1. 1 Sunrise Powerlink and Southwest Powerlink Reliability Performance Evaluation Double Line Outage Probability Analysis March 6, 2008

2. 2 RPEWG and RS Recommendation After reviewing SDG&Es report, both the RS and RPEWG recommend that the proposed path (4 miles – 12 towers) for the Sunrise Powerlink and Southwest Powerlink double line outage analysis be approved for the category upgrade to Category D with cascading allowed.

3. 3 Step 1: Project (Facility) Description SDG&E has proposed a new 500 kV transmission line called the Sunrise Powerlink (SRPL) that will connect the existing Imperial Valley substation, near El Centro, California to a new Central substation located in a central part of San Diego County. The proposed path for the Sunrise Powerlink would be in the same right of way as the Imperial Valley - Miguel line for approximately 4 miles. This route would contain approximately 12 towers. Step 1Step 2Step 3Step 4Step 5Step 6Step 7

4. 4 Proposed and Alternative Paths Proposed Path – approximately 4 miles Alternative Path – approximately 36 miles

5. 5 12 Tower Structures Step 1Step 2Step 3Step 4Step 5Step 6Step 7 Tower 50281Tower 50280Tower 50279 Tower 50273Tower 50276Tower 50274Tower 50275 Tower 50277Tower 50278 Tower 50272Tower 50271Tower 50270

6. 6 Step 2: Outage Database – The Sample SWPL is SDG&Es only 500 kV transmission line, therefore outage data was collected on the Imperial Valley - Miguel portion of SWPL. With thirteen years of outage data (1995 - 2007) available, SDG&E concluded that of the 44 forced outages on the Imperial Valley - Miguel line there was only one event that occurred on the proposed shared right of way during these years. SDG&E determined that using historical 500 kV data from the Palo Verde Hub to North Gila Performance Category Upgrade Request report by Arizona Public Service (APS) would be appropriate. Step 1Step 2Step 3Step 4Step 5Step 6Step 7

7. 7 Step 3: Zero Events - Corrected MTBF MTBF is 928 years P T, P L, and P H are calculated using zero(0) events. SDG&E feels that after reviewing the data from the Robust Line Design, the MTBF will tend towards this value. Step 1Step 2Step 3Step 4Step 5Step 6Step 7

8. 8 One Event - Corrected MTBF MTBF is 21 years P T, P L, and P H are calculated using one (1) event. The reason that there are two sets of values for the MTBF, is because there is not enough data to calculate definite values. Step 1Step 2Step 3Step 4Step 5Step 6Step 7

9. 9 Step 4: Risk Factor Summary RiskRisk Factor R1Fire affecting both linesLow Risk R2One tower falling into another lineLow Risk R3Conductor from one line being dragged into another lineLow Risk R4Lightening strikes tripping both linesLow Risk R5Aircraft flying into both linesLow Risk R6Station related problems resulting in loss of two lines for a single eventLow Risk R7Natural disastersLow Risk R8Loss of two lines due to an overhead crossingLow Risk R9Loss of two lines due to vandalism/malicious actsLow Risk R10Flashover to vegetationLow Risk R11Single breaker failure causing loss of two linesLow Risk Step 1Step 2Step 3Step 4Step 5Step 6Step 7

10. 10 The exposure to the system is estimated to be, at worst case, 675 hours per year or 7.71% per year, based on planning scenarios. However, the likelihood of this exposure due to operational conditions will be significantly less Step 5: Exposure Analysis Step 1Step 2Step 3Step 4Step 5Step 6Step 7

11. 11 The results of the analysis indicated that to meet Category C criteria, a load drop scheme to reduce SDG&E import to approximately 3100 MW would be required for the N-2 loss of both 500 kV lines. Thus, from an SDG&E import level of 4100 MW, approximately 1000 MW would need to shed. The limiting factors are the thermal ratings of lines in CFE and SCE. Possible voltage collapse was seen when imports were above 3700 MW. Step 6: Consequence of an Outage Step 1Step 2Step 3Step 4Step 5Step 6Step 7

12. 12 Step 7: Report Step 1Step 2Step 3Step 4Step 5Step 6Step 7

13. 13 Performance Evaluation Conclusions The Proposed Path was recommended for Category D with cascading because: Probability of occurrence is extremely low as indicated by MTBF and Robust Line Design analysis. Cascading may occur under planning scenarios, but is not expected during normal operating conditions. SDG&E importing approximately 4100 MW in 2010, 5000 MW load, and only 900 MW of internal generation. SDG&E internal generation capability is expected to be almost 3000 MW in 2010. With an additional 400 MW of generation online the possibility of cascading was significantly reduced The proposed path is in the same right of way for 4 miles(12 towers). The lines terminate at separate substations on the west end. The lines will have diverse and redundant relaying schemes.

14. 14 Project Timeline RPEWG Approval December 19, 2007 Reliability Subcommittee Approval January 10, 2008 Planning Coordination Committee March 6, 2008 WECC Board of Directors April 2008

15. 15 Questions Deepika Sagi – dsagi@semprautilities.comdsagi@semprautilities.com