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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