An interconnected future
August 18, 2022
Dr. Luke Livermore

The energy crisis engulfing Europe has placed HVDC interconnectors in the spotlight like never before. But what is the impact of such a high penetration of power electronics into the U.K.’s electricity network in such a short span of time?

Interconnectors between countries to integrate vast offshore wind farms are key to the U.K.’s path to net zero. They provide a conduit to connect areas of plentiful renewable energy resources to major load centers. The U.K. Government’s ambition to deliver at least 18GW of interconnection capacity by 2030 confirms the elevated pace of change.

The E.U. is equally committed to interconnectors encouraging countries to install capacity to allow at least 15% of electricity produced within its territory to be exported to neighboring countries. This is in addition to the Project of Common Interest (PCI) nomination to large interconnector projects.

Declining inertia

An inevitable part of the transition from conventional fossil, nuclear and hydro-powered generators to inverter-based resources linked to HVDC interconnectors is a significant drop in system inertia.

Large rotating turbines found in traditional thermal power generators resist sudden changes in frequency. In a way, slowing or stopping the turbines’ rotating mass is like trying to turn an oil tanker; it takes time. However, this inertia helps the stability of the network by buying time to rebalance the generation and load.

The converter stations at either end of the interconnector have no such rotating turbine. Instead, transistor-based power electronics rapidly generate A.C. voltage waveforms, converting D.C. power in the high-capacity cable into A.C. power. Their behavior is more characterized by a speedboat. It may not have the inertia of the oil tanker but its speed of response means that within milliseconds course correction can be applied to support the A.C. frequency. This is known as ‘synthetic inertia’ or ‘fast frequency response.’

Action on interaction

With the proliferation of interconnectors within the U.K. gaining momentum, certain parts of the U.K. network have become – or will become – ‘hubs’ where converter stations are sited in close proximity with one another. In practical terms, careful coordination is required to ensure no adverse interactions between converters. The nature of these interactions can be at sub- or super-synchronous frequencies due to transient events or fault events. Therefore, the conscientious interconnector owner/operator needs to perform a suite of simulation studies to garner a comprehensive understanding of the consequences of connection.

Navigating to a highly connected future

The future is bright despite the challenges and the changing way the U.K. network will need to adapt to new and more complex interconnectors. With careful planning, the benefits of sharing renewable generation, increased energy security and downward energy price pressure can be realized while also maintaining the safety and security of the U.K. network. What is needed are efficient connection rules and a collaborative approach from interconnector owners, Original Equipment Manufacturers (OEMs) and Transmission System Operators (TSOs) to quickly realize this future.

Find out more about PSC’s HVDC and Power Networks capabilities.