This excerpt taken from the PCG 10-K filed Feb 18, 2005.
Path 15 Real-Time South-to-North Curtailment Priorities1/
Note: This document is intended to explain the procedures for calculation and allocation of Available Transfer Capacity (ATC) over Path 15 pursuant to the Federal Energy Regulatory Commission's May 22, 2002 order in Docket ER99-1770-001 (99 FERC ¶ 61,212). It should not be interpreted in any way to modify Exhibit B-1 of the Transmission Control Agreement.
California ISO calculation of Path 15 ATC in the Day Ahead and Hour Ahead Markets (largely described in Exhibit B-1):
Allocation of ATC on Path 15 in real-time, i.e. calculate ETC available rights and curtailments based on applicable priorities (largely described in Exhibit B-1 and Attachment A to Exhibit B-1):
Thus, in real time, NFU access to transmission capacity over Path 15 has two levels of priority:
Second, as any capacity that remains after subtracting from OTC the actual schedules for Priority 1-3 ETCs and the NFU amount above.
However, operationally the ISO does not allocate particular NFU schedules to a particular priority but rather treats all NFU schedules as a single block. The following example illustrates how this occurs:
Assume that OTC over Path 15 is 2,500 MW in a given hour and that there is no Unscheduled Flow. Assume that there are 800 MW of Priority 1 ETC actual schedules, 1,000 MW of PG&E Must Take Encumbrance, 200 MW of lower priority ETC actual schedules, and 1,500 MW of NFU. This NFU amount, as described above, uses the 1,000 MW of PG&E Must Take Encumbrance and the amount of capability remaining after accommodating the lower priority ETC schedules. Assume that Path 15 is derated to 2,000 MW. In this example, no ETC curtailment is indicated, thus the ISO must take actions to reduce the flow. The ISO would use Adjustment Bids and Supplemental Energy bids in the BEEP stack to attempt to accommodate the transactions without curtailing any of the NFU schedules. Assume that after bids in the BEEP stack are exhausted, 1,200 MW of NFU remain on Path 15 and curtailments are required (this occurrence is rare). If feasible within the time available to manage the Path derating, the 1,200 MW of NFU would be curtailed on a pro-rata basis to result in NFU of 1,000 MW. Assume that Path 15 is further derated to 1,000 MW and that all bids in the BEEP stack remain exhausted. If feasible within the time available to manage the Path derating, the 1,000 MW of NFU (the amount that is using the priority rights equal to the amount of the PG&E Must Take Encumbrance) would be curtailed on a pro-rata basis to result in NFU of 200 MW and the lower priority ETC schedules would be curtailed to 0 MW. Note: Priority 1 ETC rights are determined on the basis of the Path 15 OTC, and only curtailed if the Priority 1 ETC rights holder's schedule exceeds its contract right or entitlement amount.