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Offtake Metering Errors

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)

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Offtake Metering Errors

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

  2. 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)

  3. 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– 44MJ/m3) • Pressure +/- 0.5bar (across range (0 – 85barg) • Temperature +/- 1.00C (across range (0 – 400C) • Unless superseded by a Supplemental Agreement • Instantaneous Volume Flow Rate • +/- 2.0% (between 30% and 100% of maximum flow rate) • +/- 3.5% (between 10% and 30% of maximum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/m3 • Pressure +/- 0.4% (across range (0 – 80barg) • Temperature +/- 0.2% (across range (-10 – 400C)

  4. 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

  5. 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)

  6. 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: • Meter technology • Meter records • System Operation alarms • Routine validations • Validation witnessing • Meter Errors

  7. 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

  8. Meter Errors ‘Faults’ found since creation of SGN (June 2005):-

  9. 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

  10. 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

  11. 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

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

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