1. PATH 29 and PATH 32 RATING STUDY
TSS, May 11, 2017
NV Energy (NVE), PacifiCorp (PAC)
Los Angeles Department of Water & Power (LADWP)
NOVEMBER 5, 2015

2. NV Energy Paths
Path 29/32

3. Single Line Diagram

4. Path 29: Path Rating Catalog

5. Path 29
History of Path Establishment The path consists of a 144-mile 230 kV line from Intermountain (IMT) Power Facility (IPF) at Delta, Utah to NVE’s Gonder in Eastern Central Nevada. The path flow is measured at the line’s Gonder end. A 300 MVA regulating XF connects IPF’s 230-kV & 345-kV yards. The IPF 345/230-kV substation is located in the LADWP BA, while the Gonder 230/345 kV sub is located in the NVE/SPPC BA. Transfer Capability (TC): The 200-MW E2W non-simultaneous rating was established in 1987 when the IPF entered service. This rating is based on the “rule-of-thumb” criterion of 30 degree power angle difference between the sending and the receiving line end, and on power flow studies (P0 conditions). Interaction with Other Transfer Paths: At the maximum flow conditions, the TC of the line is sensitive to the flows on the Pavant-Gonder 230-kV line. Simultaneous flow capability of these two lines at the path 32 cut-plane was studied in the 2016 NVE NERC study, which concluded that ratings of path 29 and of the IMT XF are two limiting factors for path 32. Seasonal System Operating Limit studies by the Rocky Mountain Region Study Group establish a nomogram relationship between Path 35 and 78 (Pinto-Four Corners) vs. IPP Net Import. The IPP Net Import is the combined imports on both Path 28 and Path 29 which is scheduled over Path 27. For disturbances where both of the IPF-Mona 345-kV lines are tripped, a transfer trip protection trips the IPF-Gonder 230-kV line.

6. Path 29: Need for Re-Study
Path 29 was established before 1/1/1994 & has an “Existing” WECC rating. Since then many changes had occurred: a) path 32 (of which path 29 is a part) was established, b) new facilities near the IMT bus, including the wind farms at the IMT 345 kV bus were added, c) IMT 345/230kC XF obtained an “emergency” rating of 351 MVA. The 30 degree “rule-of-thumb” limitation is no longer valid, since there’re much better modeling tools (comparing with 1987) are available, which use reliable stability time-domain simulations (instead of simplified rules). The line closing angle protection limitations today are determined through a specific study allowing setting it to a much higher degree than 30°. Currently, the closing angles for “Sync-Check” relays at the Gonder end of all 230 kV lines are set to 40° (proving the 30° “rule-of-thumb” obsolete). Also: neither path 29 nor path 32 have ever been limited by stability issues but by the system thermal limits. The flow on path 29 in E2W direction reached 230 MW in the latest 2016 NVE NERC study. This exceeds the 200- MW path rating and is within the system reliability requirements (due to the new IMT XF emergency rating).

7. Path 32: Path Rating Catalog

8. Path 32
History of Path Establishment The path consists of a 149-mile 230 kV line from NVE’s Gonder located in Eastern Nevada to PacifiCorp’s Pavant located in Central Western Utah and Gonder – IMT line or path 29. The path flow is calculated as a sum of flows on Gonder – Pavant at Utah/NV border & Gonder – IMT at the Gonder end (same as path’s 29). 2×300 MVA XFs connect Gonder 230-kV & 345-kV yards, and further a 24-mi 345 kV line leads to NVE’s RBS 345/500 kV substation. On the 230 kV side, Gonder is connected through a 116–mile 230 kV line to Frontier and further to Ft. Churchill plant. All of these facilities are located in the NVE BA, while the Pavant 230 kV substation is located in the PAC’s BA. Path 32 establishes a cut-plain between NVE, LADWP & PAC BAs. Transfer Capability: The 440-MW E2W and 235 MW W2E non-simultaneous ratings were established in 1999 when the Gonder – Pavant line was first put into service. The ratings were originally limited by:

9. Path 32: Transfer Capability
E2W: Gonder transient and post-transient voltage deviation for loss of Midpoint – Humboldt 345 kV line (mitigated by Gonder “Voltage mitigation RAS”). Pavant 230 kV bus voltage for loss of the IPP - Gonder 230 kV line. W2E: Falcon 345/230 XFMR overload for loss of the Valmy - Coyote Crk 345 kV line (mitigated by Falcon XF overload RAS) or Ft. Churchill 230/120 kV XFMR overload for loss of the Falcon-Gonder 345 kV line or Limits & Interactions: E2W direction was limited by the interaction with path 16 and by the SPPC overall import limit. After RBS – HA 500 kV line entered service in 2013, this interaction was significantly reduced, effectively eliminating this flow limitation for path 32. The Pavant bus voltage limitation (post-transient voltage deviation) also was alleviated due to the overall changes in the PAC/NVE system (including adding of Black Rock, Osceola, and ONL projects). Interaction between path 29 and 32 (which includes path 29): The extent of the interaction is actually determined by the flow split between IMT-Gonder & Pavant – Gonder lines. The studies performed to-date demonstrate that this split is almost even with IMT – Gonder flow being typically higher (e.g., in NVE’s 2016 NERC study IMT-Gonder was at 52 % & Pavant – Gonder at 48 % of the total path 32 flow). This study will also explore a potential for a nomogram between path 29 & 32.

10. Path 32: Limits & Interactions
Limits & Interactions: E2W direction was limited by the interaction with path 16 and by the SPPC overall import limit. After RBS – HA 500 kV line entered service in 2013, this interaction was significantly reduced, effectively eliminating this flow limitation for path 32. The Pavant bus voltage limitation (post-transient voltage deviation) was alleviated due to the overall changes in the PAC/NVE system (including adding Black Rock, Osceola, and ONL projects). Interaction between path 29 & 32: Is determined by the flow split between IMT-Gonder & Pavant – Gonder lines. The studies performed to-date demonstrate that this split is almost even with IMT – Gonder flow being typically higher (e.g., in NVE’s 2016 NERC study IMT-Gonder was at 52 % & Pavant – Gonder at 48 % of the path 32 flow). The new study will explore a potential for a nomogram between path 29 & 32.

11. Need for Re-Study Due to many changes on both Gonder – IMT & Gonder – Pavant lines that happened since the path establishment (as described in section 2) and the need to change the definition of the path the need for the re-study has arisen. The definition of the path, to match the current configuration will be the sum of flows on the following lines: Osceola (NVE) – Black Rock (PAC) 230 kV line measured at Utah/NV border. Gonder (NVE) - Intermountain (LADWP/IPP) 230 kV line measured at Gonder. During planning and operating studies recently performed by NVE it was observed that addition of the One Nevada Line project (including folding of the Gonder – Falcon 345 kV line into Robinson Summit (RBS) and a 525 kV line from RBS to H. Allen) strengthened the SPPC system and improved flowability (and thus achieving the target flow) on path 32.

12. Spring Valley Wind – 150 MW

13. Request for Expedited Rating Process

14. STUDY PLAN

15. Study Objectives and Purpose
The objective of this study is to demonstrate that: a) The existing path 32 non-simultaneous ratings of 440 MW (E2W) & 235 MW (W2E) do not violate WECC/NERC Planning Standards or local reliability criteria, b) Determine a new path 29 non-simultaneous E2W rating, with target of 250 MW, that adheres to WECC/NERC Planning Standards & local criteria, c) Identify any WECC paths with simultaneous interactions and establish appropriate simultaneous ratings if needed. This work includes exploring possible benefits of creating a nomogram between paths 29 and 32.

16. Questions ? Contacts: NVE:
Alex Fratkin at ( )
Adeline Grubb at ( )
PacifiCorp:
Craig Quist at ( )
Tejas Tamhankar at ( )
LADWP:
Faranak Sarbaz, ( )