This post contains an article published by a small cohort within PSC’s UK team including Dr. Mahmoud Elkazaz, Dr. Carlos Ferrandon-Cervantes, Raj Hirani, Jonathan Cervantes and Andrew Eviston. The group meets regularly to collaborate on topical issues of the day, shares the researching and writing effort across the team, and presents internally before publishing.
Every year, National Grid ESO publishes the Operability Strategy Report as part of the System Operability Framework, highlighting the opportunity areas to maintain a safe and reliable grid operation. The report identifies these requirements into five key areas: Frequency, Stability, Voltage, Thermal, and Restoration. This blog post elaborates on the ancillary services focused on frequency control and how stakeholders can participate in achieving a more sustainable grid.
Frequency and voltage: an intrinsic link
Frequency and voltage are two variables traditionally analyzed under different paths, although they are fundamentally related. Lately, with the rapid increase of Renewable Energy Sources (RESs) in the energy landscape, the coupling between them has become more significant. Here’s a quick description of such a relationship. After a fault happens in a system causing a transmission line and a generator to trip, both voltage and frequency will decline, followed by a loading increase of the lines thus the power out of that generating area will decrease and consequently affect the frequency in the system. As the power out of the area declines, the voltage starts to recover to pre-fault levels. As the voltage increases so does the power out of the area, and frequency then increases. This oscillation of power, voltage and frequency can last for several seconds. During this period, frequency response starts acting with the attempt to recover the frequency. The impact of this combined effect may be reduced with dynamic voltage support strategies. This will help to recover and maintain the voltage, which will support the recovery of frequency.
Frequency support ancillary services
The UK’s National Grid needs energy users (i.e. prosumers) to provide frequency response services. Participating providers (think generators, storage providers and aggregated demand-side response) are expected to act quickly to reduce demand, switch to backup generation, or increase generation when instructed by National Grid to help stabilize the grid. This service is called Firm Frequency Response (FFR). The service can be dynamic – energy changes in line with system frequency – or static – energy change occurs at present frequency and remains at a set level relationship. FFR is one of the National Grid’s most valuable balancing services on a £/MW hour basis. It’s billed as giving participants and the ESO a degree of stability against price uncertainty under the mandatory service arrangements. National Grid buys FFR services through a monthly electronic tendering process. Service providers can participate in the tendering process once they have passed the pre-qualification assessment and can tender either for a single month or for several months.
PSC has experienced first-hand how the frequency dynamics are evolving in the power system, including the voltage relationship. Interesting results have been found, pointing out that certain power systems still have the robustness to handle severe generation and load imbalances.
Whether your project is in an early stage of identifying FFR opportunities or advanced in system design, PSC has the experience to support achieving your goals. Please find out more about our capabilities in this area and contact us to talk about the first steps.
 Frequency Based Emergency Disconnection Policy Review for the Nordic Region – ENTSOE, [online]: https://www.statnett.no/globalassets/for-aktorer-i-kraftsystemet/utvikling-av-kraftsystemet/nordisk-frekvensstabilitet/frequency-based-emergency-disconnection-policy-review-for-the-nordic-region-v1.0.pdf