Diminished Unused Capacity (DUC)

Tuesday, February 02, 2016

Starting March 1, 2016, INSIDEtracc will begin automatically calculating the Diminished Unused Capacity (DUC) of PG&E’s California Gas Transmission system.

What is DUC?

A pipeline’s capacity is set based on its maximum calculated flow potential over a 24-hour period.

For example, CGT might be showing a maximum Redwood Capacity of 2,000 MMcf for a particular gas day. Let’s say that no one nominated anything on Redwood for the Timely, Evening, and ID1 cycles. If one shipper wanted to nominate the whole 2,000 MMcf on the ID2 cycle, it would be impossible for CGT to physically flow that volume in the remaining 12 hours of the gas day. Although this capacity went “unused,” the ability to use the full capacity has been “diminished” because there are only 12 hours left in the day to make it physically flow.

Why is DUC Being Automated?

There are several reasons why we’re automating the calculation of DUC:

  • Automation will become especially important as we prepare for the addition of this year’s 5th nomination cycle, Intraday 3. Since the additional cycle will add complexity to our processes, automating DUC allows us to tighten up internal workflows to better serve you.
  • Automation will help more accurately determine which nominations are physically capable of flowing.
  • Interconnecting pipelines also calculate capacity utilizing DUC. By implementing automation, we will be better at matching up with other pipelines’ confirmations of nominations.
  • Automating DUC will make sure we remain compliant with Gas Rule 21, Section B.3.b.2.

What Does DUC Mean for You?

DUC can impact customers who submit late-day nominations. CGT recommends submitting nominations on the earliest cycle possible in order to help reduce your risk of running into DUC reductions.

If you have any questions about DUC, please do not hesitate to reach out to the CGT Gas Scheduling team or your CGT Account Manager.

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