Offtake Metering Errors Stephen Skipp Asset Manager (Transmission and Storage)

Metering Systems Metering Systems must:- “Be installed, operated and maintained to the standard of a Reasonable and Prudent Operator” (UNC – OAD section D, paragraph 2.1.2) “Be capable of reading and set to read without systematic bias and within the Permitted Range” “Unless otherwise provided in the relevant Supplemental Agreement, the applicable industry standards and best practice recommendations set out in Annex D-2” (UNC – OAD section D, paragraph 2.2.1)

Metering Systems UNC – OAD Section D, Annex D-1 describes permitted uncertainty levels :- Instantaneous Volume Flow Rate +/- 1.0% CV +/- 0.1MJ/m3 (across range 35 – 44MJ/m 3 ) Pressure +/- 0.5bar (across range (0 – 85barg) Temperature +/ C (across range (0 – 40 0 C) Unless superseded by a Supplemental Agreement Instantaneous Volume Flow Rate +/- 2.0% (between 30% and 100% of maximum flow rate) +/- 3.5% (between 10% and 30% of maximum flow rate) CV +/- 0.14MJ/m 3 Pressure +/- 0.4% (across range (0 – 80barg) Temperature +/- 0.2% (across range (-10 – 40 0 C)

Supplemental Agreements Supplemental Agreement were agreed between National Grid Gas and the Distribution Networks at network sale Equipment complying with the general terms of the Supplemental Agreement is referred to as “Requisite Metering”. The following sites have Supplemental Agreements 6 sites in Scotland have volume flow and energy measurement 8 sites in Scotland have volume flow measurement with attributed CV 11 sites in Southern have volume flow and energy measurement 1 site in Scotland complies with Annex D-1

Liaison with National Grid Gas UKT Periodic review of emergency procedures (UNC – OAD section C, paragraph 2.3.6) National Grid Gas UKT, as the upstream party are entitled to:- Inspect measurement equipment (UNC – OAD section D, paragraph 2.4.1) Witness any validation (UNC – OAD section D, paragraph 3.1.4) Request exceptional validation (UNC – OAD section D, paragraph 3.3.1) Receive copies of records relating to installation, maintenance, testing, operation, calibration, setting and validation of measurement equipment (UNC – OAD section D, paragraph 7.2.1) Provision of maintenance plans (UNC – OAD section G, annex G-2) NGG UKT continue to determine daily CVs for each charging area for (SGN) (UNC – OAD section F, paragraph 4)

Liaison with National Grid Gas UKT Regular meetings Objectives: “To review offtake metering issues and ensure compliance with section ‘D’ of the Unified Network Code” “To promote best practice with the aim of preventing or minimising meter errors” Where errors are identified “To ensure that the appropriate processes are applied to rectify and account for the error” Frequency – approximately bi-monthly Agenda: Routine validations Validation witnessing Meter Errors Meter technology Meter records System Operation alarms

Identification of Meter Error Pro-active Annual Validation Routine validation “no less frequently than once every 12 months” (UNC – OAD section D, paragraph 3.2.1) Meter Audit Programme agreed with Ofgem Normally one per LDZ per annum Ofgem Gas Examiner CV / Metering Inspection Undertaken by Ofgem gas Examiner in conjunction with CV inspection Aim to complete one audit of every site per annum commencing April 2007 Re-active Fault report from System Operation Report from Operative during site visit Exceptional Validation requested by NGG

Meter Errors ‘Faults’ found since creation of SGN (June 2005):- SiteDatesCauseErrorTime to produce MER FarninghamJuly 1999 to June 2005Incorrect LGCF2.07% under15 months Braishfield AJune 2004 to July 2005Orifice plate contamination0.5% under7 months Winkfield SoPre 2000 to April 2007OMNI not configured to adjust downstream temperature to upstream conditions 0.059% over1 month BathgateDec’ber 2005 to June 2007Incorrect ‘K’ factor0.04% under1 month

Examples of potential meter errors Orifice plate / turbine meter condition Error assessed on extent of contamination Liquid contamination in impulse lines Error difficult to assess, action to prevent occurrence ‘K’ Factor error (turbine meters) Flow computer configuration error DWT local gravity correction factor not applied correctly

Analysis of meter errors Where incorrect data has been applied (e.g. LGCF) Identify reason for fault Identify duration of fault Initial calculation to identify likely scale of error Develop rules for control of missing, spurious data Extract 4 minute data for Inlet Pressure, Differential Pressures (orifice plate), Temperature, Volume Flow and Gas Composition from archive NB. Up to 360 packets of data per day Manipulate data into spreadsheet format Duplicate spreadsheets for corrected parameters Embed proven gas flow routines (e.g. GasVLe) into spreadsheets Run routines for original and corrected parameters Audit and review output

Summary of proposed changes Extend period permissible for production of MER Provide updates on progress of meter error calculations Initial notification after 14 days Subsequent updates every 14 days Information via SGN or third party website Obligation for Expert Determination of MER Where reconciliation required Expert selected from agreed list Report from Expert Determination to be circulated to relevant parties No change to current 642 / 643 process

Offtake Metering Errors Stephen Skipp Asset Manager (Transmission and Storage)