Preparing power grids for extreme weather this winter

With the worst of winter weather arguably still ahead of us, John Humble of grid voltage experts Fundamentals explores how intelligent risk management, targeted maintenance and better communication across our networks are critical for preparing our power grids to keep the lights on.

How the grid can minimise winter outages

Popular belief is that the biggest challenge to the availability of electricity during extreme weather is generating capacity. That’s not necessarily so. For consumers, the greatest danger of lost power is likely to be failures of parts of the transmission and distribution networks. So how can we minimise this risk?

Increases in the frequency and severity of bad weather mean that so-called freak events are the new normal. Network operators must be prepared for more devastating floods, gales, snow and cold, which can take out whole substations and hundreds of towers, poles and wires, in a matter of hours.

While generation capacity can be dialled up by bringing reserve plant online, no amount of reinforcement of the grid can completely avoid the loss of some T&D assets during extreme weather events. The challenge for network operators is not just to fix physical damage as quickly as possible. It is to ensure their infrastructures and systems are as prepared as possible to withstand damage, keep electricity supplies and loads in balance, and restore power to the maximum number of end users.

The first line of defence is, quite simply, to ensure that existing assets are well maintained, fault-free and working correctly.

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Critical vs non-critical loads

Network operators understandably tend to focus maintenance and replacement on assets which are deemed critical i.e. there is a high risk of them failing and/or the consequence of their failure is high, particularly in terms of loss of service. The problem with extreme weather events is that they may take out well-maintained critical assets, so their roles fall to assets which have been classed as-non critical, with unforeseen results.

For example, our engineers recently discovered a substation tapchanger in extremely poor condition, with contacts that were totally worn out. It had not been maintained properly because, although the risk of failure was high, its criticality in terms of the consequences of failure was considered low.

That might be acceptable when the grid is operating in ‘normal’ conditions. But when parts of the grid are taken offline by things like storm damage, non-critical assets can rapidly become critical. In the case of the worn out tapchanger, there was a very high probability that it would have failed catastrophically, if called upon to do the work of its well-maintained equivalent.

Reinforcement or maintenance?

As in many industries, it is common practice for network operators to manage assets on the basis of N-1, where there is redundancy in system capacity, to allow for planned and unplanned downtime. Fine, when conditions are relatively normal and scheduled maintenance periods are planned. Less so, if the grid is under stress from storm damage and/or exceptional demand in extreme hot or cold weather, which could increasingly occur anywhere at any time.

The options for preparing power grids for extreme weather include moving towards N-2, with greater investment in additional asset capacity, to cope with worst case grid damage and exceptional loads. More realistically, the primary strategy must be to make the most of the grid we have, by ensuring that existing assets and systems are in good enough working order to deal with increased stresses. That includes assets which may currently be considered of low criticality, for the reasons cited above.

Invasive vs non-invasive maintenance

The question of what constitutes good network maintenance is a matter of horses for courses. Traditionally, assets such as switchgear and transformers were taken out of service on set time schedules and physically inspected for problems. Apart from the disruption caused, research showed that the inspection process itself produced a high probability of inducing faults.

Invasive maintenance has largely been replaced by increasingly sophisticated techniques for non-invasive condition monitoring and fault detection. In most cases nowadays, invasive maintenance or replacement of assets are based on the evidence of non-invasive measurements. Assets are accorded a health index, reflecting their condition and probability of failure – and the indices are collated in asset register databases.

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Maintenance and replacements are prioritised on the basis of risk, in terms of the probability of failure plus the consequence of failure. But as with the case of the worn-out tapchanger, circumstances such as storm damage can rapidly change the risks posed to the network by specific assets.

One of the key factors in making the new asset management regimes effective is to equip virtually every asset with communications capabilities, so their performance and condition can be monitored centrally, in real time. This is clearly essential for providing a ‘helicopter view’ of what has been affected by storm damage and responding immediately.

Life in the old dogs yet

Keeping legacy assets in good condition is increasingly recognised as one of the keys to network resilience. These include the thousands of electro-mechanical tapchangers and transformers that are essential for controlling voltages on the T&D system. Many have been operating efficiently for decades: and will continue to do so for decades more, with regular maintenance and upgrades.

Maintaining old kit requires approaches which are more hands-on than with newer electronic and digital plant – including visual inspections, oil sampling, changing and keeping oil at the correct levels, plus replacement of worn mechanical parts. However, legacy assets are increasingly being integrated into modern smart networks, by retrofitting them with communications and monitoring capabilities.

Keep maintaining and carry on

Headlines will continue to call for more generating capacity and reinforcement of the grid in an era of increasingly unpredictable and extreme weather. But one of network operators’ most powerful and affordable strategies for responding to the challenges ahead is plain enough, if hardly headline-grabbing: make sure every existing asset continues working as well as it can.

About the author

After becoming a member of Engineering giant GEC’s (latterly known as ALSTOM Grid) senior management team of their High Voltage Switchgear division in his late 20’s, John Humble went on to undertake several management roles in a career of over 25 years where he oversaw the delivery of hundreds of projects both domestically and internationally.

Approached to join Fundamentals in 2016 to develop their Tapchanger business, John in his role as Projects Director now manages a subsidiary business Ferranti Tapchangers in addition to their HV Service activity.