A poor power factor (PF) can lead to you paying over the odds on your electricity bill. David Knapper of ABB suggests you check your electricity bills now

Industrial and commercial electricity bills are rising fast, especially as all UK electricity suppliers are now imposing an excess reactive penalty charge where the average power factor is lower than 0.95 lag. Yet there is a simple and effective solution to hand in the form of power factor correction (PFC) equipment.

Power factor (PF) is essentially a measurement of how effectively a consumer uses their electrical power. The higher the power factor (and in an ideal case it would be 1) the more efficiently it is being used. Your electrical power has two components – active (working) power that performs the useful work and reactive (non-working) magnetising power. The PF represents the ratio between active and reactive power on the network.

Equipment such as AC motors, arc welders, furnaces, fluorescent lighting and air conditioning can all cause a poor power factor. The more inductive loads there are on your network, the more likely you are to have a poor power factor.

Why improve power factor?

Low power factor means poor electrical efficiency. If you don’t correct your power factor, the utility must provide the non-working reactive power in addition to the working active power. This results in the use of larger generators, transformers, busbars, cables, and other distribution system devices that otherwise would not be necessary. Since the utility’s capital expenditures and operating costs are higher, they will naturally want to pass these higher expenses down the line to you in the form of power factor penalties.

A low power factor could also restrict your expansion by limiting the capability to add further loads without major reinforcement of the site power infrastructure. And it might have implications for security of supply due to peak currents which could potentially cause fuse failure and tripping.

An additional driver for improving power factor is the growing need to reduce system power losses and consequent harmful generation of CO2. In fact, specific mention of power factor is made in the Building Regulations 2000, Document L2A ‘Conservation of fuel and power in new buildings other than dwellings’, the latest version of which came into effect in October 2010. This sets out the factors determining TERs (Target CO2 Emission Rates) and BERs (Building CO2 Emission Rates). As part of the ‘Enhanced management and control features’ the use of power factor correction to enable the whole building to achieve a power factor of at least 0.95 lag, allows for an adjustment in the BER.

For example, if the CO2 emissions due to electrical consumption were 70 kgCO2/m2/year without power factor correction (PFC), then the provision of PFC to achieve a PF of 0.95 would enable the BER to be reduced by 70 x 0.025 = 1.75 kgCO2/m2/year.

Correcting power factor

In electrical terms, capacitance is considered as a ‘reactive power’ component but in fact its characteristic in an electric circuit is to neutralise or compensate for the inductive reactive power. Therefore, capacitors are used to effectively offset a proportion of the reactive power drawn from the supply – reducing the reactive power supplied by the electricity company and improving the system power factor/efficiency. Excess reactive penalty charges can be immediately reduced or even eliminated completely.

Also, by improving the overall site operating PF, it may be possible to reduce the Authorised Supply Capacity (ASC), to be agreed with the Regional Electricity Company (REC), giving a further potential financial saving.

Capacitors are electrically very efficient, so their use on a network makes no significant increase in the active power requirement from the utility. Capacitor-based PFC equipment, such as ABB’s Vector series of automatic power factor correction equipment, is available in a variety of formats, either for installation within panels or free-standing, depending on the application. The benefits of PFC are most clearly demonstrated by some practical applications (see table below).

Take action now

I advise everyone with a 3-phase supply and on monthly billing to check their electricity bills. If there is a penalty charge, you should arrange a full power quality survey for your network – a low power factor might only be one of the symptoms of a range of problems such as harmonics, flicker and unbalanced load that can reduce the reliability and efficiency of electrical equipment. You will then be in a fully informed position to select the optimum PFC solution. And with typical payback periods of 12 months to two years, purchasing PFC equipment will be one of the easiest investment decisions you’ll ever make.

Ceramics manufacturing company

Maximum demand: 665kW

Power factor: 0.78

Cost of PFC including installation: £8k

Potential annual savings in reactive power charges and authorised supply capacity (ASC): £5.2k

Payback: 1.6 years

Food manufacturing company

Maximum demand: 637kW

Power factor: 0.85

Cost of PFC including installation: £5.8k

Potential annual savings in reactive power charges and authorised supply capacity (ASC): £3.3k

Payback: 1.3 years