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  • Unaccounted for Gas (UAG)

  • One of the key aspects of our management of the NTS is our role as the Shrinkage Provider. This role is defined in the Uniform Network Code (UNC) and places a responsibility on National Grid to forecast, procure and manage NTS Shrinkage appropriately on behalf of all system users.
    NTS Shrinkage is made up of three components:
    1. Compressor Fuel Use (CFU), which is the total energy used by the compressors which help to maintain pressure and flow in the NTS. CFU is made up of fuel gas used for the gas turbine powered compressors (Own use Gas, or OUG) and energy used by the electric driven compressors;
    2. Unbilled Energy, normally referred to as Calorific Value Shrinkage (CVS), which is the difference between delivered and billed energy of a charging zone as a consequence of applying the Flow Weighted Average Calorific Value (FWACV) process in accordance with the Gas (Calculation of Thermal Energy) Regulations 1996; and
    3. NTS Unaccounted for Gas (NTS UAG), which is the gas which is lost or otherwise not accounted for as offtaken from the NTS. NTS UAG is considered to be the consequence of data and or meter error and is thus a relatively complex component of shrinkage, involving not only the mechanical behaviour of high pressure metering systems but statistical variations in their operation.

    Daily UAG data has been published on the National Grid website since October 2012. Weekly updates are made to this information and cover the period from 1 March 2007 up to 7 days previous. Due to the process of data close out (Day plus 5 and Month plus 15) the recent values are subject to change and is available via the following link:

  • Daily UAG to 10 Nov 2017
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  • National Grid regularly reports on our activity to investigate potential causes of UAG, the most recent report is available below. This report covers the latest UAG trends and provides updates of National Grid's data analysis and meter validation activities.

    October 2017

    The previous reports are available via the following links:

    April 2017

    October 2016

    April 2016

    October 2015

     April 2015  

    October 2014

    April 2014

    October 2013

    May 2013

    February 2013

    July 2012


    These reports and activity discharge National Grid Gas's (NGG's) responsibilities under Special Condition 8E (from 1 April 2013)

     "Requirement to undertake UAG Projects to investigate the causes of Unaccounted for Gas (UAG)".


    National Grid are developing a tablet app to aid Meter Validations (ME2) and thus improve the management of UAG for more info click here. 

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