Unaccounted for Gas (UAG) accounted for £57m and £50.86m commodity costs in 2012/13 and 2013/14 respectively. In 2013/14, this equated to ~£1.12/domestic gas householder/annum. Reduction in UAG has a holistic impact on all gas customers.
UAG is a function of meter error that is normally described in terms of measurement uncertainty. All measurement is commercially referenced in terms of meter uncertainty although during normal service operation, there is no requirement to establish absolute meter uncertainty as a part of the regular meter validation process.
National Grid Gas Transmission is responsible for the management of UAG, although it has limited ownership of the meter asset base. While it has visibility of all meter validations, these are provided in many forms (& sometimes media). The number (over 260) and range of sites make efficient analysis very difficult. This is also compounded by the timeliness of the validation data that makes tracking meter error very problematic.
National Grid has been developing numerous desk based UAG analytical techniques to assist in the day to day management of UAG. These have met with limited success, as any holistic analysis of UAG will include the error in the data. This pollution of the data makes individual site detection very unlikely unless the error is profoundly significant. However, it has long been realised that the annual meter validation data will contain valuable uncertainty information. Unfortunately due to widely differing validation approaches, albeit within the basic framework of the ME2 requirements (tolerances), makes accurate uncertainty and meter performance assessments difficult.
The Measurement Validation Assessment Tool (MVAT) will unify the entire meter validation process for gas transmission, distribution and all direct connected parties either at NTS or DN pressure tiers2. The software will standardise template for the validation process providing uncertainty and a set of gas composition calculations. Users will have a standard user interface (irrespective of platform) and will be provided a unique, secure data portal to which their reports will be uploaded and can then be analysed by National Grid.
MVAT is a unique offering, providing a meter validation capability as yet unavailable and provides the meter asset owner community a universal facility that will provide a level field in terms of data provision. National Grid will also utilize the data to better manage meter/UAG husbandry by incorporating the uncertainty analysis into the current UAG analysis tools. As MVAT will provide a true set of flow metrics (uncertainty v flow characteristics) it will be possible to begin to map ‘true meter uncertainty’ with observed UAG behavior. This has not been possible before as there has never been the opportunity to standardise the validation results on a common platform.
Note 2: Some low pressure (<15BarG) meter types (diaphragm, rotary) will not be included in the initial version of MVAP.
Benefits
It is proposed to evaluate the project in terms of the following success criteria:
1. Meter Uncertainty - The introduction of MVAT will provide a range of data currently unavailable to improve the management of UAG. The consistency of the validation approach will provide a clearer view of meter performance in real time and this is expected to encourage a more proactive re-basing of meter components. This re-trimming will be captured by the validation process and will result in meter systems with a reduced uncertainty range following validation.Success Criteria: - Increase of 50% in number of meters with improved measurement uncertainty following validation.
2. UAG Volumes (Energy) - MVAT will enable a greater control over the annual UAG volumes, particularly in relation to significant movements (bias) in behavior as a consequence of meter error. MVAT will help National Grid to maintain the current diminution of annual UAG levels over the last few years. Success Criteria: Continued reduction in UAG levels but MVAT assists in the determination of any measurement error identification.
