04 Nov 2021
Neil Weaver

How Frequency Response works - Modo Academy

To start off, here’s a quick reminder of how frequency itself works. Alternating Current, or AC, is a type of electrical current, in which the direction of the flow of electrons switches back and forth at regular intervals. The standard current used in Europe and Great Britain is 50 cycles per second, which means a frequency of 50 Hz. When we talk about system frequency, we’re referring to the frequency of the power on the electricity system. This is broadly the same across the distribution and transmission networks, and reflects the real-time balance of system demand and total generation.

If demand exceeds generation, frequency drops, and if generation exceeds demand, frequency rises. One of the roles of the National Grid Electricity System Operator, or ESO, is to maintain frequency at 50 Hz. This is the frequency that our power infrastructure is designed to work at.

If frequency deviates too far from 50 Hz, it can cause damage to infrastructure, and in some cases can lead to blackouts.

That means an operational limit of 0.2 Hz above or below 50, and a statutory limit of 0.5 Hz above or below 50. To manage frequency within these limits, the ESO procures frequency response services, which pay generation and demand assets to correct instantaneous supply and demand imbalances.

When system frequency drops below a certain level, these assets increase generation or reduce demand. When frequency exceeds certain levels, these assets reduce generation or increase demand.

There are really two types of frequency response procured by the ESO - these are pre-fault, which refers to a sort of constant fine-tuning that takes place to prevent deviations in frequency, and post-fault, which refers to actions that take place after major deviations in order to return frequency to nearer to 50 Hz.

Over the years, the ESO has trialled and put into practice a number of frequency response services, some of which procure pre-fault response and some of which procure post-fault response. Some examples of these services are Firm Frequency Response, Enhanced Frequency Response, and Dynamic Containment.

Across all of these services, participants are paid to provide frequency response, in pounds per megawatt per hour, regardless of the actual energy throughput the ESO requires.

To learn more about how Frequency Response markets work, and to see the rest of our Modo Academy series, be sure to check out the Modo platform.