Power Factor Correction
In fundamental electrical theory, the current waveform created by a typical electrical load will lag the voltage waveform. The differential between these two elements is often referred to as the power factor. This can also be demonstrated using the power triangle where the apparent or real power is greater than it should be to compensate for an inefficient load.
Installations with predominantly inductive loads will generally have a poorer power factor than those with a higher proportion of capacitive loads. The more the current lags the voltage the worse the resultant power factor will be and the less efficient the installation will be.
The importance of a good power factor is becoming recognised with increasing clarity. Not only because of the year on year increase in energy costs but also because it can reduce the production of greenhouse gases. Companies anxious to demonstrate their green credentials will need to review the power factor of their building.
Reactive charges for poor power factor
Most DNO (Distribution Network Operators) who manage and distribute the power to users within the UK charge a penalty for consumers who operate an inefficient electrical installation called a “Reactive Power Charge”. Where applicable, these charges will be separately quantified on the bill and can be quite considerable depending upon the magnitude of the problem and the specific rates imposed by the DNO.
Reactive Power charges can be mitigated or completely neutralised by installing the appropriate type of Power Factor Correction equipment. The siting and specification of the PFC equipment should only be determined following a site survey by a qualified Engineer.
At Vector Ltd, we offer expert advice and engineering solutions to suit each application, which may warrant the specification of entirely different equipment. This will often depend on the percentage of non-linear loads, for example;
Less than 15% non-linear load:
Standard automatic power factor capacitors are suitable. Because harmonic currents can be imported into your facility from the utility network, +460V dielectric capacitors are always specified. These capacitors can absorb some harmonic current without damage
15% to 50% non-linear load:
In this instance detuned automatic power factor capacitors are suitable. Detuned capacitors employ reactors in series with each capacitor stage to limit the amount of harmonic current that is absorbed and to prevent resonance between the supplying transformer and the newly installed capacitor bank. It is important however to remove any existing capacitors prior to installation of a detuned bank as their presence on the network can change the tuning characteristics of the detuned bank.
Over 50% non-linear load:
In this instance filtered automatic power factor capacitors can be used but only after complete analysis of the network to ensure correct application. Filtered capacitors employ filter reactors in series with each capacitor step to produce a tuned resonant circuit which will offer a low impedance path to absorb a particular problematic harmonic (such as the 5th harmonic produced by variable speed drives). A filtered automatic bank will provide the necessary power factor correction and reduce the voltage distortion on the network. It is important however, to remove any existing capacitors prior to installation of a filtered capacitor bank as their presence on the network can change the tuning characteristics of the filtered bank.
In summary, the installation of power factor correction equipment will reduce loading on transformers (KVA – total power demand), which not only represents a saving on your energy bill, but also frees up capacity that may be required to meet future demand on the installation.
