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. The factors have a significant impact on the ROI of an investment in PFC equipment:
Uncorrected and target power factor
- The worse the uncorrected power factor, the shorter the payback period
- 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 associated 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).
- 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 (for example a mesh welding factory), thyristor controlled switching of the capacitor banks is then required as the response time of standard contactors is too long for this type of application
- Unbalanced loads
Other factors influencing the payback period are:
- Equipment costs, determined by:
- Quality of key components
- Blocking reactors
- Quality of key components
- IP rating
- 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)
- Ambient and operating temperature constraints
- Installation constraints
- Cable length
- Protection (LV distribution)
- Access constraints
- After-hour installation
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 doing so, 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 doing so, 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 allows 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 of 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 indicate 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
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 30 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.
We can service and repair any make of power factor correction equipment.
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.
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