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Blackout investigation: National Grid ESO remains under scrutiny

Image: National Grid.

Image: National Grid.

Ofgem’s investigation into National Grid's Electricity System Operator (ESO) is to continue in light of the 9 August blackout, with the regulator recommending a review into the Security and Quality of Supply Standard (SQSS).

Whilst Ofgem hasn’t identified a direct causal link to suggest any failures by the ESO to meet its requirements caused the outage, it did identify issues that should be addressed by the ESO.

Ofgem has committed to continuing to review the ESO’s current application of the security standards it is required to meet. Alongside this review, the security standards themselves should also be reviewed, with Ofgem prepared to take the “necessary action” if the ESO is found to have failed to meet its requirements.

Ofgem will also continue to review the ESO’s application of the SQSS security requirements, to ensure the ESO’s judgements in securing the system appropriately balance the costs and risks to consumers. This review will be carried out alongside a review of the requirements themselves.

The ESO should also undertake a review, in consultation with the industry, into the SQSS requirements for holding reserve, response and system inertia, Ofgem said.

This should consider explicit impacts of distributed generation on the required level of security, the appropriateness of providing flexibility in the requirements for securing the network against risk events with a low likelihood and the costs and benefits of requiring the availability of more reserves to secure against simultaneous loss events.

The review should be carried out and modification proposals raised to the SQSS Panel by April 2020, which would provide appropriate channels for industry scrutiny and transparency and for an ultimate decision from Ofgem on any required changes.

The SQSS should also be updated periodically to reflect the changing system security risks and requirements.

Inertia and "poor performance" of frequency response

The ESO’s internal processes for estimating the impact of distributed generation on requirements don’t appear to be “sufficiently robust”, Ofgem said. This is given the marginal levels of system inertia and the “poor performance” of frequency response providers on the day of the blackout.

Ofgem criticised the response times of frequency providers in its investigation. Primary response providers, which are required to deliver a response in 10 seconds, under-delivered by 17%. Secondary providers, with a required response time of 30 seconds, under-delivered by 14%.

Mandatory response providers and commercial Fast Frequency Response providers of dynamic primary response, which are required to provide a continuous, proportional response, under-deliver by approximately 25%.

The ESO has initiated formal processes under the contracts in response to any under-delivery.

The availability of data between the DNOs and the ESO is “insufficient”, Ofgem said, with there being a lack of granular and accurate data available to ESO on distributed generator’s operational characteristics and performance in response to network faults.

Ofgem has detailed the action the ESO should take to address these issues:

  • The ESO should come forward with recommendations to improve the transparency of real time operational requirements and its holding of reserve, response and system inertia.
  • It should also review its procedures for holding balancing service providers to account for delivery of balancing services.
  • Ofgem is expecting the ESO to provide more visibility on how secure the system is and which services are being used to provide that security.

Compliance procedures

Ofgem also noted its concerns that the ESO allowed Hornsea One and Little Barford to reconnect to the transmission system without taking “adequate steps” to determine the root cause of the failures.

Hornsea One was reconnected following confirmation from the generator that the faulted equipment had been removed from service, but before the full root cause analysis had been completed.

The regulator also pointed to issues surrounding compliance of the generators with the Grid Code. The ESO was unaware of any potential compliance issues with Hornsea 1 or Little Barford ahead of the event.

However, the processes the ESO used to check compliance with the Grid Code are not robust enough, with the ESO relying significantly on self-certification by Hornsea One for its commissioning process, despite the complexity of the connection.

After Little Barford’s major refurbishment in 2011/12, the ESO also relied on RWE’s confirmation that the modifications had not impacted the generator’s compliance with the Grid Code requirements. No independent compliance testing or verification was carried out.

The ESO should therefore review and improve compliance testing and modelling processes for new and modified generations, in collaboration with generators and transmission owners. Progress should be reported to the E3C by April 2020.

National Grid ESO released a statement on social media website Twitter, which said it is “pleased” the report found no links between its actions and the blackout.

It pointed to many of the recommendations made by Ofgem being made by the ESO itself in its own report, as well as the ESO already beginning a review into the SQSS.

“We will continue to work with Ofgem, E3C and colleagues across the industry to address the issues raised and make sure that lessons are learned, and any changes made are in the best interests of the consumer."


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