PFC Power Factor Correct system

How Do Power Factor Correction Capacitors Work?

A power factor correction capacitor (PFC capacitor) is a type of equipment that can help to improve the power factor of an electrical circuit.  

For example, if there’s a lagging current within the circuit, it will require additional power from the supply. This is also the case if there’s a leading current within the circuit, where the voltage waveform is slightly behind the current waveform. 

It is possible to balance the inductive load with the capacitive load which can then cancel out the extra power requirement from the supply.

A PFC capacitor will provide a leading current to help bring the measure closer to unity (power factor of 1). This is the point at which the voltage waveform and the current waveform are balanced.

The closer the measure is to unity, then the less power that is drawn from the supply. This reduces demand, which means less electrical generation is required.

An electrical circuit is a circular path that allows electricity to flow. This network is closed, enabling a return path for the current. The process of improving the power factor of an electrical circuit is called power factor correction (PFC). 

One of the ways PFC is achieved is by adding a capacitor to a circuit alongside your switchgear. The capacitor stores energy in an electric field which can help to improve the efficiency of your electrical systems which in turn will reduce electricity costs.

What are the main components of PFC capacitors? 

The main components that makeup PFC capacitors include the following: 

  • MKP capacitors
  • Fuse-gear
  • Switchgear
  • Contactors
  • Reactive power controller

Where there are fast-changing loads (usually welding loads) the contactors may be replaced with thyristor switches and the controller changed to one that can react quicker. This reduces the total kVA (kiloVolt Amperes) that is required, thus reducing the high transient-like peak currents that the transformer recognises.

There can be unwanted frequencies in an electrical circuit. The voltages that are in multiples of the power frequency are called harmonics. When harmonic currents are high, in-line reactors will be fitted to prevent any resonance and amplification of these currents.

In systems that have a low power factor, or that have other issues to do with the power quality, an Active Harmonic Filter will be the best option. The filter can be programmed to attenuate harmonics in addition to providing power factor correction. This is an increasingly popular way to provide PFC as the unit can be reappropriated, or added, in order to perform other power quality tasks.

Where in the machine would PFC capacitors be? And what exactly does it do? 

PFC capacitors are either fitted locally to the equipment that has a low power factor, such as a DOL (direct online) motor, or, generally, to the main board of the system. This is often called bulk correction. 

Capacitors are installed to an electrical circuit that have a poor power factor. They are added to the electrical circuit to ensure that the kVAR (kiloVolt Amps Reactive), which is required by the load, is supplied locally rather than by the main supply. This reduces the current drawn throughout the grid. By counteracting the current, the PFC capacitors will cut wastage which in turn will reduce electricity bills.

How are PFC capacitors fitted?

The bulk correction is split into discrete stages. They are brought in and out of the circuit via contactors controlled by a reactive power relay. 

The power relay monitors the power factor of the system and switches the stages required to meet the target power factor.

A reactive power controller is required to monitor the load by maintaining the reactive power output. To prevent surges associated with capacitor switching, soft-switching contactors are utilised with in-rush attenuating devices. 

The relay has a number of features that prevent capacitors from switching whilst still being charged.

The capacitors are fitted in parallel with the motor or circuits.  The initial fitting time is short, the capacitors require little maintenance, and it is usually very economic.

Who fits PFC capacitors?

A capacitor, along with all other power quality equipment, should be fitted and maintained by specialists in PFC. There are a lot of peculiarities unique to capacitor switched circuits that general electric maintenance personnel may not be able to recognise or deal with. 

Once fitted, PFC capacitors will help to improve electrical systems efficiency which will show a reduction in electricity bills. These benefits make a PFC capacitor highly valuable for places that have industrial electrical systems that may otherwise have been wasting power. 

If you would like to know more about PFC capacitors, then contact us, and we’d be happy to assist. 

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Power lines

5 Reasons Power Factor Correction Is So Important

Power Factor Correction (PFC) lowers the current drawn by an electrical system. It does this by producing the reactive power (KVAr) locally, thereby reducing the current drawn from the mains. Ultimately, this means that less power is used so you save money and lower your carbon footprint. PFC units can also improve safety and help you manage maintenance costs too. 


If you don’t already have power factor correction units fitted to your switchgear system, you could be operating with large inefficiencies and there are other potential issues you could run into too. Here are 5 reasons why power factor correction is so important.

1. Low carbon footprint

Managing your carbon footprint should always be a priority, especially when using electrical systems that draw a lot of power. Not only does this have internal benefits but it also improves your public image as sustainability is a priority for consumers. By using power factor correction, you can reduce the overall demand of the system and increase efficiency, reducing the strain you put on the electrical grid.

This is because the reactive power is no longer drawn from the mains, it is instead drawn locally. An electrical system draws active power (KVA) and reactive power (KVAr). Lowering the reactive power will increase the active power, thereby creating a more efficient system and helping you to use less energy.

The British Electrotechnical and Allied Manufacturers’ Association (BEAMA) estimates that you could reduce your carbon footprint by as much as 105kg per year for each power factor correction unit fitted. In a large facility, this adds up to an impressive improvement in carbon emissions with relatively little investment. For companies that are committed to being more eco-friendly, power factor correction is one of the most cost-effective changes that can be made.

2. The useful kW load can be increased without overload

By installing power factor correction units and reducing the reactive power, you can reduce the overall current carried by each circuit. This means that the useful kW load of each circuit can be increased further without the risk of overload that you would normally have. In many cases, this allows you to increase the capacity of the system without making expensive upgrades. Often, when introducing new equipment and machinery that puts a higher demand on the electrical system, you must make upgrades to increase the capacity. Installing power factor correction units is a more cost-effective and less disruptive alternative that could save you a significant amount of money.

3. They prevent Power Factor penalties

Often, there are power factor penalties on your electric bill if your system is below a certain efficiency threshold. It is usually added as an additional charge per kW of power used, and it quickly adds up. Generally, a power factor of 0.92 or lower will incur additional charges on your electricity bill. So, if you have an inefficient system that is already using more power than it needs to and you are then getting additional power factor penalties on top, you are likely wasting a lot of money. Power factor correction will help you avoid penalties by improving the power factor so it is above the threshold. As a result, you will see a significant drop in your energy costs overnight.

4. Improves voltage stability

A poor power factor leads to an increased current flow, which in turn can cause the voltage drop in the conductor to increase. The voltage going to the machinery is then lower, which can be a significant issue. Low voltage can cause serious damage to electrical components and electric motors are particularly susceptible to problems. An electric motor will draw more current when the voltage is too low, causing it to overheat. Essentially, equipment runs faster and hotter for a shorter period of time, so it is far more likely to malfunction. Not only is this a safety hazard but it also means increased maintenance costs too.

 

Power factor correction will reduce the voltage drop at the conductor, thereby increasing the voltage at the equipment. As a result, equipment runs more efficiently, it’s safer, and you experience fewer maintenance problems.

5. The maximum availability required for the system can be reduced

The maximum availability required for an electrical system refers to the maximum amount of power it can draw. Even though it may be drawing less power at certain points, the maximum availability must be met to ensure that the system continues running without interruption if the power it is drawing increases. In an inefficient system with a poor power factor, the maximum availability required is much higher and this places more strain on the power supply.

 

By fitting power factor correction units, the top amount of power that the system uses is reduced, so the top threshold also comes down. When the availability requirements are reduced, there is a smaller chance of interruptions caused by electrical faults or utility outages, so companies can avoid expensive downtime.

Power factor correction has numerous benefits and any business or organisation that wants to improve efficiency and save money should make it a priority. By reducing the power drawn by the system and avoiding penalties, you can cut your electricity bills and make your carbon footprint smaller at the same time. Stabilising the voltage and reducing the chances of overloading the transformer will also help you cut maintenance costs and improve safety.

Looking for a PFC solution?

If you do not already have power factor correction units installed in your switchgear, you are missing an excellent opportunity to boost efficiency and save money. But don’t worry, we are here to provide a PFC solution that works for you.

 

At AF Switchgear, we have over 45 years of experience manufacturing custom switchgear components to suit your needs. Our expert team can assess your electrical systems and advise on the best PFC solution for you. So, get in touch today to learn more about our services and how they could help improve your business!

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