The Role of Interconnectors in GB Grid Stability

What Are Interconnectors?

Interconnectors are high-voltage cables — typically subsea — that link the GB electricity grid to neighbouring countries. They allow power to flow between markets, balancing supply and demand across borders. As of 2026, GB has ten interconnectors:

Total interconnector capacity: ~10,300 MW — roughly 30% of typical GB demand (~28–35 GW), and over 20% even of the winter peak.

Interconnectors and Inertia

Here's the critical point that many people miss: interconnectors provide zero synchronous inertia to the GB grid.

All of GB's interconnectors use High Voltage Direct Current (HVDC) technology. The AC-DC-AC conversion fully decouples the GB grid from the connected system. When France's nuclear fleet provides inertia to the French grid, none of that rotational energy is "felt" by the GB system through the IFA interconnector.

This means that even when an interconnector is importing 2,000 MW into GB, it contributes the same inertia as a 2,000 MW wind farm connected via inverters — essentially zero synchronous inertia.

The Largest Credible Loss Problem

Interconnectors create a specific risk: they can be the largest single infeed to the GB system. If the NSL interconnector is importing 1,400 MW from Norway and trips, that's a 1,400 MW loss that the system must survive — larger than any single power station.

The GB grid's "secured standard" requires the system to withstand the loss of the largest single infeed without triggering customer disconnections. When interconnectors are running at full capacity, they often define this secured standard, forcing the system to carry more frequency response reserves.

When Interconnectors Help

Despite contributing no inertia, interconnectors provide significant benefits:

• Diversity of supply: When GB wind is low, French nuclear or Norwegian hydro can fill the gap
• Price arbitrage: Importing cheap off-peak power and exporting during high-price periods
• Emergency support: During severe shortfalls, interconnectors can rapidly increase imports
• Carbon reduction: Importing low-carbon electricity from Norway's hydro or France's nuclear reduces GB emissions

When Interconnectors Hurt Stability

The scenario that grid operators worry about most is high interconnector imports combined with low synchronous generation:

1. Mild, windy night — low demand, high wind, few gas plants running
2. Interconnectors importing heavily (cheap continental power)
3. System inertia is very low (few synchronous machines online)
4. If the largest interconnector trips → massive RoCoF event

This is precisely why the National Energy System Operator (NESO) monitors interconnector flows alongside inertia levels, and why GridHz tracks interconnector status as part of its largest credible loss detection.

What to Watch on the Dashboard

• Largest loss source: Check whether it's a generator or interconnector — interconnector trips tend to be instantaneous with no warning
• Total interconnector import: High imports + low inertia = elevated risk profile
• Frequency response margin: The sidebar shows whether Dynamic Containment reserves (DCL/DCH) exceed the largest credible loss
• Individual flows: The AI analysis panel can break down which interconnectors are importing or exporting and their impact on system stability