Tech Info

PF Correction

Reactive Power PF Correction Capacitors Harmonics PCB Disposal PCB Dangers


What is Power Factor Correction ?

Power factor is the relationship between working (active) power
and total power consumed (apparent power). Essentially, power
factor is a measurement of how effectively electrical power is
being used. The higher the power factor, the more effectively
electrical power is being used and vice versa.

A distribution system’s operating power is composed of two parts:

Active (working) power
Reactive (non-working) magnetising

The ACTIVE power performs the useful work. The REACTIVE power does not as its only function is to develop magnetic fields required by inductive devices.


pfangle.gif (25336 bytes)

Generally, power factor decreases ( increases) with increased
motor loads. Therefore, when more inductive reactive power is
needed, more apparent power is also needed. This geometric
relationship of apparent power to active power is traditionally
expressed by the right angled triangle relationship of:

Cos = p.f. = kW / kVA

Why Improve Low Power Factor?

Low power factor means poor electrical efficiency. The lower
the power factor the higher the apparent power drawn from the
distribution network.

When low power factor is not corrected, the utility must provide
the non-working reactive power IN ADDITION to the working
active power. This results in the use of larger generators,
transformers, bus bars, cables, and other distribution system
devices, that otherwise would not be necessary. As the utility’s
capital expenditures and operating costs are going to be higher,
they are going to pass these higher expenses down the line
to industrial users in the form of power factor penalties.

High power factor
eliminates utility power factor penalties
High power factor
reduces the IR losses of transformers and distribution equipment
High power factor
stabilises voltage levels

The following diagram illustrates the relationship of power factor to total current consumed. With a power factor of 1.0, given a constant consumed power load, the 100% figure represents the required useful current.

capsratings.gif (33087 bytes)


As the power factor drops from 1.0 to .9, power is used less
effectively. Therefore, 10% more current is required than when
the power factor was 1.0 to handle the same load.

A power factor of .7 requires approximately 43% more current;
and a power factor of .5 requires approximately 100% (twice
as much) as required when the power factor was 1.0 to handle
the same load.

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Copyright 2000 Philip J. Alcorn & Co.

While every care is taken to ensure that the information contained in this publication is correct, no legal responsibility can be accepted for any inaccuracy. The Company reserves the right to alter or modify the information contained herein at any time in the light of technical or other developments.