Responsive Reserve Service Deliverability Review

September 15, 2011

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IntroductionResponsive Reserve Service Capacity as it

relates to congestion and its deliverability.Responsive Reserve Capacity during the

February 2nd EEA event.The potential affect of Responsive Reserve

Service capacity that is not frequency responsive.

Responsive Reserve Service allocation limits on a single Resource, is the 20% capacity limit correct?

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Congested Responsive Reserve Service CapacitySCED will utilize congested RRS capacity last.Congested RRS capacity will continue to provide

Primary Frequency Response even while congested.Governor In-service and free to respond to all

frequency deviations outside Governor Dead-Band.During EEA-2A and 2B, RRS Capacity on Generators

will be utilized to maintain frequency at 60 Hz.During EEA- 3, RRS Capacity on Generators will be

utilized to maintain frequency above 59.80 Hz.

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Percent of 5 minute intervals in a month when transmission constraint was affecting # of resources carrying RRS

Month-Year AVG Number of Resources carrying RRS

Max Number of Resources carrying RRS

Min Number of Resources carrying RRS

1-10 Resources 10-20 Resources

20-30 Resources

Greater than 30 Resources

sum

Dec-10 31 44 (1.20% intervals >35)

13 (0.067%<20) 12.34% 5.42% 10.21% 7.59% 35.56%

Jan-11 29 39(1.63% intervals >35)

15 (0.201%<20) 17.70% 3.90% 10.79% 2.48% 34.87%

Feb-11 44 85 (1.88% intervals >80)

23 (0.174%<25) 18.97% 2.88% 9.54% 14.99% 46.37%

Mar-11 37 48 (24.30% intervals > 40)

23 (5.63% < 30) 8.20% 1.11% 1.38% 11.04% 21.73%

Apr-11 37 54 (4.98% intervals > 45)

23 (3.34% < 30) 33.90% 6.31% 7.68% 7.22% 55.11%

May-11 34 47 (3.93% intervals > 40)

19 (0.0112% < 25)

26.72% 10.62% 13.80% 9.01% 60.15%

Slide provided by ERCOT, Constrained = Resource LMP more than $0.50 below system lambda.

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1. 5 minute sampled data

2. Telemetered Responsibility used to determine number of

Resources carrying RRS

3. 1% duration generally converts to roughly ninety 5-minute

intervals (31 days month)

4. The number of resources carrying RRS may include up to 13

resources in Synchronous Condenser (Hydro)5

During the February 2nd EEA event.

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59.50

59.52

59.54

59.56

59.58

59.60

59.62

59.64

59.66

59.68

59.70

59.72

59.74

59.76

59.78

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

5:35 5:40 5:45 5:50 5:55 6:00 6:05 6:10 6:15 6:20 6:25 6:30 6:35

Hz

0

50

100

150

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

1100

1150

1200

1250

1300

1350

1400

1450

1500

MW

Frequency ERCOT Total Physical Reserve

Wednesday, February 02, 2011

Frequency 59.80 Hz

Physical Reserve = 850 MW

Physical Reserve = 450 MW

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During Short Supply PeriodsResponsive Reserve Service capacity can

decrease to very low levels during EEA 2 and 3 events.

August 4 EEA 2B event, RRS capacity decreased to levels just below 1000 MW.

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That is not frequency responsive.

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RRS Capacity that is not Frequency ResponsiveIf allowed, increases risk of UFLS significantly.If constrained, non-frequency responsive

capacity may never be utilized.With grid Primary Frequency Response

depending totally on Load Dampening, frequency would be extremely sensitive to any imbalance. (If all RRS was not frequency responsive).

Frequency could reach 59.300 Hz before capacity could be utilized by SCED and waiting on delivery. (Ten minute product vs. frequency responsive product).

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Load RRS Gen Total Load Dampening RRS Capacity Resource LossDampening PFR PFR Contribution Contribution to ReachMW/0.1 Hz MW/0.1 Hz MW/0.1 Hz MW MW* 59.400 Hz

Summer -166 -191 -357 996 1000 1996 MWWinter -73 -191 -264 438 1000 1438 MW

Summer -166 0 -166 996 0 996 MWWinter -73 0 -73 438 0 438 MW

*MW less than normal minimum 1150 MW on Generators due to SCED dispatching some of the capacity as energy.If RR Ancillary Service is not required to be frequency responsive.

Recent Operation During EEA Step 2A and 2B Emphasizes An

Important DifferenceRegulation Up Service was fully deployed.Load Resources were fully deployed.SCED Up Capacity was limited to the

capacity of un-deployed Responsive Reserve Service from Generators.

MW loss size assumes a starting frequency of 60.000 Hz. 11

SummaryResponsive Reserve Service capacity that

does not respond to changes in frequency, increases the risk that a relatively small Resource trip during short supply events will trip UFLS.

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Deliverability during sudden, extreme events (May 15, 2003).

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20% Capacity Limit per ResourceThe Governor of a Resource will deploy 20%

of the capacity of a Resource if frequency deviates -0.600 Hz plus the Governor Dead-Band.At 59.364* Hz, the Governor will deploy 20% of

the capacity of a Resource with a 5% Droop setting.

Even if fully constrained by SCED, full RRS should be deployed by the Governor before the first stage of UFLS, 59.300 Hz, is reached.

* Originally the RRS was intended to protect 59.40 Hz and did not include Governor Deadband. Using the maximum Governor Deadband of 0.036 Hz this number now comes out to be 59.364 Hz.

Resource Performance May 15, 2003May 15, 2003 loss of 3434 MW and 59.29 Hz Point

C and 59.46 Hz Point B. During the first minute of the event:16 Steam units responded with average 0.655 P.U.

performance. (65.5 % of expected response)13 Combustion turbines responded with average

0.660 P.U. performance. (66% of expected response)Generators responding correctly provided 14% of

their capacity on average in less than one minute. 5 steam units provided 18% or greater. 2 combustion turbines provided 18% or greater. 5 combustion turbines provided 16% or greater. 2 steam units provided 16% or greater.

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SummaryIs the 20% allocation limit correct for

maximum deliverability during sudden, extreme events?

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