Two generators tripping caused the biggest frequency drop for years, with widespread power outages as National Grid’s systems disconnected demand in order to limit the impact.
RWE’s 740MW Little Barford gas-fired power station reported that it had tripped first, followed by some units at Ørsted’s Hornsea offshore wind farm.
Strong winds led to exceptional volumes of renewable power on the system, and fewer thermal plant generating as a result. That reduced inertia on the system, reducing the available resources to manage the outages as frequency quickly dropped to 48.9hz – well below tolerance boundaries.
National Grid ESO said it took action to cut demand in some areas to protect the rest of the system. That led to outages across the country. The system operator said all areas were restored by 18:30, though transport networks and commuters were feeling the effects for the rest of the evening.
National Grid has to maintain the power system close to 50hz to keep it stable. In the past, it has relied on inertia in the system in order to regulate frequency.
However, inertia has been provided by the large spinning turbines of big power stations. As coal plant shuts down and gas load factors reduce as more wind and solar comes on stream, there is less available inertia.
National Grid is therefore more reliant on ‘synthetic inertia’ provided by companies responding very quickly using batteries, or turning large plant on or off, or fast acting forms of generation such as pumped storage, to balance frequency.
It pays companies to deliver frequency response – which usually helps to prevent large-scale outages.
National Grid aims to be able to operate the system entirely on renewable sources when practicable by 2025 and will therefore require greater sources of flexibility to keep the system balanced.
The incident will also have given businesses and critical infrastructure providers – such as hospitals, banks, airports and data centres – a clearer picture of the state of their back-up power systems.
Interested in demand-side response? National Grid, energy suppliers, aggregators, distribution networks and consultants will outline the direction of travel at The Energyst’s DSR Event, 11 September, London. Details here.