Reactive power
Reactive power is electricity that supports magnetic fields in motors and similar equipment without doing useful work, and excessive amounts can be charged.
What it is
Reactive power, measured in kVAr, is the part of the current drawn by motors, transformers, lifts and air conditioning that sets up magnetic fields rather than doing the real work. Real work is measured in kW; the combination of the two is kVA. The ratio of kW to kVA is the power factor, where 1 means no waste.
Where you will see it
As an "excess reactive power" line on bills for sites with a half-hourly meter, measured in kVArh. The charge is set per kVArh by the local network operator as part of DUoS charges for half-hourly sites; the operator bills your supplier, which passes it on.
Why it matters
The charge applies only to reactive units above a threshold set in the network operator's charging statement, and the rate varies by region and voltage, so check your own bill or ask your supplier for the figures. A site with lots of motors and poor power factor can pay a lot for what is, in effect, wasted capacity. Power factor correction equipment can reduce this.
Example
A machine drawing 80 kW and 100 kVA has a power factor of 80 ÷ 100 = 0.8, below 0.95. If the site was billed for 150,000 kVArh of excess reactive power in a year at an assumed rate of 0.25p, the charge would be 150,000 × £0.0025 = £375. Fixing the problem with correction equipment might cost more than £375, so get a quote and a payback figure first.
Ask your supplier for a half-hourly data file and the reactive element of your bill, then ask an electrician whether correction is worthwhile.
Related terms
See supply capacity, three phase and half-hourly meters.
Common questions on this topic
Sources
General information only. Energy prices, rules and supplier terms change; check the latest position with your supplier, Ofgem or the Energy Ombudsman before you act.