To recommend approval of NPRR277 as revised by PRS
Vote tallies here reflect individual votes, not the weight of the votes by market segment.
Affirmative votes are not recorded in these vote tallies. For additional details on the voting
record, please consult the Recommendation or Action Report, or the official vote tally if
available, as posted in the key documents.
Sep 16, 2010
This Nodal Protocol Revision Request (NPRR) removes changes that were made to the Low Dispatch Limit (LDL) calculation within the Resource Limit Calculator (RLC) as part of NPRR119, Resource Limit Calculator. The language in this NPRR will ensure that a Resource’s Dispatch limits are calculated taking into consideration the Resource’s current net MW output and ramp rates. This NPRR also changes the Security-Constrained Economic Dispatch (SCED) Up and Down Ramp Rate calculation (SURAMP and SDRAMP) to reduce the amount of ramp rate that is reserved for Regulation Service.
The change to LDL calculation that was part of NPRR119 was intended to ensure that the Resources could not be dispatched at a level above the telemetered High Sustainable Limit (HSL). An unintended consequence of this change is that Security-Constrained Economic Dispatch (SCED) is able to set Base Points for a Resource that may not be attainable according to the ramp rates provided for that Resource. The ramp rates being used are either the Resource Asset Registration Form (RARF) ramp rates or those submitted via the Market Participant User Interface. If a large number of Resources are unable to follow Base Points, it may be difficult for ERCOT to match Load and generation and thus maintain frequency. This NPRR should help ensure that the all Base Points produced by SCED are attainable within the next five minutes.
In addition, this change will mitigate ERCOT’s sensitivity to the HSLs that are being telemetered by the Qualified Scheduling Entities (QSEs) and will place a larger degree of dependency on telemetered net MW and the ramp rates that have been provided for the Resource. This is in line with ERCOT’s RLC design approach which gives the telemetered net MW output highest priority in instances in which there are telemetry quality and/or accuracy issues.
These changes also ensure that at least some ramp capability is available from each Resource to SCED to economically resolve constraints.