UNC Transmission Workstream 15 th June 2005

1. UNC Modification Proposal Number 0021 : Emergency Interruption Volume (EIV) Calculation Methodology UNC Transmission Workstream 15th June 2005

2. Introduction • UNC Modification Proposal 0021 is seeking to assign the volumes of gas, associated with potential Gas Deficit Emergency (GDE) Emergency Interruption actions undertaken by Transco NTS, to an effective trade (NBP title transfer) between Transco NTS and the relevant Shipper. • The introduction of an Emergency Interruption Volume (EIV) title trade would ensure that the Users’ imbalance positions prevailing at the time of the GDE are maintained. This paper seeks to define the methodology for calculating the EIV.

3. Emergency Interruption Volume (EIV) • Once Emergency Interruption has been initiated the volume of gas that would otherwise have been offtaken by the end-consumer cannot be known and therefore a proxy for the interrupted volume must be generated. • This is the Emergency Interruption Volume EIV. • A methodology is required that can calculate the EIV for any period of interruption

4. EIV Calculation Methodology • OPNs when available, represent the most accurate proxy for EIVs and can be used if interruption occurs within day. • OPNs (when available) have proven to be more accurate than Nominations • Nominations do not provide any information about within day flows and therefore may be inappropriate for the assessment of the EIV when Emergency interruption is initiated part way through a Gas Day. • Interruption Manager (IM) is used operationally for the DNs to assess the interrupted volume for non-OPN Supply Points. IM uses an algorithm based on historical consumption to quantify the interruption volume

5. OPN Supply Point Methodology

6. Non-OPN Supply Point Algorithm • Step 1 ~ Obtain a list of interrupted sites supply point ID’s and interruption start and end times for the chosen gas day. • Repeat the following steps (2-6) for each of these interrupted Supply Points • Step 2 ~ Identify whether this site was interrupted during the last 21 days and note which days were interrupted. • Step 3 ~ Calculate load… • If site was not interrupted on D-1, use demand from D-1 otherwise… • If site was not interrupted on D-7, use demand from D-7 otherwise… • If site was not interrupted on D-14, use demand from D-14 otherwise… • If site was not interrupted on D-21, use demand from D-21 otherwise… • Start at D-2 and work backwards to D-21 until a gas day is found where the site was not interrupted. • If all [21] days are interrupted, set estimate of interruption to zero. • Step 4 ~ Having worked out which day is to be used, get the load for this site for the chosen gas day. • Step 5 ~ Using the start time and restore time, only extract the portion of the day that the site was interrupted and copy the portion of the hourly loads needed. • Step 6 ~ Each supply point that was interrupted is noted along with its associated reason code (Transporter, Emergency, Shipper), Load type (for forecasting purposes), whether it is an NSL or not, which day was used for the replacement load (for validation/investigation) and 24 hourly load values.

7. Information Transfer • The proposal places an obligation on all relevant Shippers at multi-Shipper offtakes to provide the division method for the EIV for the relevant Transporter not more than [one] hour after interruption has been initiated. • The proposal places an obligation on all relevant Transporters to calculate the EIV for all relevant System Points and pass the data, aggregated by Shipper, on to Transco NTS as soon as is reasonably practical after interruption has been initiated.

8. Summary • The EIV will be calculated based on the volume implied by the OPN/SFN • The EIV will be allocated to Shippers based on the relevant agents method/data • When OPNs/SFNs are not available, the EIV will be based on consumption data from the most applicable historical day prior to interruption