Power factor is a measure of the ratio of the 'total power' kVA (also known as apparent power) that is demanded by your site and the 'real power' kW that is used on your site. Show
The total power demand on the network is usually greater than the real power. The ratio of the real power to the total power is your power factor, a number between 0 and 1. The higher the power factor the more efficient your site is at utilising the supplied power. A business with a low power factor may result in higher capital expenditures and operating costs for the electricity network, compared to a similar business with a high power factor. These higher costs usually have to be passed on to all customers in the form of higher tariff rates. A simple analogy to explain power factor is that of a cappuccino. Here the mug must have sufficient capacity to contain both the coffee and the froth, corresponding to the total power. The froth represents the reactive power and the liquid represents the real power. We only gain real value from the liquid. How to measure your power factorThere are a variety of ways to measure your power factor:
If you don't have the skills in-house, you may engage an external specialist to help you to assess your power factor and identify any causes and solutions to improving your power factor. There are a variety of reasons that a site may have poor power factor but the main causes are:
There are a number of benefits to increasing your power factor:
Ways to improve power factorA poor power factor can be addressed in a number of ways. The most common approach is to install power factor correction equipment (PFC). PFC equipment is essentially a capacitor bank – which stores and provides reactive power when required. PFC equipment can be applied to separate pieces of equipment or installed in bulk to the sites main switchboard. A poor power factor can also be corrected by fixing the problem at its source. For example, by ensuring that motors are not oversized, selecting pumping equipment with electronic variable speed drives (VSDs), retrofitting VSD's where possible, and choosing equipment that has good power factor to begin with. Steps to identify and implement power factor correctionIdentify if your site has opportunity to improve power factorThere are a variety of ways to measure power factor, including:
Identify cause and solutions of poor power factorLarge sites will usually have in-house or contracted engineering or energy management expertise available who have knowledge of your plant and equipment and are often best placed to identify cause of poor power factors. Alternatively, either independent energy management consultants or suppliers/installers of power factor equipment will be required to identify the cause(s). Sites with the loads outlined above tend to have poor power factor. Designing solutions to power factorThere are a variety of ways to improve your power factor but the most common solution is to install capacitor banks which provide the needed reactive power to either the load or the entire site. Implementing power factor improvement measures is a specialist skill and using qualified and experienced providers to design a tailored solution should ensure the best result for organisations wishing to improve their power factor. We have compiled a list of independent PFC suppliers below, that you can use to start your journey. We don't endorse any party on the list, nor are you compelled to use any party on the list. This is purely for your reference and in consideration with your business needs. Once any power factor equipment or other changes have been implemented, it is important to measure and verify the changes in power factor that have been achieved and compare those to any pre-installation expectations. Installers of power factor correction equipment should be mindful to ensure the installation does not impact on our network eg audio frequency load control. MaintenanceOnce your power factor correction measures are implemented, like any electricity equipment, some maintenance is required to ensure the equipment continues to provide the expected benefits. Your supplier should provide advice on the necessary maintenance that is required to be undertaken. Power factor case studiesWe have previously implemented programs where we worked with large customers to implement power factor correction – benefiting both the customer and our network. Below is a selection of examples of case studies from those initiatives: Did you know...We require a customer to ensure that the power factor of any electrical installation measured at the consumer's terminals is not less than 0.8 lagging for installations supplied at low voltage? This is provided for in the Electricity Regulation 2006 (Qld). For all other high voltage connections, the power factor ranges are set out in the National Electricity Rules. Permissible range of power factor
Power factor is a measure of how effectively you are using electricity. Various types of power are at work to provide us with electrical energy. Here is what each one is doing. Working Power – the “true” or “real” power used in all electrical appliances to perform the work of heating, lighting, motion, etc. We express this as kW or kilowatts. Common types of resistive loads are electric heating and lighting. An inductive load, like a motor, compressor or ballast, also requires Reactive Power to generate and sustain a magnetic field in order to operate. We call this non-working power kVAR’s, or kilovolt-amperes-reactive. Every home and business has both resistive and inductive loads. The ratio between these two types of loads becomes important as you add more inductive equipment. Working power and reactive power make up Apparent Power, which is called kVA, kilovolt-amperes. We determine apparent power using the formula, kVA2 = kV*A. Going one step further, Power Factor (PF) is the ratio of working power to apparent power, or the formula PF = kW / kVA. A high PF benefits both the customer and utility, while a low PF indicates poor utilization of electrical power.
A steel stamping operation runs at 100 kW (Working Power) and the Apparent Power meter records 125 kVA. To find the PF, divide 100 kW by 125 kVA to yield a PF of 80%. This means that only 80% of the incoming current does useful work and 20% is wasted through heating up the conductors. Because Laurens Electric must supply both the kW and kVA needs of all customers, the higher the PF is, the more efficient our distribution system becomes. Improving the PF can maximize current-carrying capacity, improve voltage to equipment, reduce power losses, and lower electric bills. The simplest way to improve power factor is to add PF correction capacitors to the electrical system. PF correction capacitors act as reactive current generators. They help offset the non-working power used by inductive loads, thereby improving the power factor. The interaction between PF capacitors and specialized equipment, such as variable speed drives, requires a well designed system. PF correction capacitors can switch on every day when the inductive equipment starts. Switching a capacitor on can produce a very brief “over-voltage” condition. If a customer has problems with variable speed drives turning themselves off due to “over-voltage” at roughly the same time every day, investigate the switching control sequence. If a customer complains about fuses blowing on some but not all, of their capacitors, check for harmonic currents.
Power factor is the relationship (phase) of current and voltage in AC electrical distribution systems. Under ideal conditions current and voltage are “in phase” and the power factor is “100%.” If inductive loads (motors) are present, power factor less than 100% (typically 80 to 90% can occur). Low power factor, electrically speaking, causes heavier current to flow in power distribution lines in order to deliver a given number of kilowatts top an electrical load. The Effects?The power distribution system in the building, or between buildings, can be overloaded by excess (useless) current. Generating and power distribution systems owned by Laurens Electric have their capacity measured in KVA (kilo amps). KVA = VOLTS X AMPS X 1.73 (three phase System) / 1,000 With unity power factor (100%), it would take 2,000 KVA of generating and distribution network capacity to deliver 2,000 KW. If the power factor dropped to 85%, however, 2, 353 KVA of capacity would be needed. Thus we see that lower power factor has an averse effect on generating and distribution capacity. Low power factor overloads generating, distribution, and networks with excess KVA. If you own a large building, you should consider correcting poor power factor for either or both of these reasons:
There are several methods of correcting lower power factor. Commonly used are:capacity. Capacitor BanksThe most practical and economical power factor correction device is the capacitor. It improves the power factor because the effects of capacitance are exactly opposite those of inductance. The var of KVAR rating of a capacitor shows how much reactive power the capacitor will supply. Since this kind of reactive power cancels out the reactive power caused by inductance, each kilovar of capacitance decreases the net reactive power demand by the same amount. A 15 KVAR capacitor, for example, will cancel out 15 KVA of inductive reactive power. Capacitors can be installed at any point in the electrical system and will improve the power factor between the point of application and the power source. However, the power factor between the load and the capacitor will remain unchanged. Capacitors are usually added at each piece of offending equipment, ahead of groups of motors (ahead of motor control centers or distribution panels) or at main services.
Plants equipped with very large, intermitted inductive loads, such as large motors, compressors etc., may require switched capacitors; that is, capacitors are connected to individual motors or groups of motors. Therefore, they are only in action when the motor load is turned on. Or, capacity may be switched on and off at the substation, depending on measured power factor. The switching feature is only required if the capacitors needed are so large that they cause an undesirable leading power factor during times when large motors are turned off. For more information, read the “Reducing Power Factor Cost” Fact sheet (pdf) published by the U.S. Department of Energy. Note: Adobe Acrobat Reader is required to view and print pdf files. |