Puget Sound Area Transmission Expansion Plan Sensitivity Results Review

Overview Covington Transformer Sensitivity ◦ No 500 kV Bus NODO ◦ Option 8 One Transformers ◦ Option 8 Two Transformers All Lines In Service & 2850 MW Transfer ◦ Major Projects Without Bothell – SnoKing – Maple Valley Bothell – SnoKing – Maple Valley Rebuild Sensitivities ◦ Lakeside Transformer Project  Rebuild the two 115kV lines between Sammamish-Lakeside-Talbot to double circuit 230 kV, add a single 230/115 kV transformer at Lakeside, Tap Bothell – Sammamish Line into SnoKing and rebuild Bothell-SnoKing 230 kV Lines ◦ Bothell – SnoKing – Maple Valley High Temp Wire No RAS ◦ Bothell – SnoKing – Maple Valley High Temp Wire With RAS ◦ 2 nd Monroe – Echo Lake Line & Bothell – SnoKing Rebuild ◦ 2 nd Monroe – Echo Lake Line & Bothell – SnoKing High Temp Wire ◦ No SnoKing – Maple Valley Rebuild ◦ SnoKing – Maple Valley High Temp Wire TCRM Limitations for Major Projects Case Future ATC Runs

Major Projects Note: The Sedro Transformer Project was on the Major Project list in the last version of the report. It has been added to the base case as an assumed project.

Covington Transformer Sensitivity Covington Transformer Project Without 500 kV Covington Bus ◦ Covington Transformer #5 Accounts for a Large Amount of Remaining WSN TCRM

NODO Transformer Sensitivities Option 8 With Cable Reactors Option 8 With Cable Reactors and 2 nd NODO Transformer

NODO Transformer Sensitivities Option 8 With Cable Reactors ◦ Increased SN TCRM Values Attributed to NODO 230/115 kV Transformer Option 8 With Cable Reactors and 2 nd NODO Transformer ◦ Increased SN TCRM Values Attributed to Canal – NODO 115 kV Line Add Reactors to Canal – NODO & Broad Street - NODO115 kV Lines

2850 MW Transfer Sensitivities Intertie NS Rated Capability (2850 MW) ◦ All Lines In Service ◦ Major Projects Without Bothell – SnoKing – Maple Valley Rebuild

2850 MW Transfer Observations Base Case Limitations ◦ SNS  Seattle 115 kV Cables  Portal Way Transformer ◦ SSN  Seattle 115 kV Cables  Custer – Monroe 500 kV Line ◦ WNS  Portalway Transformer ◦ WSN  Covington 500/230 kV Transformer Base Case With SCL Reactors Shows Little Benefit due to Limitations Seen on Bothell – SnoKing 230 kV Lines Major Projects Case Without the Bothell – SnoKing – Maple Valley Rebuild Shows Limitations on Bothell – SnoKing – Maple Valley Lines All Significant Limitations are Addressed by Major Projects Except Custer Monroe 500 kV Line

Bothell – SnoKing - Maple Valley Rebuild Sensitivities Lakeside Transformer Project ◦ Rebuild the two 115kV lines between Sammamish-Lakeside-Talbot to double circuit 230 kV, add a single 230/115 kV transformer at Lakeside, Tap Bothell – Sammamish Line into SnoKing and rebuild Bothell-SnoKing 230 kV Lines

Observations For Bothell – SnoKing – Maple Valley 230 kV Line Rebuild Alternatives Lakeside Transformer Project ◦ Valid Alternative ◦ Spread out TCRM Reduction Among Remaining Limiting Elements

Bothell – SnoKing - Maple Valley Rebuild Sensitivities Bothell – SnoKing – Maple Valley High Temperature Wire With Bothell – SnoKing RAS Without Bothell – SnoKing RAS deg Operation 1739 Amps, 693 MVA

Observations For Bothell – SnoKing – Maple Valley 230 kV Line Rebuild Alternatives Bothell – SnoKing – Maple Valley High Temperature Wire ◦ TCRM Increase Attributed to Limitations on Bothell – SnoKing – Maple Valley Lines  Typical Outage Combination No RAS  Primary: Multiple  Secondary: L_BOTHELL230-SNOKS1230C1-MS  Typical Outage Combination With RAS  Primary: RAVER SCHULTZ 500  Secondary: N-2: CHIEF JO-MONROE 500 & CHIEF JO- SNOHOMISH 345 #3

Bothell – SnoKing - Maple Valley Rebuild Sensitivities 2 nd Monroe – Echo Lake 500 kV Line ◦ With Bothell – SnoKing Rebuild ◦ With Bothell – SnoKing High Temp Wire

Observations For Bothell – SnoKing – Maple Valley 230 kV Line Rebuild Alternatives 2 nd Monroe – Echo Lake 500 kV Line  With Bothell – SnoKing Rebuild  With Bothell – SnoKing High Temp Wire ◦ Valid Alternatives ◦ Spread out TCRM Reduction Among Remaining Limiting Elements ◦ Limitations to Bothell – SnoKing Lines Remain for High Temp Wire Option

Bothell – SnoKing - Maple Valley Rebuild Sensitivities SnoKing – Maple Valley Alternatives ◦ No SnoKing – Maple Valley Rebuild ◦ SnoKing – Maple Valley High Temp Wire

Observations For Bothell – SnoKing – Maple Valley 230 kV Line Rebuild Alternatives No SnoKing – Maple Valley Rebuild ◦ SnoKing – Maple Valley Limitations Attribute Majority of TCRM increase SnoKing – Maple Valley High Temp Wire ◦ Valid Alternative ◦ Low TCRM Levels Remain for SnoKing – Maple Valley Lines

TCRM Limitations for Major Projects Case Elements With TCRM Levels Over 1000 for Major Projects Case ◦ WSN  Snohomish 230/345 kV Transformer #1  TCRM = 8703  PTDF ≈ 3.5, OTDF ≈ 6.6  Mercer Island Tap – Shuffleton 115 kV Line  TCRM = 6550  PTDF ≈ 0.95, OTDF ≈ 3.6  Everett – Navy 115 kV Line  TCRM = 5771  PTDF ≈ 0.85, OTDF ≈ 2.35  Murray – Snohomish 230 kV Line  TCRM = 3087  PTDF ≈ 4.4, OTDF ≈ 16.7  Delridge – Duwamish 230 kV Line  TCRM = 2588  PTDF ≈ 1.1, OTDF ≈ 2.0 ◦ Comments

Planned ATC Runs North Downtown Substation with Reactors on Canal – NODO & Broad Street – NODO Lines Rerun All Runs With Rating Corrections to kV Transformers in Puget Area From BPA – ColumbiaGrid Meeting ◦ Upgrade SCL Cables ◦ Third SCL Cable ◦ 500 kV Loop Option With 230 kV Maple Valley – SnoKing Line Suggestions?

Questions?