Gas Transmission Networks
Unaccounted for Gas (UAG) accounted for £51m and £43m commodity costs in 2013/14 and 2014/15 respectively. Any reduction in UAG has a holistic impact for all UK gas consumers.National Grid’s UAG management is multi faceted, involving both site based witnessing and the use of desktop analysis models. Most of these models are based on regression and energy use metrics and it has long been realised, that as these techniques have to analyse daily UAG volumes, they are not of sufficient sensitivity to indicate anything but the most gross errors. Currently, daily average UAG is 0.09% of NTS throughput, which corresponds to all measurement systems operating within their contractual obligations (NExA, SCA, NEA) at a holistic bias level (+/- 0.1%). Measurement uncertainty is a measure of meter behaviour about a mean and as NTS UAG is determined from cumulative daily site total flows, individual flow errors can offset. This makes tracking individual site behaviour problematic due to overall data ‘noise’ within the UAG calculation.
It is proposed to explore alternative mathematical techniques to develop a set of robust models for the determination and monitoring of biases in UAG data. The techniques will be refined to provide a model set that can allow time efficient data analysis, which allows more individual site measurement issue can be addressed with in the commercially defined close out periods.
To develop a comprehensive set of mathematical models to assist in the management of UAG through:
1. The development of a robust suite of UAG baseline (tolerance) models.
2. The development of a suite of mathematical analysis techniques to assist in the on-going management of UAG.
It is proposed to evaluate the programme in terms of the following success criteria:
- Baseline Determination:- The introduction of a baseline metric into the standard UAG management process will greatly assist in the assessment of the effectiveness of the control and monitoring processes being employed. This should enable the UAG management techniques to be refined and targeted in specific areas greatly improving response and holistic management with all stakeholders.
- Mathematical Analysis Techniques:- The mathematical techniques will build on the baseline analysis to provide a suite of tools and models that will be embedded into National Grid’s UAG management processes.