20180208PAC to Staff Yale Runback Scheme - Assessment.docx

PacifiCorp Main Grid Planning
PRC-(012 through 014)-WECC-CRT2
Attachment B RAS Assessment
RAS Name
Yale Runback Scheme
Reporting Party
PacifiCorp
Group Conducting Assessment
PacifiCorp Area Planning
Assessment Date
12/5/2017
Review the scheme purpose and impact to ensure proper classification, is it (still) necessary, does it serve the intended purposes, and does it continue to meet current performance requirements.
The Yale Runback Scheme is upgraded to mitigate overload conditions on the remaining 115 kV transmission line between Longview and Merwin, between Battleground and Merwin, or between Lewis River and Merwin following the N-1-1 loss of any two of the three lines.
The Yale Runback scheme is listed as a LAPS. This designation is appropriate due to the level of generation tripping (<1000 MW) and load loss exposure (<300 MW). Impacts are limited to thermal overloads on the local 115 kV transmission system for failure of the scheme to operate. The scheme is compliant with TPL-001-WECC-RBP-2.1 requirements.
There are no system impacts beyond partial and temporary loss of local generation for inadvertent operation of the scheme.
Study results indicate that the Yale Runback LAPS is still necessary to mitigate thermal overloads on the Merwin to Cherry Grove, Merwin to Cardwell, and Merwin to Lewis River (Cowlitz PUD)115 kV transmission lines following the loss of any two 115 kV transmission lines.
The scheme is effective for all seasonal load and generation conditions and is always armed.
Study Years
2016 and beyond
System Conditions
The assessment was done with existing conditions, with a maximum combined 310 MW of generation on line at the Merwin and Yale hydroelectric plants. This represents the most stressed condition. The problem is related to generation output, and not to load or grid flow conditions.
Contingencies analyzed
(select what applies)
N-1
N-1-1
N-2
Extreme
N-1-1
Date when the technical studies were completed
December 22, 2015
Does the RAS comply with NERC standards and WECC Criteria?
Yes
Discuss any coordination problems found between this RAS and other protection and control systems during this (most recent) assessment.
None
Provide a Corrective Action Plan if this RAS was found to be non-compliant or had coordination problems during this (most recent) assessment (should be NA for owner’s initial assessment).
N/A
Additional Notes
The assessment is valid until a system topology or generator change takes place because the situation is independent of load or grid flow conditions.