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Sunrise Powerlink and Southwest Powerlink Reliability Performance Evaluation

Double Line Outage Probability Analysis

March 6, 2008

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RPEWG and RS Recommendation

After reviewing SDG&E’s 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.

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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 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7

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Proposed and Alternative Paths

Proposed Path – approximately 4 miles Alternative Path – approximately 36 miles

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12 Tower Structures

Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7

Tower 50281 Tower 50280 Tower 50279

Tower 50273Tower 50276 Tower 50274Tower 50275

Tower 50277Tower 50278

Tower 50272 Tower 50271 Tower 50270

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Step 2: Outage Database – The Sample

SWPL is SDG&E’s 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 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7

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Step 3: Zero Events - Corrected MTBF

MTBF is 928 years

PT, PL, and PH 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.

Event Cause P1 (events/year) MTBF1 (years)

PT Historical Terminal 0 0

PL Historical Line 0 0

PIND Independent 0.0010 968.7053

PH Human 0 0

PB BF & M 0.0000458 21854.375

PTOTAL Total 0.0011 927.5895

Summary of Results (Corrected)

Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7

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One Event - Corrected MTBF

MTBF is 21 years PT , PL, and PH 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.

Event Cause P2(events/year) MTBF2(years)

PT Historical Terminal 0.025 >40

PL Historical Line 0.0204 >49

PIND Independent 0.0010 968.7053

PH Human < .0013 >775

PB BF & M 0.0000458 21854.375

PTOTAL Total 0.0478 20.9301

Summary of Results (Corrected)

Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7

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Step 4: Risk Factor SummaryRisk Risk Factor

R1 Fire affecting both lines Low Risk

R2 One tower falling into another line Low Risk

R3 Conductor from one line being dragged into another line Low Risk

R4 Lightening strikes tripping both lines Low Risk

R5 Aircraft flying into both lines Low Risk

R6 Station related problems resulting in loss of two lines for a single event

Low Risk

R7 Natural disasters Low Risk

R8 Loss of two lines due to an overhead crossing Low Risk

R9 Loss of two lines due to vandalism/malicious acts Low Risk

R10 Flashover to vegetation Low Risk

R11 Single breaker failure causing loss of two lines Low Risk

Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7

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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

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SDG&E Load Duration Curve

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2006 Actual Load 2006 Forecast Load2010 Forecast Load Load

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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 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7

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Step 7: Report

Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7

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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.

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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

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Questions

Deepika Sagi – dsagi@semprautilities.com