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Chart of the Week

2020

Cha-Cha Slide: COVID-19 & falling levels of inertia

Joe Camish Analyst

The level of inertia on the system is a key contributor to electricity system stability. In this Chart of the Week, we take a look at how changes in demand brought about by COVID-19 are impacting this. Inertia is an attribute of the system related to the energy stored in the rotating motors of synchronous generators (e.g. coal, gas, nuclear). It prevents system frequency from falling too quickly after a frequency disturbance (e.g. a generator trip) as inertia stored in these rotating motors provides resistance to system changes. It is effectively free frequency response the ESO can count on in the case of a sudden fall in frequency and is measured in Gigavolt Ampere Seconds (GVA.s). Typically, levels of inertia on the system will fall as the levels of synchronous generation on the system decline and asynchronous generation (wind, solar and interconnectors) increases. Demand falls of ~20% with COVID-19 has brought about a rapid recent increase in renewables penetration levels as a proportion of overall supply. Higher marginal cost synchronous generators have been the first to stop running with lower demand and as a result we are observing lower levels of inertia sooner than expected. During the Electricity National Control Centre’s (ENCC) weekly COVID-19 webinars, it was indicated the internal inertia limit for operating the current GB system is around 110GVA.s. The changes in demand levels have led to this being around 140GVA.s, a level the ESO was not expecting to be operating at ...

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