In the simplest terms, power factor is the measure of how effectively your electrical equipment converts electric current (supplied by your power utility) into useful power output. In technical terms, it is the ratio of Active Power (also known as Working Power and measured in watts or kilowatts (W or kW)) to the Apparent Power (measured in volt amperes or kilovolt amperes (kVA)) of an electrical installation.

The Active Power consumed by an electrical device, is used to perform a useful power output such as heat, light, mechanical energy, etc.

Inductive devices (such as electric motors, transformers, welding units, lighting ballasts and static converters) also consume Reactive Power (measured in volt ampere reactive or kilovolt ampere reactive (VAr or kVAr)) in order to generate a magnetic field. This magnetic field does not perform any “useful” work, but is required in order for the device to work. The reactive current drawn by an electrical device lags 90 degrees behind the active current drawn by it.

The Apparent Power drawn by an electrical installation is the vectorial sum of the Active and the Reactive Power drawn by the installation.

Various analogies have been used to describe poor power factor including the following:

Horse Pulling Cart

A cart on a railway track is being towed by a horse that is off to the side of the railway track. The pull directly between the horse and cart is the apparent power (kVA). The effective work by the horse is the cart moving down the track, being the active or true power (kW). The pull at right angle to the track does no effective work and represents the reactive power (kVAr).

The horse would ideally pull the cart directly down the railway track so the apparent power equals the real power, thus minimising wasted energy.

Beer with Froth

A large beer is ordered to quench the thirst of a thirsty individual. The beer has some froth on top that does nothing to quench the individual’s thirst – this represents the kVAr (reactive power).

The beer does quench the thirst – this represents the kW (real power).

The total contents of the mug (the bear and the froth) represent the kVA or apparent power. The glass must be full of beer with no froth for the person to gain maximum benefit from the glass of beer. It is the same for maximum efficiency with power as the system should not be drawing any kVAr (or froth in the analogy).

Power factor correction is the process of improving a low power factor present on a power system by means of installing power factor correction capacitors and in so doing, increase the ratio of active power to apparent power.

When the apparent power is greater than active power, then the utility provider must supply the excess reactive power AND the working power.

Power capacitors act as reactive power generators and they reduce the total amount of current a system draws from the grid.

Reduction in apparent power (also known as maximum demand)
Lower electricity bills
Increased system capacity (free up capacity on your supply transformer)
Reduced voltage drop on the supply transformer and supply cables
Reduced transmission losses
Reduced carbon footprint

Industries where motors are operated at less than full load (cyclical processes): Saw Mills
Plastic: extrusion and recycling
Industries using machine tools, stamping machines, welders, compressors
Foundries
FMCG industries
Bottling plants
Refrigeration plants
Grocery store


The power utilities in most industrialised nations charge users a penalty when their power system’s power factor drops below a certain level, usually below 0.90. This power factor surcharge covers the electric utility’s cost of supplying your power system with additional reactive power.

In South Africa, no “fines” are imposed as yet, although Eskom intends to introduce fines in the near future.

Some South African municipalities (i.e. City Power) do charge for excessive reactive power consumed, which is a form of “fine”. City Power charges for all reactive power consumed below a power factor of 0.96!


Accurate measurements of the electrical load profile of a potential customer are required to determine the most cost effective power factor correction solution.

Uncorrected power factor
The worse the uncorrected power factor, the shorter the payback period
The higher the target power factor, the longer the payback period
Power factor correction between 0.96 and 0.98 usually provides the best return on investment (there are certain exceptions where a target power factor of 1 is advisable).

Current and voltage harmonics present in the system. If these are elevated, blocking reactors might have to be fitted in series with each of the capacitor banks. This has a significant implication on the total cost of the power factor correction panel
Load changes (frequency and amplitude): if the load changes of an installation are significant ( i.e. mesh welding), thyristor controlled switching of the capacitor banks is then required as standard contactors are too slow in response
Unbalanced loads
Other factors influencing the payback period are:

Target power factor: the “law of diminishing returns” applies: as the corrected power factor approaches 1.00, ever increasing amounts of reactive compensation are required for fairly small reductions in apparent power. A target power factor correction of between 0.96 and 0.98 usually provides the best return on investment (there are certain exceptions where a target power factor of 1 is advisable).
Equipment costs, determined by:
Quality of key components
Capacitors
Contactors
Controller
Blocking reactors

Enclosure:
IP rating
Material
Non-standard dimensions

Voltage (400/550V vs. 3.3/6.6/11/22kV)
Required protection of the power factor correction panel:
isolator (fused or not)
MCB
Ambient and operating temperature constraints
Installation constraints
Cable length
Protection (LV distribution)
Access constraints
After-hour installation

Applicable maximum demand tariff levied by the power utility. In South Africa, there are significant differences in tariff. Herewith some examples (2012 rates):
Eskom Nightsave Urban (small) summer: R11.25/kVA
Ekurhuleni Tariff C summer: R68.03/kVA
JHB City Power (LPU LV Tariff) summer: R168.67/kVA

Pay-back period for investments in well designed power factor correction systems are usually between 3 and 18 months. Power factor correction equipment of good quality, has a life expectancy of at least 10 years.

Electricity has until recently been a cheap commodity in South Africa (and Southern Africa in general). The payback period of an investment in power factor correction has therefore been fairly unattractive. The recent tariff hikes have significantly reduced the payback periods and will continue to do so in the short to medium term.

Power factor correction equipment dates back to the 19th century and is based on proven scientific concepts.

There is no financial benefit under these circumstances BUT, it could free up capacity on your supply, allowing you to add more equipment and in so doing increase production or avoid relocation to different premises with a larger power supply.


Power factor correction reduces the total current drawn from an electrical distribution network (which affects systems such as the power stations, distribution grid and supply transformers). In so doing, the heat or transmission losses incurred on these systems are reduced. Power factor correction therefore only has a minor impact on your carbon footprint.


It is not advisable to over-compensate an electrical installation as there is no benefit in doing so.


An electrical audit of your installation with specialised electrical instruments is required in order to determine your exact requirements.


A power audit can take anywhere between a few minutes and a few weeks. This time will vary depending on the size and scope of your power system, as well as your company’s location.


It is usually possible to replace a specific capacitor or any other component for that matter, without having to replace the whole panel. However, when the extent of the damage is significant, it can be that the replacement of the complete panel is a financially more attractive option.


There are no moving parts in a power factor correction panel, which can be serviced. The most important maintenance item is to ensure that the panel remains clean and that the ventilation system remains fully operational. It is crucial that the air intake filters are kept clean. Excessive operating temperatures will negatively affect the life expectancy of the capacitors.

The service intervals are mostly determined by your environmental and operating conditions.


The cost per kVAr for large installation is the lowest with MV power factor correction equipment. The cost of MV switch gear however means that large banks are selected, which makes for course power factor adjustment in small electrical systems.


Automatic power factor correction is usually installed in proximity of the main distribution board.

For electrical systems with only a few large loads, it is usually cheaper to install suitably rated capacitors directly onto the inductive loads.


The reactive power of a capacitor, as shown on its data plate, is always indicated at a specific voltage. If the voltage of an installation is lower than the rated capacitor voltage, then the output if the capacitor is negatively affected.

For example: a capacitor of 10 kVAr rated at 440V will only provide 8.3kVAr if the system voltage is only 400V!

This is an important factor which must be taken into consideration when determining the reactive compensation requirements of an electrical installation.


If you connect the correct value of capacitors in the supply to an induction motor, you will reduce the current flow from the supply to the point where the capacitors are connected. If you measure the current in the supply between the capacitors and the motor, you will find that the current does not change. The current into the motor is independent of the connection of the capacitors. The efficiency of the motor is unchanged.


In most instances, not. The motor losses are not changed so the temperature rise of the motor remains the same. However, if you install a suitably rated capacitor directly onto the motor, you will reduce the current flowing through the supply cable and in so doing, reduce the volt drop on the cable. This in turn can result in a reduction of the total current drawn by the motor, which will reduce the heat (Watt) losses (=I2R) of the supply cable.


Manufacturers of diesel-electric generator sets usually indicate the maximum output of their equipment at a specific power factor, usually 0.8.

This means that if you purchased a 1000kVA generator set, you actually bought an 800kW system. Installing power factor correction would in theory allow you to increase the output of the set to 1000kW. The alternator will be able to cope with this load, but the diesel engine will not.

Another potential problem is that under conditions of significant and sudden load reductions (for example a major fault in the system), the power factor correction system will not respond fast enough to reduce its reactive power output to match the reduced requirements. The excess reactive power generated by the power factor correction panel has no-where to go and the system voltage will increase dramatically. This usually results in significant damage to the generator, the power factor correction panel and the associated electrical distribution system. Genset suppliers usually clearly indicated in their warranty conditions that power factor correction which is in operation with the generator will render their warranty null and void.


No, the addition of power factor correction may reduce the current drawn by your residence, but this will not result in a reduction of your electricity costs. This is due to the fact that you are only being billed for your active power consumption (kWh) and not for maximum demand (kVA) nor for your reactive power consumption (kVArh).

Power factor correction in a residential application is primarily only used to prevent the main incomer circuit breaker from tripping by reducing the total current drawn. The power factor correction panel supplies most of the reactive current drawn by the inductive components in your residence, and in so doing, reduces the total current flowing through the incomer circuit breaker.

There is no financial benefit in doing so, there is only a “comfort” benefit.


No, the addition of power factor correction will reduce the current drawn from the supply in situations where there is an inductive current flowing and the correction is equal to or less than the inductive current. The reduction in current can reduce the losses in the supply, but no appreciable loss reduction will occur within the residence.


They are a distortion in an electrical network created by non-linear electrical devices such as VSD’s, DC drives, soft starters, UPS’s, etc
Harmonics are a component of a periodic wave which has a frequency which is a multiple of the fundamental frequency of 50 Hz: i.e. 150Hz is third order harmonic frequency
They are a steady-state phenomenon, not a transient condition
3-phase non-linear loads typically create 5th, 7th, 11th and 13th harmonic
2-phase non-linear loads typically create 3rd order harmonics and higher order multiples of 3
Total harmonic distortion of a waveform (THD) = the level of voltage or current harmonic distortion existing at any point on a power system


Power factor correction equipment does not generate harmonics but it can amplify existing harmonics present in a network, which will affect sensitive electronic equipment in its vicinity. It is therefore recommended that harmonic blocking reactors be fitted in series with capacitor banks when existing harmonic levels are elevated. The blocking reactors present the harmonics from reaching the capacitors and can therefore not be amplified by them.


Inexplicable electronic component failures
Overheating electrical cables
Protection equipment such as circuit breakers and fuses tripping for no apparent reason


A total harmonic distortion (voltage) or THD(V) of 2.5% and a total harmonic distortion (current) or THD(I) of 15% are usually considered safe levels.


Depending on the severity and source of the harmonic distortion, active or passive harmonic filters can be installed to reduce the harmonic levels present in a system.


Alpha Power Solutions has, in conjunction with Comar Benelux (Belgium) over 27 years of experience in the field of power factor correction and harmonic filtration.

Alpha Power Solutions was established in South Africa in 2007 in order to better serve the South African market as Comar Benelux was unable to provide the required service levels from Belgium.


All our equipment comes from Europe as a finished product. All systems are tested in Belgium before shipping to South Africa.

Alpha Power Solutions stock a large quantity of finished and semi-finished modular power factor correction systems as well as spare components, in South Africa.

Any non-standard systems can be brought into the country within 1 to 2 weeks (air freight) or 6 to 8 weeks (sea freight), from receipt of order.


Alpha Power Solutions operates in sub-Saharan Africa.



We prefer working through reputable electrical contractors and will assist them with preferential pricing and technical assistance where required.


Our equipment is warranted against defects in material and workmanship for a period of 2 years from date of purchase.


Eric Solot holds a Master of Applied Engineering (Electrotechnology) from the University College in Ghent (Belgium). He is the Managing Director and one of the Directors of Alpha Power Solutions, which specializes in power factor correction and harmonic filtration.