IRRs behind GTCs follow basepoints (NPRR1111/SCR819)

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By STEVE REEDY

The Gist

SCR819/NPRR1111 will require Intermittent Renewable Resources (IIRs) to follow their base points if they are behind a Generic Transmission Constraint that is in danger of being violated. It is currently tabled at PRS. As ERCOT puts it, “With each SCED Base Point sent by ERCOT to the Qualified Scheduling Entity (QSE) representing an IRR, ERCOT also sends a curtailment flag (ON=TRUE=1; OFF=FALSE=0), hereafter referred to as the SCED Base Point Below HDL (“SBBH”), to indicate whether the SCED Base Point is less than the HDL that was used in the SCED calculation (refer to paragraph (1)(d) of Nodal Protocols Section 6.5.7.4, Base Points). ERCOT systems set the SBBH flag to TRUE when the SCED Base Point is below the IRR’s HDL used in SCED. While the SBBH flag is TRUE, the IRR is required not to exceed the SCED Base Point Dispatch Instructions.

For those units of IRRs behind a GTC which are not being curtailed by SCED, i.e., the SBBH flag is FALSE, they are permitted to produce their power at the maximum potential while ignoring SCED Base Points. This behavior may lead to an undesirable increase in GTC power flow due to a sudden ramp up of power injected by those unconstrained IRRs. From a GTL-management perspective, a larger margin or a lower discount factor (reliability limit) are required in the Transmission Constraint Manager to accommodate those unaccounted deviations from SCED Base Points.

This SCR will modify the ERCOT Energy Management System (EMS) such that all IRR units behind a GTC with a shift factor greater than 2% on the corresponding GTC will receive an instruction not to exceed their SCED Base Point when the GTC loading is above a threshold and the GTC constraint is activated and binding in SCED.”. That is to say, this will allow ERCOT to control IRR’s behind GTCs so that a sudden gust of wind doesn’t blow the flow of the GTC over the limit. This will allow ERCOT to operate the GTCs with less of a cushion and get more energy out of resources behind GTCs.