20180208PAC to Staff Grace RAS - Assessment.docx

PacifiCorp Main Grid Planning
PRC-(012 through 014)-WECC-CRT2
Attachment B RAS Assessment
RAS Name
Grace RAS
Reporting Party
PacifiCorp
Group Conducting Assessment
PacifiCorp Main Grid Planning
Assessment Date
03/20/2016
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 Grace RAS is designed to eliminate thermal overloads on Grace – Soda – Threemile Knoll 138kV line for NERC TPL 001-4 P1 & P6 contingencies. The contingencies for which the Grace-Soda-Threemile Knoll 138 kV line overload are
Outage of parallel Grace – Threemile Knoll # 2 138 kV line
Outage of parallel Grace – Threemile Knoll # 2 138 kV line + Threemile Knoll 345/138 kV auto transformer.
Outage of parallel Grace – Threemile Knoll # 2 138 kV line + Outage of Threemile Knoll – Monsanto # 2 138 kV line (bigger conductor)
The presence of the Grace RAS also prevents unnecessary reduction on the Bridger West and Path C southbound transfer capability.
Upon detection of overload at Grace on Grace – Soda 138 kV line, the scheme trips breaker CB 106 at Grace and sends a transfer trip to breaker CB 122 at Soda.
The Grace RASis listed as a Local Area Protection Scheme. This designation is appropriate due to the level of generation tripping (<1000 MW) andload loss exposure (<300 MW). Impacts are limited to thermal overload condition on 138 kV system near Gracefor failure of the scheme to operate.
The failure or mis-operation of the LAPS may result in tripping of the entire Grace – Soda – Threemile Knoll 138 kV line along with the tripping of the parallel Grace – Threemile Knoll #2 138 kV line. Depending on the outage condition, 213 MW of load loss could also occur. Beyond the outage of the two parallel 138 kV lines no additional reliability issues are observed due to the failure of this LAPS. The failure of the LAPS does not result in cascading or uncontrolled separation.
The action of the LAPS may result in loss of 8 MW of hydro generation and load loss of up to 213 MW for an N-1-1 outage.
Study results indicate that the Grace RAS is still necessary to mitigate thermal overload conditions on 138 kV system near Grace. The scheme is effective, with no system performance violation following the actions of the LAPS.
This RAS assessment included the following:
Study Years
2016
System Conditions
2016 heavy load and heavy flows on Path C (N-S) & Bridger West (E-W)
Contingencies analyzed
(select what applies)
N-1
N-1-1
N-2
Extreme
N-1, N-1-1
Date when the technical studies were completed
2016
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
N/A