equipment and wasted energy, electrical utilities will usually charge a higher cost to industrial or commercial customers where there is a low power factor.

Linear loads with low power factor (such asinduction motors) can be corrected with a passive network of capacitors or inductors. Non-linear loads, such as rectifiers, distort the current drawn from the system. In such cases, active or passive power factor correction may be used to counteract the distortion and raise the power factor. The devices for correction of the power factor may be at a centralsubstation, spread out over a distribution system, or built into power-consuming equipment.

AC power flow has two components:
  1. Real power or active power (P) (sometimes called average power), expressed in watts(W)
  2. Reactive power (Q), usually expressed in reactive volt-amperes (var)

It shall be the responsibility of the HT Consumer to maintain an average PF of not less than 0.90.

If the power factor goes below 0.90 Lag, a surcharge of amount as penalty per unit consumed will be levied for every reduction of P.F. by 0.01 below 0.90 Lag.

Capacitors of appropriate capacity shall be installed to maintain Power factor.

It shall be the responsibility of the LT Consumer to maintain an average PF of not less than 0.85.

In respect of Electronic Tri-Vector meters, the recorded average PF over the billing period shall be considered for billing purposes. If the same is not available, the ratio of KWh to KVAh consumed in the billing month shall be considered.

The power factor is defined as the ratio of real power to apparent power. As power is transferred along a transmission line, it does not consist purely of real power that can do work once transferred to the load, but rather consists of a combination of real and reactive power, called apparent power. The power factor describes the amount of real power transmitted along a transmission line relative to the total apparent power flowing in the line.

Power factor is defined as the cosine angle between voltage and current in an alternating current (AC) circuit. 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.

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.


1.HT Consumers:

It shall be the responsibility of the HT Consumer to determine the capacity of the power factor correction apparatus in consultation with the manufacturers/suppliers of the equipments.

  • The Consumer shall maintain an average power factor of not less than 0.90 lag.In case this is not maintained, surcharge shall be payable as specified under Tariff schedule from time to time.

  • The average power factor is the ratio of KWh to the KVAh consumed during the billing month/period.

  • Billing Power factor shall be the average PF recorded in ETV meter. In case the same is not available, the ratio of KWh to KVAh consumed during the billing period and in case of non-availability of the above also, the PF obtained during the rating shall be taken.

2.LT Consumers:

To maintain the PF at not less than 0.85, LT installations including I.P sets but other than X-Ray installations shall be provided with capacitors of rating as indicated below:

Installed capacity Rating of P.F. correction
Apparatus for Motors (both single phase and three phase):
Upto and inclusive of 1 KW 0.4 RKVA (35 MFd.)
Above 1 KW Upto and inclusive of3 KW 1 RKVA
Above 3 KW KWRating x0.4 RKVA rounded off to the nearest integer

3.Whenever a fluorescent or vapour discharge lamp is installed, capacitors of adequate capacity shall be installed so that the P.F. of the fitting is not less than 0.85. The size of capacitors to be used with different types of lamps are given below:

Wattage of lamp Type of lamp
Fluorescent Mercury Vapour Sodium Vapour
20 watts Not less than 2 MFd.--
40 watts -do---
80 watts- 1x8 MFd.-
125 watts- 1x10 MFd.-
250 watts- 2x8 MFd.-
400 watts- 2x10 MFd 1x33MFd, + 1x10MFd
1000 watts- 2x33 MFd-
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