The rise in customer voltage complaints is one of the hot topics in play within the industry forum we recently hosted, “Voltage Matters.” The forum brings together members from across the electricity industry to share their concerns and experiences on all things voltage-related.
More than 60 forum members were presented with figures from a UK Power Networks 2023 study (Figure 1), revealing a 54% increase in voltage complaints from customers. Other grid operators are experiencing similar problems, which are almost certainly set to get worse.
Distribution network operators (DNOs) are understandably tempted to view this as a low-voltage (LV) problem and focus on applying localised solutions. But many customer complaints on LV networks are symptoms of problems much further up the grid.
The primary cause of voltage problems is that a grid built in the 1950s is being tasked with doing things that it was never designed to handle, such as coping with thousands of new distributed energy resources (DERs), low-carbon technologies (LCTs), and dramatic changes in patterns of customer demand. Meanwhile, many of our legacy transmission and distribution assets are degrading, through age, poor maintenance, and failure to modernise.
Rebuilding the grid from scratch is not an option. And to avoid unnecessary reinforcement, we need a system-wide analysis of where the problems lie in our existing infrastructure—and to apply the most cost-effective solutions to make it fit for purpose in the low-carbon era.
The Grid’s Outdated Model
The 1950s grid was designed to keep voltages high to overcome load-related voltage drops further down the networks. Power flows were in one direction, based on a top-down model, from centralised power stations to consumers and were relatively predictable.
Legacy grid assets were not designed to cope with today’s dynamic grid with large and rapidly changing peaks and troughs in both supply and demand, from intermittent renewable generation, domestic PV, EVs, and heat pumps. The network designers and planners never envisaged the sun breaking through clouds and suddenly adding megawatts of energy to the system, or thousands of EVs plugging in simultaneously.
As many Voltage Matters forum members reported, their biggest challenges are from voltage surges, with symptoms including EV chargers and PV inverters tripping out. Even more concerning, perhaps, is that over-voltages shorten the life of grid assets and customer equipment, waste energy, and increase carbon emissions. In extreme cases, they can cause catastrophic failure of customer equipment. And operators risk being sanctioned when voltages are outside regulatory limits.
Runaway Voltages
Existing grid assets such as transformers and tap changers are obviously under increasing pressure, leading to rapidly growing demand for new units. But there is a global shortage of supply with very long lead times.
Increasing the number of transformers and tap changers is not the only option, however. Our engineers are often called in to deal with problems associated with legacy transformers that have experienced “runaways” whereby tap changers run to their end positions and cause extremely high or low voltages on the network. Runaways are a result of poor maintenance (Figure 2) over the years leading to mechanical breakdown and/or failure of control system components.
The good news is that these issues can be fixed. Legacy assets were well engineered and have plenty of life left in them, given the ready availability of OEM (original equipment manufacturer) parts, repairs, refurbishment, and modernisation upgrades. Major assets such as transformers can be modernised to include new control panels, sensors, and communications add-ons. Expensive asset replacement can be avoided and effectively converted from dumb to smart units, fully integrating with modern voltage control systems and future-proofed for the low-carbon grid.
Taking Back Control
Herein lies a common and serious issue, however. Even the most well-maintained transformers and tap changers cannot work effectively without fully functioning control schemes—the interfaces between the intelligent decision-making device at the “front end” (voltage control relay) and the main asset that affects the voltage regulation for the network (the transformer tap changer [Figure 3]).
Control schemes involve complex wiring and a high degree of know-how to design and install. The problem is, many of those in service are broken or ineffective, but can be upgraded or replaced—which brings us back to runaway voltages.
Modern smart automatic voltage control relays (AVC relays) provide the intelligence and algorithms needed to change tap positions and keep voltages at optimal levels, even when managing highly dynamic load variations resulting from DER activity. The best of them include runaway prevention functionality.
Equipping the high-voltage (HV) sector of the grid with smart AVCs, linked via well-designed control schemes to well-maintained tap changers, delivers multiple benefits. It ensures that HV assets are running at optimal voltages. This increases their service life, reduces energy wastage, and emissions. It also goes a long way to addressing voltage issues further down in the LV networks—but not all of them.
Smarter Networks
We believe a whole-system approach is needed to apply smart voltage control solutions across the grid. For example, the latest AVC relays are at the heart of Electricity North West’s CLASS (Customer Load Active System Services) voltage control initiative, approved by Ofgem as an example for others to follow. It uses control relays in primary substations (Figure 4), which are linked to an advanced network management system in the control centre, to adjust voltages across a wide network area and provide demand response service. The CLASS system helps the whole energy system balance energy supply and demand.
We also continue to work with Northern Powergrid on its groundbreaking Boston Spa Energy Efficiency Trial (BEET), which uses data from customers’ smart meters to optimise voltages on the network. Like Northern Powergrid, we believe the use of smart meter data has enormous potential for optimising system voltages across the grid and reducing the number of LV issues.
Addressing voltage control applies all the way down to street level. Solutions such as low-voltage static compensators (STATCOMs), which use shunt-connected power electronics to control local voltages by sinking and sourcing reactive power, have a key role to play. Community-scale battery energy storage systems (BESS), which can both store and release energy at will, can also be important for balancing local power supplies.
The bottom line is that DERs and LCTs are increasingly causing voltage control problems for a grid built in a very different era. Many of the solutions to solve them already exist. But to fix them, we need to understand the system-wide causes, starting at the HV level and working down to LV.
—Jon Hiscock, PhD is CEO of Fundamentals.
