Are your voltage control systems ready for extreme weather?

It’s that time of year when motoring organisations issue their ‘get ready for winter’ checklists – batteries, lights, brakes, tyres etc. Wise words indeed. So in this article, John Humble makes the case that every asset on the grid needs to be in top condition for the worst of weather ahead – including voltage control systems.

Climate change means extreme weather events are predicted to increase in severity and frequency. The likes of Storm Arwen, which cut power to a million homes in Scotland and North East England in November 2021, can no longer be regarded as ‘freak’. Network operators must be prepared for devastating floods, gales, snow and cold. And the best way to do that is to ensure existing systems are in good working order – including the tapchangers and voltage control relays that are at the heart of managing supply and demand.

Both utility and large private operators have made enormous strides in recent years to ensure the resilience and reliability of their networks, with health indices and criticality ratings for the risks of failure, covering virtually every asset. Non-invasive monitoring of asset condition and fault detection, plus adherence to maintenance schedules, are standard practice. But events such as catastrophic storms have a way of exploiting the weakest links in defences.


A recent visit to a substation by our service engineers discovered a 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. This is a surprisingly common occurrence and ignores the risk that, in a worst case, a sticking tapchanger can cause a catastrophic transformer explosion, costing tens of thousands of pounds and months of downtime.

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. If elements of the grid that are considered critical are damaged, the burden often shifts to assets whose operability may previously have been considered of lesser priority. Should these in turn fail and cause outages, ‘low priority’ is not much of a defence against regulatory censure or, in the case of private operators, unhappy insurance companies and shareholders.


It is common good 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 – think Florida’s recent big freeze, Canada’s heat dome and September’s Libya floods. The UK is unlikely to remain exempt from such events for long.

The options for preparing 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.


We have certainly seen major growth in demand for service for the older tapchangers we support, in part because the current regulatory framework wisely allows spending on such things. These include Ferranti kit and the great majority of legacy brands which are still in service across the grid. Indeed, we often come across engineers who are amazed that everything from service parts and manuals, to expert advice and upgrades, is still available for tapchangers from manufacturers whose names have long faded into industrial history.

Many legacy tapchangers and transformers have been operating efficiently for decades: and will continue to do so for decades more, with regular maintenance – visual inspections, oil sampling, changing and keeping oil at the correct levels, plus replacement of worn mechanical parts. As operators increasingly realise, we take these essential voltage control assets for granted at our peril.


The importance of voltage control in preparing for more extreme weather events needs to be viewed in the wider context of radical changes facing the grid. New patterns of generation and consumption require it to be far more flexible, dynamic and responsive than ever before. Contrary to popular media concerns over the quantity of electricity needed to avoid winter outages, the principal issue is arguably that of balancing the grid to maintain available supplies to all consumers reliably.

Increasingly sophisticated automatic voltage control relays (AVCs) are becoming ever more essential to balance supply and demand profiles that can change in minutes or even seconds. A cloud passing over a large solar array can cause power to drop in an instant. Sudden wind blasts can cause turbines to cut out to prevent damage. Thousands (or millions in the future) of electric vehicle owners plugging in cars around teatime, together with heat pumps, cookers and other devices, will increasingly cause massive load spikes unless balancing techniques are applied more widely. The list goes 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 making the grid more capable of coping with the challenges ahead is simple enough, if hardly headline-grabbing: make sure every existing asset continues working as well as it can.