Under the auspices of the Distribution Code Review Panel, National Grid Electricity System Operator and the Distribution Network Operators (DNOs) have been working with stakeholders to determine how the loss of mains (LoM) protection fitted to all small generators connected to the distribution system needs to be updated. The drivers for these changes include the growth of interconnector capacity, the replacement of traditional large steam turbine driven synchronous alternators connected to the transmission system with smaller solar and wind generation predominantly connected to the distribution system. This in turns leads to a general decline in system inertia, volatility of system frequency and the inadvertent tripping of vector shift relays due to secured events on the transmission system – all of which are recognized in the recommendations for new LoM settings.
This work has been undertaken by the DC0079 Distribution Code Review Panel working group (and before that the GC0035 working group), which has implemented changes to date that have affected all generation in the size range 5MW to 50MW, and laid down requirements for all new generation connecting to the distribution system.
DC0079 has now completed its work and has recommended to Ofgem that the settings which are required for new generation are now also applied retrospectively to all existing generation (including those in the 5-50MW range that use vector shift relays as their method of LoM protection), with the exception of small type-tested generation below 50kW registered capacity. This will result in a modification to the Distribution Code requiring all qualifying generators to be compliant with the new settings by May 2022.