Keeping the grid stable – what is Loss of Mains Protection?

Graham Stein, Network Operability Manager at National Grid ESO, explains how Loss of Mains protection can keep the grid stable.

There is a lot more to keeping the lights on than you might expect. Safety is a priority for us, and one of the many protection systems which keep us all safe is called Loss of Mains Protection.

This is designed to check if a generator is still connected to the main network. If a power line disconnects for a few seconds, the generator at the end of the line is temporarily disconnected from the wider network. This can be unsafe and lead to damage to the generator or anything the generator is powering such as appliances in your home. Loss of Mains protection there to make sure generators shut down safely in these circumstances.

All generators that are connected to the distribution networks in Great Britain have Loss of Main Protection. This applies to all generating plant, irrespective of the type of electrical machine and electrical equipment used to convert any primary energy source, such as Wind or Gas, into electrical energy.

The larger the power generator the more checks we have in place. For example, a new 1200MW nuclear power station can’t just set up and connect to the network! One of the reasons for this is that disconnecting such a large generator is a big deal and has a major impact.

Although a small farm with one wind turbine is a tiny part of the network, thousands of these operating at the same time does generate a lot of electricity. If they all stop generating at the same time, they can have the same impact as a single large generator. This can happen when Loss of Mains Protection is too sensitive and can’t tell the difference between a local disconnection and the normal performance of the wider system.

We’ve helped to change distribution code requirements to make Loss of Mains protection less sensitive, and this has to be completed by generators by summer 2022. The setting has been changed from 0.125 hertz per second to 1 hertz per second. So if the line disconnects the generator will still shut down safely, but not if there is only a small change in voltage or frequency. The result is a network management benefit and which gives much more flexibility before a generators disconnect.

It will mean we’ll be able to operate the grid more efficiently and safely than ever before.

Some generators may find it difficult to make these changes on their own so along with the distribution companies we’re here to help.

Our Loss of Mains Protection programme is open and taking applications. We’ll provide funding and expertise to support anyone making the changes. We’re pleased how the programme is going so far. Over 500 generators have already signed up, and we’ve made payments to around 200 of these. More funding is available and we’re keen to hear from generators, or organisations which either has members who own electricity generation assets or works closely with them.

For more information or to see the full criteria for eligible generators visit the ENA website.