Metering equipment at two National Grid Electricity Transmission substations that was connected in reverse caused errors in settlement totalling £117.5 million between December 2019 and February 2022, it has emerged. The errors will cause market participants to be over or under-charged, and settlements company Elexon said it had made over100 calls to market participants that would see a net impact of £250,000 or more. It is now contacting more market participants parties that will be affected by an error of £3000 or more.
Market monitoring raised questions over data at three so-called ‘grid supply point’ (GSP) groups, where power is fed between the high voltage national transmission grid and the low voltage network. Inspection at the two sites belonging to National Grid Electricity Transmission (NGET) found that in each case the polarity of one of several current transformers was reversed, meaning demand volumes were recorded as generation, (and in the case of _J, generation volumes recorded as demand; there was no generation at the site in _C).
At GSP Group_J (South Eastern GSP Group) 122GWh – valued at £17.5 million – was misrecorded between 4 December 2019 and 3 December 2021. At Group_C (London GSP Group) 798GWh – totalling £100 million – was misrecorded between 22 June 2021 and 23 February 2022. The error at the London GSP group will be corrected via normal settlement processes, which involve a series of settlement runs over a period of 14 months as data becomes available. But the error at the South Eastern GSP dates back beyond normal settlement processes and will be reconciled in extra settlement processes between now and August 2023.

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The errors mean there have been five Grid Supply Point (GSP) Metering errors in the last eight years, which Elexon says is equal to around 1.4% of the total number of GSP Meters. Registrants are responsible for their metering equipment.
The BSC Performance Assurance Board said it “has and will consider further preventative and remedial actions to stop such metering errors occurring in future”.
The errors may result in further inspection visits to meter sites.
Elexon has also been developing a machine-learning-based model that would provide alerts on unusual consumption patterns at individual GSP Metering Systems. But Elexon warned that its monitoring “is the last line of defence in detecting Settlement Errors and as such we want to ensure that it is as robust as possible”
It added, “this monitoring does not seek to detract from participants meeting their obligations under the BSC, such as the obligations on CVA Registrants to ensure Metering Equipment is kept in good working order, repair and condition such that energy volumes are recorded correctly.”

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