Fire at an HVDC converter station leads to site evacuation and loss of interconnector capacity

In September 2021, a fire broke out at a high voltage direct current converter station in the United Kingdom serving a subsea interconnector to continental Europe. The site was evacuated and emergency services attended. The link is arranged as two poles of equal rating, and one pole was already out of service on a planned maintenance outage before the fire, so available capacity had already been reduced by half. Following the fire, the status of the affected pole was changed on a European transparency platform from a planned outage to an unplanned outage, and reported flows on the link fell to zero. The event coincided with tight system conditions, and day ahead prices for the immediate evening peak period rose to over 2,500 pounds per MWh. The national system operator stated that sufficient operating margin was forecast for that evening's peak demand period. No injuries to personnel were reported and the site evacuation was completed without incident.

Public statements at the time emphasised the safety of staff, emergency responders and local residents as the priority. The cause was the subject of a formal investigation and was not disclosed in the public reporting available at the time of writing, so no causal factors are recorded here. Reporting noted only that one pole of the link was already out of service for planned maintenance when the fire occurred.

1. Treat converter halls as concentrated electrical and thermal energy risks and confirm that automatic detection, fixed suppression and fire separation between converter halls, auxiliary buildings and control rooms are in place and tested.
2. Review contingency arrangements for the period when one pole of a bipole link is on planned outage, so that the loss of the remaining capacity is covered by an agreed operational response rather than by assumption.
3. Make sure site evacuation and emergency plans set out the high voltage de-energisation and earthing sequence for direct current plant, which can take longer than for alternating current switchyards, and share that sequence with the local fire and rescue service in advance.
4. Assume that any change in interconnector availability will appear on public transparency platforms within minutes, and prepare holding statements and internal notification routes accordingly.
5. Plan for a return to service that includes extensive electrical testing and recommissioning, so that outage duration estimates issued to the market reflect more than the immediate fire response.
6. Record the market conditions at the time of an outage, since the loss of a large import route during tight margin periods has a visible effect on day ahead prices and on stakeholder interest in the event.

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