power factor,power factor correction
power factor
POWER FACTOR is the ratio between the useful (true)
power (kW) to the total (apparent) power (kVA)
consumed by an item of a.c. electrical equipment or a
complete electrical installation. It is a measure of how
efficiently electrical power is converted into useful
work output. The ideal power factor is unity, or one.
Anything less than one means that extra power is
required to achieve the actual task at hand.
All current flow causes losses both in the supply
and distribution system. A load with a power factor of
1.0 results in the most efficient loading of the supply.
A load with a power factor of, say, 0.8, results in much
higher losses in the supply system and a higher bill
for the consumer. A comparatively small improvement
in power factor can bring about a significant
reduction in losses since losses are proportional to the
square of the current.
Power factor correction is the term given to a
technology that has been used since the turn of the
20th century to restore the power factor to as close to
unity as is economically viable. This is normally
achieved by the addition of capacitors to the electrical
network which compensate for the reactive power
demand of the inductive load and thus reduce the
burden on the supply. There should be no effect on the
operation of the equipment.
To reduce losses in the distribution system, and to
reduce the electricity bill, power factor correction,
usually in the form of capacitors, is added to neutralize
as much of the magnetizing current as possible.
Capacitors contained in most power factor correction
equipment draw current that leads the voltage, thus
producing a leading power factor. If capacitors are
connected to a circuit that operates at a nominally
lagging power factor, the extent that the circuit lags is
reduced proportionately. Typically the corrected power
factor will be 0.92 to 0.95. Some power distributors offer
incentives for operating with a power factor of better
than 0.9, for example, and some penalize consumers
with a poor power factor. There are many ways that
this is metered but the net result is that in order to
reduce wasted energy in the distribution system, the
consumer is encouraged to apply power factor
correction. Most Network Operating companies now
penalize for power factors below 0.95 or 0.9.
Why improve power factor ?
The benefits that can be achieved by applying the
correct power factor correction are:
Environmental benefit. Reduction of power
consumption due to improved energy efficiency.
Reduced power consumption means less greenhouse
gas emissions and fossil fuel depletion by power stations.
Reduction of electricity bills
Extra kVA available from the existing supply
Reduction of I2
R losses in transformers and distribution
equipment
Reduction of voltage drop in long cables.
Extended equipment life – Reduced electrical burden on cables
and electrical components.
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