1. NI Curtailment Risk Assessment Draft Update to PSASG 2004 Report 24 Sept 2007 Gordon Dobson-Mack 604-891-6004 Ellen Feng 604-891-6087

2. Outline 1.Background to PSASG Update report; 2.Highlights from report; 3.Example of Combining S>N and N>S Nomograms; 4.Recommendations from draft report

3. Update to PSASG 2004 Report Requested by many parties; Draft report – comments and improvements are welcome Attempts to present factual assessment of relative curtailment risk;

4. Highlights from draft report Curtailment risk lower than in 2004; 14 South to North N-1 operating conditions with curtailment risk 9 North to South N-1 operating conditions with curtailment risk Numerous examples of operating innovations Getting harder to schedule outages

5. Building a Combined 25F Nomogram Step 0: Define Terms Safe operating area: System remains within limits following the next worst contingency, regardless of PSA generation levels. Potentially safe operating area: Depending on PSA generation, the system may not remain within limits following the next worst contingency. Unsafe operating areas: System WILL NOT remain within limits following the next worst contingency, regardless of PSA generation levels. Danger area: blind spot: Depending on PSA generation levels, a specific contingency may cause a transmission element to exceed its limits. With current tools, the System Operators may not be aware of this risk.

6. Building a Combined 25F Nomogram Step 0: Define Terms Safe operating area: System remains within limits following the next worst contingency, regardless of PSA generation levels. Potentially safe operating area: Depending on PSA generation, the system may not remain within limits following the next worst contingency. Unsafe operating areas: System WILL NOT remain within limits following the next worst contingency, regardless of PSA generation levels. Danger area: blind spot: Depending on PSA generation levels, a specific contingency may cause a transmission element to exceed its limits. With current tools, the System Operators may not be aware of this risk.

7. Building a Combined 25F Nomogram Step 1: Import South-to-North Nomogram Tacoma-Covington #2 230kV line O/S Winter 2007 Heavy Loads Outage: 931 Temp: 25Fahrenheit Safe operating area Potentially safe operating area Unsafe operating areas Danger area: blind spot

8. Building a Combined 25F Nomogram Step 2: Evaluate the S>N Operating Areas Tacoma-Covington #2 230kV line O/S Winter 2007 Heavy Loads Outage: 931 Temp: 25Fahrenheit Safe operating area Potentially safe operating area Unsafe operating areas Danger area: blind spot

9. Building a Combined 25F Nomogram Step 3: Import & Invert North-to-South Nomogram Tacoma-Covington #2 230kV line O/S Winter 2007 Heavy Loads Outage: 931 Temp: 25Fahrenheit Safe operating area Potentially safe operating area Unsafe operating areas Danger area: blind spot

10. Building a Combined 25F Nomogram Step 4: Evaluate the N>S Operating Areas Tacoma-Covington #2 230kV line O/S Winter 2007 Heavy Loads Outage: 931 Temp: 25Fahrenheit Safe operating area Potentially safe operating area Unsafe operating areas Danger area: blind spot

11. Building a Combined 25F Nomogram Step 5: Combine & identify blind spots Tacoma-Covington #2 230kV line O/S Winter 2007 Heavy Loads Outage: 931 Temp: 25Fahrenheit Safe operating area Potentially safe operating area Unsafe operating areas Danger area: blind spot N-2: Echo Lk-Maple VL/Rocky Rch-ML contingency will overload COVINGTN TO CRESTON CKT 1

12. Building a Combined 25F Nomogram Step 6: Combine all Operating Areas Tacoma-Covington #2 230kV line O/S Winter 2007 Heavy Loads Outage: 931 Temp: 25Fahrenheit Safe operating area Potentially safe operating area Unsafe operating areas Danger area: blind spot

13. Recommendations from draft report Phase 1 Recommendations: 1.Develop an operating option for an Echo Lake-Maple Valley forced outage 2.Explore options for each High Risk and Very High Risk nomogram to reduce the curtailment risk 3.Review the Northern Intertie nomograms for negative operating points and implement operating practices to avoid these operating blind spots

14. Recommendations from draft report Phase 2 Recommendations: 4.Establish a Transmission Adequacy Guideline for the Puget Sound Area 5.Determine when the Puget Sound Area will need major system reinforcements to withstand All Lines in Service (N-0) and N-1 Operating Conditions. 6.Develop portfolios of projects that would ensure that the Puget Sound Area system is able to meet the newly established PSA Transmission Adequacy Guideline;

15. Recommendations from draft report Phase 3 Recommendations: 7.Investigate Nomogram study methodologies that treat Northern Intertie firm schedules as inputs, rather than outputs of the nomogram methodology.