Changes to system inertia and the impact on frequency response requirements

Previously held under moratorium from 23 June 2020 until 23 June 2022The changing power landscape and associated reduction of inertia in the power system, introduces concerns about the assurance of frequency stability and the adequacy of dynamic frequency responses at low inertia. In islanded power systems, like those of Ireland and Great Britain (GB), understanding the issues posed and deploying effective solutions benefit from an investigation concerning the changing demand for frequency containment reserve and containment limits following a credible loss risk. This thesis reviews frequency management in GB in the context of the changing energy landscape towards a lower inertia power system, identifying steps already taken by National Grid the GB Electricity System Operator (ESO) to address the issue, towards managing system frequency in a future lower inertia GB power system, without increasing the risk of system instability. A model and tools are developed to facilitate the studies presented in this thesis, and it is shown that methods can be employed to understand and define the factors influencing frequency behaviour, which can facilitate improved management of frequency and loss risk containment. In addition, an exchange rate method is proposed to convert the amount of reserve held between different frequency containment services, allowing one service to be compared and equated to another. In particular, a relationship is presented for converting response reserves from Primary to Enhanced response as they are defined in GB. This work provides insight into the need and provision of future frequency response services in GB. It is shown that at low-demand and low-inertia existing dynamic frequency containment services alone are insufficient to manage a credible loss risk, highlighting the changing need for dynamic frequency containment reserve and the need for, and value of, faster dynamic frequency response services. In addition, it is estimated that in GB the demand for Primary response will exceed Secondary response for at least 41% of the year by 2025/26, compared to at least 21% in 2016/17, reinforcing the growing need for additional frequency containment to supplement existing services. In GB, at present, there exists no dynamic restoration only product, as the services are bundled and the plants that deliver dynamic frequency containment also deliver dynamic frequency restoration as an extension of dynamic frequency containment, based on the operation of thermal plants. These services are procured as a bundle with demand for dynamic frequency restoration driving tenders in the commercial frequency response market. In order to meet the increasing demand for containment reserve, new frequency containment services are required, and these should be unbundled from frequency restoration services. A concept for a suitable framework of frequency containment services is presented that shows that deploying supplementary reserves as unbundled service manages frequency stability as effectively as the bundled services, while the inclusion of a rate of change of frequency management service improves performance at extremely low-inertia. In addition, to facilitate improved market participation and the competitive provision of containment services, it is argued that a shift in gate closure for the procurement of frequency containment services from month-ahead to day-ahead or even closer to real-time is required.The changing power landscape and associated reduction of inertia in the power system, introduces concerns about the assurance of frequency stability and the adequacy of dynamic frequency responses at low inertia. In islanded power systems, like those of Ireland and Great Britain (GB), understanding the issues posed and deploying effective solutions benefit from an investigation concerning the changing demand for frequency containment reserve and containment limits following a credible loss risk. This thesis reviews frequency management in GB in the context of the changing energy landscape towards a lower inertia power system, identifying steps already taken by National Grid the GB Electricity System Operator (ESO) to address the issue, towards managing system frequency in a future lower inertia GB power system, without increasing the risk of system instability. A model and tools are developed to facilitate the studies presented in this thesis, and it is shown that methods can be employed to understand and define the factors influencing frequency behaviour, which can facilitate improved management of frequency and loss risk containment. In addition, an exchange rate method is proposed to convert the amount of reserve held between different frequency containment services, allowing one service to be compared and equated to another. In particular, a relationship is presented for converting response reserves from Primary to Enhanced response as they are defined in GB. This work provides insight into the need and provision of future frequency response services in GB. It is shown that at low-demand and low-inertia existing dynamic frequency containment services alone are insufficient to manage a credible loss risk, highlighting the changing need for dynamic frequency containment reserve and the need for, and value of, faster dynamic frequency response services. In addition, it is estimated that in GB the demand for Primary response will exceed Secondary response for at least 41% of the year by 2025/26, compared to at least 21% in 2016/17, reinforcing the growing need for additional frequency containment to supplement existing services. In GB, at present, there exists no dynamic restoration only product, as the services are bundled and the plants that deliver dynamic frequency containment also deliver dynamic frequency restoration as an extension of dynamic frequency containment, based on the operation of thermal plants. These services are procured as a bundle with demand for dynamic frequency restoration driving tenders in the commercial frequency response market. In order to meet the increasing demand for containment reserve, new frequency containment services are required, and these should be unbundled from frequency restoration services. A concept for a suitable framework of frequency containment services is presented that shows that deploying supplementary reserves as unbundled service manages frequency stability as effectively as the bundled services, while the inclusion of a rate of change of frequency management service improves performance at extremely low-inertia. In addition, to facilitate improved market participation and the competitive provision of containment services, it is argued that a shift in gate closure for the procurement of frequency containment services from month-ahead to day-ahead or even closer to real-time is required