Power Factor
What is it?
Power factor is when electricity is being used inefficiently, mainly because of the use of motors. This wastes
power and money and increases greenhouse gas emissions. A detailed explanation is given below.
How does it work?
Appliances such as toasters and kettles use power efficiently but most motors in refrigerators, air
conditioners, pressure pumps, large motors in industry, etc, are inefficient users of power.
How does it become poor?
The power triangle (shown below) is useful in explaining power factor and how poor power factor comes
about. Motors and all appliances/equipment use electricity along the bottom of the triangle (shown in green)
– this achieves the work that needs to be done e.g. cooling the inside of a refrigerator. But motors, when
working inefficiently, draw energy heading upwards from the base of the triangle (shown in red). This
inefficient use of energy adds to the real power and increases the apparent power (shown in yellow). This will
cost commercial and industrial electricity users on their power bill and adds to unnecessary greenhouse gases
because more power is used to achieve the same effective work.
Most homes only get charged for real power, so there is no financial incentive for home owners to improve
their poor power factor. But most businesses get charged for what is called a “peak demand” for the apparent
power. This is the highest apparent power that is recorded by the meter for the monthly billing period.
Poor power factor can be corrected by adding capacitors to the circuit by what is called power factor
correction equipment (see over). Capacitors can remove the wasted energy and cause the apparent power to
equal the real power (power factor is then unity or 1.0 which is ideal). This will minimise the “peak demand”
apparent power charged by the power company. The only other way to reduce the peak demand charge is to
reduce you usage by not turning things on or using equipment with better star ratings.
Total energy usage
longer than it needs to
be (apparent power)
Motors cause wasted
energy here
Capacitors can be
connected and subtract
and correct poor power
factor
Power factor = Cos of angle
All appliances use power here (real power)
In summary - poor power factor is mainly caused by the use of electric motors and can be easily corrected by
the use of capacitors.
These capacitors are installed in a cabinet with a controller (see photo over) that governs how many of
capacitors are connected to the electricity supply at any one time.
Cooling fans
On/Off
Switch
Electronic
Controller
Low Voltage
Power Factor
Correction Unit
Capacitors
Inductors that help
protect the capacitors
Contactors that turn
capacitors on or off
Cost Justification for Installing Power Factor Correction Equipment
The installation of power factor correction equipment is justified:
When a “peak demand” charge is imposed by the electricity network supply company;
To reduce greenhouse gas emissions (becoming increasingly important).
Home owners are generally charged for real power (kilowatt hours [kWh’s]) and would not see any reduction
in their electricity charge if they improved their power factor, unless they have larger generators or pump
equipment.
Maintenance of Power Factor Correction Equipment
Once installed, your power factor correction equipment will only need to be monitored and maintained with
an annual check up.
1 Barnard St
Gladstone NSW 2440 Australia
Ph 02 6567 5181
Fax 02 6567 5182
Email: chris@powerlogic.com.au
www.powerlogic.com.au