Transmission Losses data from the Trading Operations Report


The page below details highlighted Transmission Losses data from the previous month. This data is acquired from BSC Agents and inputted to the Trading Operation Monitoring Analysis System (TOMAS) database.

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Daily Average Offtaking TLM

The chart below shows the daily average Offtaking TLM based on the II Run or later. Following the implementation of BSC Modification P350 ‘Introduction of a seasonal Zonal Transmission Losses scheme’ on 1 April 2018, TLMs vary on a regional basis. Before P350, there was only one offtaking TLM value per settlement period which was always greater than one to allocate Transmission Losses to all Offtaking BMUs uniformly. Since P350 there are now 14 offtaking TLM values per settlement period, one per GSP Group. Some of the offtaking TLMs might now be smaller than one, signifying that consumption in that region could reduce Transmission Losses.


TLMs continue to be volatile in 2023, with peaks and troughs continuing to be investigated – especially around 19 August 2023 and 24 September 2023. Note the peak reported last month on 15 September 2023 has now been corrected, with TLMs moving back to a more expected level.

The lower TLMs seen in GSP Group _P are likely to be due to the high amount of generation in North Scotland feeding through into the TLM calculations, and the known issue with a wind farm as mentioned in the GCF commentary above.

Average Weekly Transmission Losses

This chart shows the average weekly transmission losses for the current calendar year (to date) and the previous three calendar years.

‟Week 1‟ shown on the x-axis refers to the first week of January; ‟Week 2‟ refers to the second week and so on. The chart uses data from the latest run type available, from Settlement Final (SF) onwards.

This chart shows the trend of transmission losses and enables a comparison against the last three years for identification of any patterns, increases or decreases that may require investigation.


The higher-than-expected weekly average Transmission Losses seen in Q4 2022 and January 2023 had subsided; however, new peak has been seen in week 33 and week 39.

As mentioned last month, the peak seen in week 30 has reduced, following more accurate data being received as part of the settlement process; we expect something similar to happen for these weeks when more accurate data is received.


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