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.

The graphs may take a couple of seconds to load. To expand the graphs, tap the double-headed arrow in the bottom right corner of the graph.

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.


Transmission Loss Multipliers (TLMs) continue to be volatile in 2024 as it was the case in 2023.

The lower TLMs are usually seen in GSP Group _P due to the high amount of generation in North Scotland feeding through into the TLM calculations.

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.


Week 51 in 2023 shows the highest peak seen so far. Given previous weeks with high losses have fallen once more accurate data is received, it is expected this week will continue that trend.


Click on the X next to any of the icons to replace them with a short-cut link to the page you are currently on or search for a specific page.