Reactive Power

What is Reactive Power?

Some equipment used in industrial and commercial applications requires an amount of ‘reactive power’ in addition to the ‘true power’ requirements. This reactive power generates the magnetic fields which are essential for inductive electrical equipment (such as transformers, motors and welders) to operate.

Reactive power is measured in units of kVAr (kiloVolt Amperes reactive), whilst ‘true power’ is measured in kW (kiloWatts). In general terms the lower the power factor, the greater the amount of reactive power required. The highest power factor is unity, 1.0 however some equipment can operate at power factors as low as 0.4. The power factor can be calculated from the power triangle shown below:

Reactive Power Charges

A number of Distribution Network Operators levy a reactive power charge if the number of reactive units consumed exceeds a pre-determined percentage of kilowatt hours consumed, which means that the amount of charges will vary from site to site, and even from month to month. These charges are passed on to our customers at cost as levied by the distribution company and are not included in the rates agreed on your quote.

As an example, in the former Eastern Electricity area (EDF) such charges only apply to the number of reactive units in excess of 33% of the total number of kilowatt hours consumed e.g. Assume 10,000 kWhs consumed and 5,000 reactive units recorded over a billing period, then charges would be based on 1,700 reactive units;

i.e. 5,000 – (0.33 x 10,000).

Energy suppliers will invoice these charges separately from your main bill, in accordance with the terms of your contract with them. Payment for these invoices is due promptly according to the payment terms and method agreed on your contract.

Can you reduce  Reactive Power Charges?

Customers wishing to reduce or even eliminate reactive power charges can consider doing so by improving the site’s power factor, to a level close to unity, i.e. 0.95-0.97.

This is possible by installing power factor correction equipment. Power Factor Correction equipment consists of capacitors with associated control and switchgear. Capacitors draw reactive power, but in an ‘opposing direction’ to that drawn by typical business plant and equipment. The net effect is a reduction in the amount of reactive power, and therefore a lower level of kVA which may in turn lead to a lower available capacity charge each month.

In addition to reducing Reactive Power charges there may be other benefits in Power Factor Correction;

• Potential Reduction in any kVA leading to possible reduction in demand related charges.
• May provide additional capacity from existing connections without the need for system reinforcement.
• Likelihood of reducing overheating electricity distribution equipment.

Of course there are costs associated with the installation of PFC equipment. Systems can be installed from £500 but this may be negligible when compared against the reactive power charges that would otherwise have been incurred.

If required Billscutter, via a specialist power factor company, can arrange for an analysis of a sites existing power factor and quotation in order to determine the cost benefit of installing Power Factor Correction equipment.

Should you require any further information on Reactive Power, or Power Factor Correction Equipment please contact us.