Proposed ERCOT Nodal AGC Framework

Bob Green

Garland Power and Light Co.

January 3, 2007

-250

-180

-110

-40

30

100

170

240

310

380

450

520

590

660

730

800

4:30:00 4:35:00 4:40:00 4:45:00 4:50:00 4:55:00 5:00:00 5:05:00 5:10:00 5:15:00 5:20:00 5:25:00 5:30:00

59.80

59.82

59.84

59.86

59.88

59.90

59.92

59.94

59.96

59.98

60.00

60.02

60.04

60.06

60.08

60.10

REG RESP MILL HZ

8/11/06

MW Tripped

FREQ, REG, RESP, MILL ERCOT

845

Key Features

• SCED Base Points follow the daily load profile (5 minute update)

• REG and RRS deployments follow the frequency profile (4 second update)

• NSRS provides generation capacity to SCED based on operator judgment

Frequency will not be equal to 60 HZ because:

• The sum of the governor 60 HZ Set Points is not equal to the ERCOT load

• Real time load is different from the value dispatched in SCED

• Units are not following control base points

• Time lags and ramp limits in the AGC process

• Unit trip(s)

Problems with adding RRS deployment to the SCED input

• Will cause frequency overshoot and reverse direction REG

• Will probably cause units not bidding RRS to receive higher SCED Base Points

Changes required in the Nodal Protocols

• Delete 6.5.7.6.2.2 (9)

• Modify 8.1.2.4.2 (1)