With millions more electric vehicles and heat pumps expected to be connected to the electricity distribution network over the next decade, an extended power outage under severe weather conditions would lead to a sudden demand surge at levels far higher than normal peak levels as electrical devices are reactivated.

Known as a “Cold Start” scenario, Energy Systems Catapult collaborated with UK Power Networks (UKPN) under Network Innovation Allowance funding to investigate the behaviour of domestic electricity consumers and the distribution network supplying them under just such a simulated scenario in 2030.

The Innovation

Our Systems Engineering team utilised our Dynamic Energy Systems Simulation capability has an innovative simulation tool called EnergyPath® Operations (EPO). This includes not only physical models of the behaviour of energy-appliances and network assets (including full-featured network analysis via load-flow), but also the ability to link this to simulations of business processes, markets, and digital infrastructure, to analyse the coupling between domains in the energy system and provide results and insights from a whole-systems perspective.

For this project, using EPO we simulated a portion of UK Power Networks’ real electricity distribution network. The simulation included a range of electrification scenarios for 2030, different outage parameters such as duration and restoration time, plus weather, consumer data and the network model. The dynamic simulation produced a range of metrics including power flows, voltages, asset loading and levels of unbalance.

The Challenge

When power is restored after a prolonged outage, electric heating systems and Electric Vehicle (EV) chargers will activate in large numbers on top of other household appliances. This temporary peak in demand could impact conductors and transformers in the electricity network.

Our simulations represented a real-world 11kV feeder, the “Dales Court Teed” feeder from Highfield Primary in Ipswich, which supplies 29 distribution substations. We combined dynamic modelling of the demands of 1,704 electricity customers fed by the feeder with load-flow analysis of both the 11kV feeder and synthesised Low Voltage (LV) networks linking it to the customers.

A range of electrification scenarios for 2030 were analysed, drawn from UK Power Networks’ Distribution Future Energy Scenarios, including up to 30% EV uptake and up to 20% uptake of electrified heating.

“Beast from the East” type weather conditions were used with -4°C temperatures, and outage durations ranging from a minimum of 8 to a maximum of 24 hours occurring on different days of the week and at different times.

The Outcomes

The key findings of the project included:

• Peak demand after outages could be more than double normal levels in 2030 (or 3x levels in 2020), both across the network and in terms of per-customer demand.
• Following a 24hr power outage, the increase in demand can last for up to three hours and can take up to ten hours to return to baseline levels.
• Individual customer demand in 2030 is 25% higher than today but increased after the power outage by almost 100% to over 4kW per consumer.
• Outage duration was seen to have the most significant impact on peak post-outage demand. LCT uptake scenario choice and restoration time/day had an observable but less significant impact.
• A small number of LV feeders could experience up to 50% overloading, though few events lasted longer than 20 minutes.
• Cold Start mitigations that should be considered include operational policies, network controls, demand-side flexibility and conventional. reinforcement.

The Recommendations

Findings suggest network operators should take steps to ensure their networks are robust to more significant Cold Start events by 2030 or sooner:

• Identify network regions with high risk of adverse effects from Cold Start, for prioritised investment. These could include areas with high likelihood of prolonged outages and/or areas with high volumes of expected LCT uptake.
• Analyse costs and benefits of management measures for high-risk areas to identify mitigation methods.
• Explore new methods to resolve challenges.
• Further develop policies, procedures, and standards from detailed modelling results, in particular updating design standards for new networks to accommodate Cold Start events.

Key recommendation: Consider the possible effects of Cold Start in high-electrification scenarios when planning network investment to 2050.