Spikes still polluting the UK grid

Britain’s power supply is getting increasingly ‘polluted’ by voltage spikes that, at their most extreme, can wreak havoc with electrical equipment plugged into the mains. Electrical engineers will be familiar with the problem: it’s caused by harmonics sent back into the supply by rectifiers on DC equipment.

Put simply, this means that the enormous growth in direct current household electrical equipment since the 1970s – TVs, PCs, VCRs, phone chargers, low-voltage lighting – has a detrimental effect that spreads from each individual three-pin wall socket back into the national power supply network, causing peak voltages to waver beyond what’s regarded as an acceptable level. The result can be blown fuses, malfunctions, and, in the worst case, burnt-out motors.

Privatisation problems

While the inexorable growth of household electronics has been the major driver in this, there has been another, more recent factor that has made the problem worse: liberalisation – and privatisation – of the power supply network itself. This has seen a handful of big power stations replaced by a larger number of more localised plants, with more cabling adding to the resistance of the network, and more power plants switching in and out and adding to changes in that resistance. This tends to make the effects of ‘pollution’ in the network even worse, with parts of the UK’s electricity supply much dirtier than others.

Domestic consumers, despite being the biggest culprits, are largely oblivious to the situation, and look set to remain so. All domestic appliances rated under 16 amps – which cause the greatest part of the problem – meet the relevant standards and carry the CE mark. So for householders, it’s a case of ‘fit and forget’.

But parts of industry, and the electrical suppliers, are much more aware of the issue. Since the problem was first identified back in the 1950s, there have been regulations aimed at trying to mitigate its worst effects, issued by the Electricity Association, the trade body of the electricity producers.

The last set of regulations (called G5/3) came out in 1978, but since then the problem has worsened severely. The most recent set of rules, G5/4, came into play in March this year, and shows an attempt to tighten up control of the situation significantly.

There are growing implications for industrial power users in areas where the supply is particularly polluted. In theory, a company seeking to install a 7.5kW variable speed drive may have to apply to its local distribution network operator (the supplier) for permission to connect the equipment to the supply. And some network suppliers may have to invest in equipment to ‘clean up’ their supply to keep voltage within specified norms.

New regulations

‘The new regulations are substantially tougher than G5/3,’ said drives and motors principal engineer Geoff Brown from ABB Automation. Companies like his may have increasingly to offer technical additions to drives so that their tendency to pollute the supply can be filtered out.

‘Drives manufacturers will take it in our stride,’ he said. ‘But the risk is that variable speed drives, which are usually seen as energy-efficient tools, start to be seen as problematic. I think drives engineers will have to spend more time analysing a company’s overall systems, and take account of the supply network in which they are operating.’