20180208PAC to Staff Goshen RAS - Assessment.docx

PacifiCorp Main Grid Planning
PRC-(012 through 014)-WECC-CRT2
Attachment B RAS Assessment
RAS Name
Goshen RAS (Goshen Area Load Tripping)
Reporting Party
PacifiCorp
Group Conducting Assessment
PacifiCorp Main Grid Planning
Assessment Date
07/20/2016
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 Goshen RAS is designed to eliminate thermal overloads and low voltage issues in the Goshen 161 kV transmission system for NERC TPL 001-4 P6 contingencies (N-1-1). The combination of outages for which the Goshen RAS could activate are
First Contingency
Second Contingency
Goshen – Threemile Knoll 345 kV Line
Goshen – Kinport 345 kV line
Goshen – Kinport 345 kV line
Goshen – Threemile Knoll 345 kV line
Jim Bridger – Threemile Knoll 345 kV line
Goshen – Kinport 345 kV line
Goshen – Kinport 345 kV line
Jim Bridger – Threemile Knoll 345 kV line
Goshen 345/161 kV auto transformer # 1
Goshen 345/161 kV auto transformer # 2
Goshen 345/161 kV auto transformer # 2
Goshen 345/161 kV auto transformer # 1
Prevent pre-contingency load shedding under N-1-1 outage of the 345 kV source into Goshen and alleviate thermal overloads on the underlying 161 kV transmission lines that feed Goshen for the loss of the 345 kV lines.
The RAS could be activated under heavy load conditions, specifically when the internal generation in the Goshen area is at a lower level.
The RAS will monitor flows on four different transmission elements and upon reaching its emergency rating or flow levels, it will send alarm (or transfer trip) signal to a master controller located at Goshen 161 kV yard. Upon receipt of this signal, the master controller will confirm the loss of the 345 kV source by measuring the flows on the two 345/161 kV auto transformers. If the summation of the flows across the two transformers is less than 45 MW towards Goshen 161 kV then the master controller will issues trip signals to breakers at Goshen, Sugarmill, Rigby, Cinder Butte. The tripping of these breakers will shed load in the Goshen/ Sugarmill/ Rigby area.
The scheme will operate by tripping breakers at Goshen, Rigby Sugarmill and Cinder Butte shedding load if
(1) Flows Don- Pingree 138 kV line are over its emergency rating towards Goshen OR
(2) Flows on Goshen - Blackfoot line are over 35 MW towards Goshen OR
(3) Flows on Goshen - Antelope area over its emergency rating towards Goshen OR
(4) Flows on Goshen-Fishcreek- Grace are over its emergency rating towards Goshen
AND
(1) FLows across the two 345/161 kV transformers at Goshen is less than 45 MW towards Goshen 161 confirming the loss of the 345 kV source.
The Goshen RASis listed as a WideArea Protection Scheme. This designation is appropriate due to the level of load loss exposure (>300 MW).
The operation of RAS could result in loss of load which can be in the order to 450 MW. Some of the generators inside Idaho Falls area may be lost as well. The mis-operation of the RAS can result in significant overloads on the underlying transmission lines serving the Goshen area. Could also result in low voltages in the Goshen area load buses. The mis-operation of the RAS could impact the Dillon – Big Grassy 161 kV line which is part of Path 18 which is an intertie Path.
Study results indicate that the Goshen RAS is still necessary to mitigate thermal overload conditions on 161 kV system in Goshen area.
This RAS assessment included the following:
Study Years
2013-2016
System Conditions
Heavy load conditions in the Goshen area with lower generation inside Goshen load bubble.
Contingencies analyzed
(select what applies)
N-1
N-1-1
N-2
Extreme
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