Spinning Reserve from Load Consideration of a Trial at Xcel Energy’s Cabin Creek Station

1. Spinning Reserve from LoadConsideration of a Trial at Xcel Energy’s Cabin Creek Station Presentation to CMOPS January 7, 2005 John Kueck ORNL Brendan Kirby ORNL

2. Responsive Load Is Different than Spinning Reserve from Generators, Spinning Generators Provide: • Inertia – Spinning generation opposes changes in speed • Voltage Support with the Exciter • Speed droop regulation with the Governor • The PSS provides Power System Stabilization • Generation is responsive to AGC • Rapid Reserve Supply – This is only service that we are replacing with responsive load.

3. But, Load Has Some Advantages Too! • Load curtailment provides a reduction in real and reactive system losses. • Load curtailment provides a reduction in real and reactive system load. • Load drop could be done in urban areas and other needed locations. • Load drop reduces transmission flow, vs. spin which often increases flow. You can have a bigger impact with the same amount of load than with generation. • With small loads, we may be able to build in a frequency responsive droop characteristic. • The total response is faster, generation can take 10 minutes to ramp up.

4. Xcel Energy Is Considering a Trial of Spinning Reserve from Load • We hope to include your questions today in the analysis for this trial. • At the Vancouver CMOPS meeting, there was a request for a study on the effect of inertia and the frequency response to the provision of spin from load. • An analysis has been performed by WECC on the concept and we will present those findings now.

5. WECC Has Done Some Educational Analysis on System Response to Load, the Contingency is Loss of Palo Verde 1 • Case A is the normal base case simulation. • In Case B, All governors are blocked from responding. • Case C is the same as B, except Helms trips at 59.95 Hz Analysis done by Donald Davies, WECC

6. WECC Has Done Some Educational Analysis on System Response to Load, the Contingency is Loss of Palo Verde 1 • In Case B, even with all governors blocked, the frequency goes down to the under frequency trip point, 59.65, and then comes back up due to the load shed and stabilizes due to the frequency response characteristic of the load.Case C is the same as B, except Helms trips at 59.95 Hz Analysis done by Donald Davies, WECC

7. WECC Analysis Continued: the Contingency is Loss of Palo Verde 1 • Case D has all governors blocked, but added 300 MW of governor response. • Case E, all governors blocked, units have been rescheduled to remove 300 MW of spinning reserves in northern California, Helms trips at 59.95 • Case F, normal governors again, but 300 MW of spin has been removed and one Helms pump trips at 59.95 Analysis done by Donald Davies, WECC

8. WECC Analysis Continued: the Contingency is Loss of Palo Verde 1 • Case A is the normal base case simulation. • Case F, normal governors again, but 300 MW of spin has been removed and one Helms pump trips at 59.95 – A better freq. response than the normal base case. Analysis done by Donald Davies, WECC

9. Significant Analysis Findings - Inertia • Plots C and E are essentially the same line, but 1686 MVA of generation had been turned off for E, or about 5,000 MW Seconds, this amount of inertia has negligible impact on frequency response. Analysis done by Donald Davies, WECC

10. Proposed Xcel Energy Trial • The study done by WECC on the use of the Helms pump to replace 300 MW of spinning reserve provides an indication that the concept is viable. • Xcel Energy is considering a one year trial of the Cabin Creek pump to provide spinning reserve. The trial will be discontinued if at any time there is a hint of a reliability concern. • Xcel Energy is presently performing analysis to examine the details of providing this service from Cabin Creek, and would like to include CMOPS questions in this analysis.

11. Some of the questions that will be addressed are: • At night, during light load conditions, would the load drop create a voltage regulation problem? • How fast could Cabin Creek ramp down in power level with no equipment degradation? • What would the frequency trip setpoint be? Would there be one for each pump? • A detailed test plan is being developed, it will answer the above questions and discuss the method for monitoring performance

12. Other Questions • Will Xcel be required to obtain a waiver to RMS for the trial? • What particular concerns and questions should be addressed in the Xcel analysis in preparation for the trial? • Is there a need to create a Working Group to study the concept of spinning reserve from load in general? There were volunteers at the MORC meeting.

14. Extra Slides

15. Questions and Answers Contd. • Aren’t there timing issues for the load response, when is it initiated, actually dropped, and restored? This question is being investigated, load response could occur very quickly, in a few seconds, reclosing effects are being tested this summer on air conditioning loads . • Enrolling load in this program will take load from the frequency responsive load safety net. Load will be enrolled under new contracts, the loads will have to be willing to be responsive to the service. We anticipate that new loads would become available.

16. What About Inertia, the SCIT Nomogram? • The SCIT nomogram restricts imports into Southern California as a function of imported power flow. Inertia is not the major factor in setting the limits, the factor is likely exciter response. The inertia change is a secondary effect that we feel certain has been shown to be negligible by studies.

17. Questions and Answers on Spin from Load • Doesn’t spin from generators provide voltage support? Yes, but dropping load does help voltage, and this effect will be enhanced by dropping load in load centers. • Spin from generation provides a frequency responsive droop characteristic, but load drop will be lumpy. Load drop could be incremental with frequency droop. Also, the speed droop characteristic only provides for the droop characteristic change in generation, the entire reserve of load could be brought on before reaching 59.7 Hz.

18. Flow Issues Contd. • There is plenty of governor response in the Northwest with the hydro plants, but this is limited in Southern California. • The Southern California thermal units are being operated close to their limits. • With a generation contingency South of Malin, there is heavy flow to the Southbound through the COI because the governor response is in the North. • Responsive load in the South would help both the rapid reserves and the voltage issue.

19. Other Concerns that Need to Be Addressed/Studies • What are the needs with restoration, cold load pick up, especially with air conditioning • How long do the loads have to be off, 30 minutes, 2 hours? • What are the contractural concerns, each CA must respond to frequency decay caused by contingencies within the control area. Also, ACE deviations are biased by frequency, and this must be corrected as they are now for AGC action. • There is a limit as to how much spinning reserve can be replaced by responsive load because of the unique services it provides, we will have to determine this limit through case studies.