20180307PAC to Staff WY Aeolus West Transmission Assessment.pdf

*PRELIMINARY DRAFT*
Aeolus West Transmission Path
Transfer Capability Assessment
Updated Study Report
Revision 2.0
February 2018
Prepared by
PacifiCorp -Transmission Planning
Updated
Aeolus West Transmission Path
Transfer Capability Assessment
Table of Contents
Executive Summary .............................................................................................1
1 Introduction ................................................4
1.1 Purpose ............................................................................................4
1.2 Plan of Service ......................................................................4
1.3 Planned Operating Date ........................................................5
1.4 Scope ...........................................................................5
2 Study Criteria..............................................................................6
2.1 Thermal Loading .........................................................................................6
2.2 Steady State Voltage Range .............................................................................6
2.3 Post-Transient Voltage Deviation...............................................................7
2.4 Transient Stability Analysis Criteria..................................................................7
2.5 Transient Voltage Response..............................................................................7
3 Base Case Development...............................................................................9
3.1 Base Case Selection ................................................................................9
3.2 Generating Facility Additions .....................................................................10
3.3 Base Case Modification and Tuning.....................................................................11
4 Path Studies ....................................................................................................12
4.1 Aeolus West vs.TOT 4B ................................................................................12
4.2 Base Case Development.......................................................................14
4.3 Transient Stability Analysis .............................................................................15
5 Sensitivity Analysis...............................................................................15
6 Study Conclusions ..................................................................................15
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Aeolus West Transmission Path
Transfer Capability Assessment
Executive Summary
This assessment was conducted to document the Transfer Capability of the Aeolus Westi
transmission path once the Gateway West -Subsegment D.22 (Bridger/Anticline-Aeolus)
transmission facilities (D.2 Project)are added to the Wyoming transmission system and
assumed resources identified in the PacifiCorp 2017R RFP3 Shortlist were added.
The Aeolus West transmission path (see Figure 1)is a new path that will be formed by adding
the D.2 Project in parallel with the TOT 4A4 (Path 37)transmission path facilities.The
anticipated in-service date for the D.2 Project is November 2020.The D.2 Project is part of
PacifiCorp's Energy Vision 2020 which includes the followingmajor transmission facilities:
Aeolus 500/230 kV substation,Figure 1:Aeolus West Transmission Path
Shirley Basin -Freezeout 230 kV line
loop-in to Aeolus,
Aeolus Wesi
Anticline 500/345 kV substation,
Aeolus -Anticline 500 kV new line,
Bridger -Anticline 345 kV new line,
Shirley Basin -Aeolus 230 kV #1 line
rebuild,
Shirley Basin -Aeolus 230 kV #2 line -1
(16-mile),
1 The Aeolus West transmission path will include the followingmajor transmission elements:Aeolus*-Anticline
500 kV,Platte*-Latham 230 kV,Mustang*-Bridger230 kV and Riverton*-Wyopo 230 kV transmission
lines.(*meter location)
2 Gateway West -Subsegment D.2 is a key component of the Energy Vision 2020 (EV2020)initiative that was
announced by PacifiCorp on April 4,2017.Other components of the EV2020 initiative include repowering
PacifiCorp's existing wind fleet in southeast Wyoming and adding approximately 1,100 MW of new wind
generation east of Bridger/Anticline.[Subsequent to the initial announcement,technical studies have
demonstrated that as high as 1,510 MW can be integrated east of Bridger/Anticline.]
3 The PacifiCorp 2017R Request for Proposals for renewable resources (2017R RFP)solicited cost-competitive
bids for up to 1,270 MW of new or repowered wind energy interconnecting with or deliveringto PacifiCorp's
Wyoming system with the use of third-party firm transmission service and any additional wind energy located
outside of Wyoming capable of deliveringenergy to PacifiCorp'stransmission system that will reduce system
costs and providenet benefits for customers.
4 The existing TOT 4A (Path 37)transmission path is comprised of the Riverton*-Wyopo 230 kV,Platte -
Standpipe*230 kV and Spence*-Mustang 230 kV transmission lines.(*meter location)
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Aeolus -Freezeout 230 kV line rebuild,
Freezeout -Standpipe 230 kV line reconstruction,
Latham dynamic voltage control device,
Construct a 230 kV single circuit transmission line to replace 7-miles of the Ben
Lomond -Naughton 230 kV #1 circuit,which resides double-circuit lattice towers with
the Ben Lomond -Birch Creek 230 kV #2 line,and
Reconductor the 795 ACSR portion of the Railroad -Croydon 138 kV line with 1222
ACCC high temperature conductor.
The WECC 2021-22 HW power flow base case was utilized for the Aeolus West transfer
capability assessment studies.In support of the EV2020 initiative,which calls for the addition
of new and repoweredwind resources in Wyoming,the base case was modified to achieve the
transfer levels evaluatedby utilizingPacifiCorp 2017R RFP Shortlist resources,which added
1510 MW east of the Aeolus West "cut plane"and 221 MW in southwest Wyoming.For
different Aeolus West transfer levels (heavy and light)and 2400 MW flow across Jim Bridger
West,resource levels in eastern Wyomingwere varied relative to the Jim Bridger Generation
Plant in Central Wyoming and the Emery/Hunterand Huntingtongeneration in Central Utah.
Contingenciesthat were considered in this analysis include:
N-1 of D.2 Project facilities
N-1,N-2 Bridger contingencies
All Eastern,Central and North Wyoming transmission system contingencies performed
as part of the TPL-001-4 annual assessment.
For the preliminary Transfer Capability assessment,simultaneous interaction between the
Aeolus West path and the TOT 4B path was evaluated;however,the interactions with other
transmission paths (YellowtailSouth,Jim Bridger West,TOT lA and TOT 3)were monitored
throughout the study.
Conclusions
Technical studies demonstrated that with the addition of the planned D.2 Project facilities to
the Wyoming transmission system,system performance will meet all NERC and WECC
performance criteria.
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Transfer Capability Assessment
Preliminary power flow studies demonstrate that by utilizingexisting and planned southeast
Wyomingresourcess,the Aeolus West transmission path can transfer up to 1792 MW under
simultaneous transfer conditions with the TOT 4B transmission path,effectively6 ÏRCTenSing
the east to west transfer levels across Wyoming by 914.5 MW.Power flow findings also
indicated:
Dynamic voltage control is necessary at the Latham 230 kV substation to mitigate low
voltage conditions resulting from loss of Bridger/Anticline -Aeolus transmission
facilities.
Under certain operating conditions,one Remedial Action Schemes (RAS)will need to
be implemented to trip generation followingoutage of specific transmission facilities.
The location (and output level)of new and repoweredwind resources can influence the
transfer capability level across the Aeolus West transmission path,the Aeolus West
and TOT 4B nomogram curve and the area under the nomogram curve.
Dynamic stability studies evaluating a wide range of system disturbances are under way and
will be presented in a follow-on technical report.
*Eastern Wyoming Resources:Existing Wind:1124 MW,Dave Johnston (net)717 MW,New Wind -East of
the Aeolus West "cut plane":1510 MW at various locations.
6 Effectivetransfers were determined by subtracting the existing TOT 4A path maximuml3 transfer level (960
MW)from the Aeolus West transfer level (1792 MW)and adding the Platte area loads (82.5 MW)that are up-
stream of the Aeolus West metering point.
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1 Introduction
1.1 Purpose
The purpose of the study is to demonstrate that the interconnectedtransmission Bulk Electric
System (BES)in Wyomingwith the D.2 Project added can support the PacifiCorp 2017R RFP
Shortlist resources and can be operated reliably during normal and contingency operations
throughoutthe planning horizon.To achieve this purpose,the study will:(1)identify the new
Aeolus West transmission path limitations,(2)evaluate the interactions between the Aeolus
West and the TOT 4B transmission paths and develop a nomogram that depicts system
limitations and (3)identify the need for various Remedial Action Schemes (RAS).
This report summarizes the results of the power flow portion of Aeolus West transfer capability
assessment and demonstrates that performance of the BES in Wyomingwith the addition of
the D.2 Project will meet all NERC and WECC performance criteria.
1.2 Plan of Service
The D.2 Project consists of the followingsystem improvements:
1.A new 500/230 kV Aeolus substation
2.A new 230/500 kV,1600 MVA transformer at Aeolus
3.Loop-in the Shirley Basin -Freezeout 230 kV line into Aeolus,
4.A new 500/345 kV Anticline substation
5.A new 500/345 kV,1600 MVA transformer at Anticline
6.A new 137.8-mile 3x1272 ACSR (Bittern),500 kV line between Aeolus and Anticline
substations
7.A new 5.1-mile 3x1272 ACSR (Bittern),345 kV line between Anticline and Jim
Bridger substations
8.A new 50 MVAr reactor at Aeolus 230 kV bus
9.A new 200 MVAr shunt capacitor bank at Aeolus 500 kV bus
10.A new 200 MVAr shunt capacitor bank at Anticline 500 kV bus
11.Rebuild of the Aeolus -Shirley Basin 230 kV #1 line to 2xl557 ACSR/TW
(Potomac/TW)conductor
12.A new 2xl557 ACSR/TW (Potomac/TW)Aeolus -Shirley Basin 230 kV #2 line
13.Rebuild of the Aeolus -Freezeout 230 kV lines to 2x1272 ACSR (Bittern)conductor
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14.Reconstruction of Freezeout -Standpipe 230 kV lines to 2x1272 ACSR (Bittern)
conductor
15.A new dynamic reactive device at Latham 230 kV substation.
16.Construct a 230 kV (2-795 ACSR)transmission line to replace 7-miles of the Ben
Lomond -Naughton 230 kV #1 circuit,which resides double-circuit lattice towers with
the Ben Lomond -Birch Creek 230 kV #2 line,and
17.Reconductor 2.35 miles of 795 ACSR 138 kV line between Railroad and Croydon with
1222 ACCC high temperature conductor.
1.3 Planned OperatingDate
The plan of service for the facilities to be operational is by November 2020.
1.4 Scope
The Aeolus West Transfer Capability assessment assumes the addition of new wind generation
facilities as noted in Table 1,which are associated with the PacifiCorp interconnection queue
and its 2017R RFP Shortlist resources.While the new technology and model information of
the repowered units was used in the steady-state and transient stability analysis (currently
underway),no incremental MW output was considered;i.e.,each repowered facility was
limited to its current Large GeneratorInterconnection Agreement (LGIA)capacity.The study
Table 1:Generating Resources
Wyoming Thermal East Wyoming -Existing New Wyoming Wind
Generation Wind
2396 MW 1124 MW 1731 MW
Dave Johnston:717 MW (Foote Creek,Rock River,Eastern Wyoming (Aeolus,
Wyodak (PacifiCorp):268 High Plains,SevenMile Shirley Basin,Windstar):1270
MW Hill,Dunlap,Root Creek,MW
Jim Bridger (PacifiCorp):Top of the World,Northern Wyoming (Bighorn
1411 MW Glenrock,Three Buttes,Basin):240 MW
Chevron)SouthwestWyoming (Uinta
County):221 MW
See Table 4.
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was performed using a 2021-22 heavy winter WECC approved case which was modified to
include the D.2 Project facilities and applicable PacifiCorp 2017R RFP Shortlist wind
generation transmission facilities.The system model assumed summer line ratings to assess
the thermal limitation of the Wyoming system.Load served from Platte is normally
represented as an open point between Platte -Whiskey Peak 115 kV.The system configuration
with Platte 115 kV normallyopen is presently the most limitingscenario for the existing TOT
4A/4B nomogram.
2 Study Criteria
While this report is intended to summarize the results of updated power flow studies,for
clarity,the study criteria that is used for the evaluation of both power flow and dynamic
stability studies will remain in the document.
2.1 Thermal Loading
For system normal conditions described by the PO'event,thermal loading on BES transmission
lines and transformers is required to be within continuous ratings.
For contingency conditions described by Pl-P7 category planning events,thermal loading on
transmission lines and transformers should remain within 30-minute emergency ratings.
The thermal ratings of PacifiCorp's BES transmission lines and transformers are based on
PacifiCorp's Weak Link Transmission Database and Weak Link Transformer Database as of
March 31,2017.
2.2 Steady State Voltage Range
The steady state voltage ranges at all PacifiCorp BES buses shall be within acceptable limits
as established in PacifiCorp's Engineering Handbook section 1B.3 "Planning Standards for
Transmission Voltage""as shown below.
7 Facility outage events that are identifiedwith "P"designations are referenced to the TPL-001-4 NERC standard.
*PacifiCorp Engineering Handbook "Planning Standards for Transmission Voltage,"April 8,2013.
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Table 2:Voltage Criteria
Contingency Conditions (P1-Operating System Normal Conditions (PO)P7)Configuration Vmin (pu)Vmax (pu)Vmin (pu)Vmax (pu)
Looped 0.95 1.06 0.90 1.10
Radial 0.90 1.06 0.85 1.10
Steady state voltage ranges at all applicable BES buses on adjacent systems were screened
based on the limits established by WECC regional criterion as follows:
95%to 105%of nominal for PO event (system normal),
90%to l10%of nominal for Pl-P7 events (contingency).
2.3 Post-Transient Voltage Deviation
Post-contingency steady state voltage deviation at each applicable BES load serving bus
(having no intermediate connection)shall not exceed 8%for Pl events.
2.4 Transient StabilityAnalysis Criteria
All voltages,frequencies and relative rotor angles are required to be stable and damped.
Cascading or uncontrolled separation shall not occur and transient voltage response shall be
within established limits.
2.5 Transient Voltage Response
Transient stability voltage response criteria are based on WECC Regional Performance Criteria
WRl.3 through WRl.5 as follows:
Transient stability voltage response at the applicable BES buses serving load (having
no intermediate connection)shall recover to at least 80%of pre-contingency voltage
within 20 seconds of the initiating event for all Pl-P7 category events,for each
applicable bus serving load.
For voltage swings followingfault clearing and voltage recovery above 80%,voltage
dips at each applicable BES bus serving load (having no intermediate buses)shall not
dip below 70%of pre-contingency voltage for more than 30 cycles or remain below
In some situations,voltages may go as high as 1.08 pu at non-load buses,contingent upon equipment rating
review.
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80%of pre-contingency voltage for more than two seconds for all Pl-P7 category
events.
For contingencies without a fault (P2-1 category event),voltage dips at each applicable
BES bus serving load (having no intermediate buses)shall not dip below 70%of pre-
contingency voltage for more than 30 cycles or remain below 80%of pre-contingency
voltage for more than two seconds.
The followingcriteria were used to investigate the potential for cascading and uncontrolled
islanding:
Load interruption due to successive line tripping for thermal violations shall be
confined to the immediate impacted areas and shall not propagate to other areas.The
highest available emergency rating is used to determine the tripping threshold for lines
or transformers when evaluating a scenario that may lead to cascading.
Voltage deficiencies caused by either the initiating event or successive line tripping
shall be confined to the immediate impacted areas,and shall not propagate to other
areas.
Positive damping in stability analysis is demonstrated by showing that the amplitude of power
angle or voltage magnitude oscillations after a minimum of 10 seconds is less than the initial
post-contingency amplitude.Oscillations that do not show positive damping within a 30-
second time frame shall be deemed unacceptable.
Stability studies shall be performed for planning events to determine whether the BES meets
the performance requirements.
Single contingencies (Pl category events):No generating unit shall pull out of
synchronism (excludes generators being disconnected from the system by fault clearing
action or by a special protection system).
Multiple contingencies (P2-P7 category events):When a generator pulls out of
synchronism in the simulations,the resulting apparent impedance swings shall not
result in the tripping of any transmission system elements other than the generatingunit
and its directlyconnected facilities.
Power oscillations are evaluated by exhibiting acceptable damping.The absence of
positive damping within a 30-second time frame is considered un-damped.
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Transfer Capability Assessment
3 Base Case Development
3.1 Base Case Selection
The base case developmentprocess involves selecting an approvedWECC base case,updating
the models to represent existing and planned facilities (D.2 Project transmission and wind
generation facilities)and then tuningthe cases to maximum transfer conditions on the WECC
transmission path(s)being studied.For this study purpose,the published WECC base case that
is close to the projects'in-service date of November 2020,which has average load conditions
based on 2021 load projection and availability of a stability case,was selected.The WECC
approvedbase case 2021-22 HW (created on August 19,2016)was selected,which meets these
criteria.This study focused on simultaneous transmission path interaction in the Wyoming area
between the Aeolus West and the TOT 4B transmission paths;however,other transmission
paths such as Yellowtail South (non-WECC path),Jim Bridger West,TOT lA and TOT 3 (See
Appendix A for path definitions)were monitored throughout the study.
The various critical components for this study purpose from selected 2021-22 HW base case
are listed below:
Table 3:Wyoming Load,Generation and Platte Normal Open Configuration in Base Case
North Wyoming PAC Load (including Wyodak load of 42 391 MWMW)
North Wyoming -Western Area Power Administration 211 MW(WAPA)Load
Eastern Wyoming PAC Load (including DJ load of 56 MW)474 MW
Eastern Wyoming PAC loads on WAPA system 95 MW
Central Wyoming Load (including JB load of 130 MW)434 MW
Yellowtail South Flow 192 MW
Yellowtail Generation 140/260MW (Online/Max)
WAPA's Existing Small Generation*°in North Wyoming 26/50 MW(Online/Max)
WAPA's Existing Small Generation"in Eastern Wyoming 484/584 MW(Online/Max)
Wyodak Generation (PacifiCorp/Black Hills)350/380 MW (Online/Max)
io WAPA's small generation in north Wyoming includes;Boysen,BBill,Heart MT,Shoshone,Spring Mtn
"WAPA's small generation in eastern Wyoming includes;Alcova,Fremont,Glendo,Guernsy,Kortes,Seminoe,
CLR_l,SS_Genl AND CPGSTN
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Dry Fork Generation (Basin Electric)420/440 MW (Online/Max)
Gross Laramie River Generation I (WAPA's swing
.605 MW(Max)machine)
Gross Laramie River Generation II 590/605 MW(Online/Max)
Gross Dave Johnston (DJ)Generation 700/774 MW(Online/Max)
Total Existing PAC East Wyoming Windl2 Generation 885.7/1124 MW (Online/Max)
Rapid City DC W Tie 130 W2E (200 MW-bidirectional)
Stegall DC Tie 100 E2W (110 MW-bidirectional)
Sydney DC Tie 196 E2W (200 MW-bidirectional)
TOT 4A 627 MW
TOT 4B 469 MW
Jim Bridger (JB)Generation 2200 MW
Jim Bridger West Flow 2027 MW
TOT 3 1259.1 MW
TOT lA 195 MW
Platte -Mustang 115 kV Normal Open point Platte -Normal Open
3.2 GeneratingFacility Additions
Based on the wind generation resources in PacifiCorp's interconnection queue in combination
with projects identified in the PacifiCorp 2017R RFP Shortlist,an updated transmission
assessment of the Aeolus West transmission path was performed.Projects with an in-service
date beyond 2020 were excluded.In conducting this analysis,the generating resources
identified in Table 4 were added to the base case and technical studies identified in Section 4
were performed.While Table 4 provides the general location of each of the PacifiCorp 2017R
RFP Shortlist resources,Figure 2 provides an overview of the PacifiCorp's Wyoming
transmission system,gives a visual illustration of the location of each of the existing and new
generation (noted in red)resources,and identifies location of the Aeolus West and TOT 4B
transmission path constraints.
12 PAC eastern Wyoming wind generation includes;Root Creek,Three Buttes,Top of World,Glenrock,Rolling
Hills,Dunlap.Seven Mile Hill,Foote Creek and High Plains wind generation
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Table 4:PacifiCorp 2017R RFP Shortlist Generation Resources
Proposed New Wind LGI Queue Project Point of InterconnectionFacilitiesNumberSize
Eastern Wyoming
(Aeolus/Shirley Q706 250 MW Aeolus 230 kV
Basin/Windstar Area)
Eastern Wyoming Q707 250 MW Shirley Basin 230 kV
(Aeolus/Shirley Q708 250 MW Shirley Basin 230 kVBasin/Windstar Area)Q712 520 MW Windstar 230 kVSouthwestWyoming
(Uinta County)Q715 120 MW Canyon Compression-Railroad 138 kV line
SouthwestWyoming Q8 10 10 1 MW Canyon Compression-Railroad 138 kV line(Uinta County)
TOTAL 1491 MW
See Appendix B for detail on new and repowered wind farm modelling assumptions.
*UPDATES IN PROGRESS*
3.3 Base Case Modification and Tuning
The 2021-22HW base case was modified to reflect the most recent Foote Creek,High Plains,
Top of the World and Three Buttes wind generationmodeling as per the recent MOD-032 data
submitted by each generator owner (GO).Transmission line impedances between Dave
Johnston and Standpipe were verified and updated and the transmission line ratings in the
2021-22 heavy winter case were modified to summer ratings,which represent the most
conservative thermal limitations.The Platte -Standpipe 230 kV dynamic line rating of
608/666/680 MVA was assumed during the analysis.
The PacifiCorp 2017R RFP Shortlist resources listed in Table 4 were added to the base case
and the existing repowered wind farm generator models and collector system data were
updated.The Aeolus West path was stressed by maximizingthe output on all of the existing
and new wind generation facilities.Output for the repowered wind generation facilities was
limited to the existing LGI agreement generation levels.The additional generation in southeast
Wyomingwas re-dispatched with Jim Bridger,central and southern Utah generation.The Jim
Bridger generationoutput was maintained such that Jim Bridger West path flows were held at
2400 MW.
As per the available data obtained for the various wind generation facilities at the time of this
study analysis,the base cases were reviewed and adjusted to ensure voltages in the collector
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Transfer Capability Assessment
system of wind generationfacilities were below 1.05 p.u.and that there was no reactive power
loop flow between the main generator step-up transformers GSU's for wind generationfacility.
Figure 2
Existing/Proposed Wyoming Generation Resources,and Transmission Constraints
PacifiCorp ¯¯¯||Aeolus West/TOT 4B s,
Wyoming Transmission
Constraints Gria,d
Diy Fort.
Gregori
Bas "No<th Wyoming y,LceAca:
TOT 4B sa e
Creek Creek
230 kV E stiiv;Kaycee ere Osagd
345kVE reling Tttermopcits
ee Is
Baiwates GlenrocWMRdlingHIII Ana depry Mine
1185L 0712Cedar$pongs!5 I /(520 uwiAEOLUSWESTanechevreiw'Lat.
Naughtet1Load Paradse
16
Casper 2 1W
Atta te Amasa East Wyoming
Crrrmey Bur:e esg Pirey ccy
Central
Spor Rool Crees O MW
Wyoming D ony o707tTue TB Flow I a II
Chappel Baruil (2x250 MW)3MK Creek Labar96 no
ToPopelu Mustang 'ShirleyBasm
TroDB ''e Dereap 111 MW
To Tre;isuritirm Aecdus 0706 Ekola FlaisKemmererAEOLUSStad(250 uw!
ughton a Brugger WEST Platte 7 Milt;Hili
(120 +101 MW)McFadden Ridge 2B.5 MW
a¢«aa AEOLUS WEST TTOT 4Bwyectin9LimitSimultaneousL¯¯¯¯¯¯¯¯¯¯NomogramUtahICoorwJa
This process involved tuning transformer and generator parameters such that generators were
producing appropriate reactive power output.Additionally,within the 230 kV transmission
system it was verified that the shunt reactive devices were accurately represented,voltage
profiles were normal,reactive power flows were within normal operating ranges and
transmission system voltage was maintained to match acceptable PacifiCorp Transmission
Voltage Schedules.
4 Path Studies
4.1 Aeolus West vs.TOT 4B
Based on the assumptions outlined above,the study demonstrated that the Aeolus West
maximum transfer capability limit is 1792 MW,while meeting all NERC and WECC
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Transfer Capability Assessment
performance criteria.While this transfer level is 832 MW above the present TOT 4A (960
MWl3)path limit for similar conditions,east to west transfers have effectively increased by
914.5 MW due to shiftingthe Platte area load (82.5 MW)east of the Aeolus West cut plane.
The Aeolus West path was stressed by using 3351 MW of total generation resources,which
includes thermal (Dave Johnston,717 MW -net),existing wind (1124 MW),and new wind
(1510 MW)resources.The 240 MW of new wind resource in Big Horn Basin was varied with
Wyodak generation.It was assumed that only the thermal generation at Dave Johnston (717
MW,new)generating plant in eastern Wyoming would be adjusted to maintain transfers on
the Aeolus West transmission path.
The maximum flow limitation of 1792 MW was achieved by utilizingall new and existing
wind resources.
Table 1:Aeolus West and TOT 4B Corner Point Cases (See Figure 3)
Case TOT 4A TOT 4B LimitingElement Outage
(MW)(MW)
1 1792 99 Platte-Latham 230 kV linel4 Anticline -Aeolus 500 kV
line outage with RAS
2 1789 251 Platte-Latham 230 kV linel4 Anticline -Aeolus 500 kV
line outage with RAS
3 1346 840 Yellowtail -Sheridan 230 kV N-0
line
Dave Johnston South Tap -Dave Johnston-Casper
Refinery Tap 115 kV line 230 kV line or Casper -
Spence 230 kV line.
Casper circuit breaker
failure lH40000 or
lH4001.
See Appendix C for power flow diagrams.
In the study,one remedial action schemes (RAS)were considered for N-1 outages:
i.Aeolus RAS to trip up to 627.5 MW of wind generation depending on pre-outage flow
conditions for any of the new transmission element outages between Aeolus -Jim
Bridger.
Figure 3 depicts that the Aeolus West and TOT 4B path interaction is minimized with the
addition of the D.2 Project,as indicated by the straight line (implying no path interaction)when
13 Maximum nomogram point with normal open point at Platte and the dynamic line rating on Platte -Standpipe
230 kV line is utilized
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TOT 4B flows are below 250 MW.As the TOT 4B path flows increases above 250 MW the
nomogram curve becomes resource limited until TOT 4B flow is 840 MW as compared to
present TOT 4A/TOT 4B interaction.However,anytime the emergency dynamic line rating
on Platte -Standpipe is lower than 651 MVA14 the nomogram in Figure 3 might shift to the
left.Therefore,a new system operating limit (SOL)value will be identified to represent the
real time rating restriction to the path.Additionally,the load at Platte substation can cause a
shift in the nomogram;higher load at Platte can shift the curve towards the right and lower
load at Platte can shift the curve towards the left,making it more conservative.This is due to
the Platte -Latham 230 kV line being the limitingelement,as mentioned in Table 5.
Figure 3:Aeolus West Vs TOT 4B Nomogram
Wyoming SystemOperating Curve
2022 HeavyWinter Loads
Normal Open Point:Platte115 kV
900
800
700
2 600
soo Preliminary nomogram,
400 Subject to follow-on
soo analysis.o 200
100
0
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Aeolus West Flow (MW)
4.2 Base Case Development
The 2021-22 HW WECC case was modified to simultaneously stress the Aeolus West and the
TOT 4B path flows.The Aeolus West path was stressed using all of eastern Wyoming resource
from a total of 3111 MW (existing and future)wind and net coal resource.These resources
were re-dispatched with Jim Bridger and Utah Valley resources such that the Jim Bridger West
flows were maintained at 2400 MW.No additional resources were imported from WAPA into
14 The highest loading on the Platte -Standpipe 230 kV line as per power flow analysis based on study assumption.
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PACE system to stress the Aeolus West path.The Shiprock,San Juan and Gladstone phase
shifters were locked to regulate flow across the TOT 3 path between Colorado and Wyoming.
The TOT 4B path flows were adjusted between a minimum of 100 MW and a maximum of
840 MW.The Montana resources,up to 591 MW,were re-dispatched with WAPA (Dry Fork)
to reduce TOT 4B flow or re-dispatched with PAC resources to increase the TOT 4B flow
using Crossover,Rimrock and Steam Plant phase shifters in Montana.
4.3 Transient StabilityAnalysis
Dynamic stability studies evaluating a wide range of system disturbances are under way and
will be presented in a follow-on technical report.
5 Sensitivity Analysis
No additional sensitivity analysis were performed as part of this assessment.
6 Study Conclusions
Technical studies demonstrated that with the addition of the planned D.2 Project facilities to
the Wyoming transmission system,system performance will meet all NERC and WECC
performance criteria.
Updated power flow studies demonstrate that by utilizing existing and planned southeast
Wyomingresourcess,the Aeolus West transmission path can transfer up to 1792 MW under
simultaneous transfer conditions with the TOT 4B transmission path,effectively6 increasing
the east to west transfer levels across Wyoming by 914.5 MW.Power flow findings also
indicated:
Dynamic voltage control is necessary at the Latham 230 kV substation to mitigate low
voltage conditions resulting from loss of Bridger/Anticline -Aeolus transmission
facilities.
Under certain operating conditions,one Remedial Action Schemes (RAS)will need to
be implemented to trip generation followingoutage of specific transmission facilities.
The location (and output level)of new and repoweredwind resources can influence the
transfer capability level across the Aeolus West transmission path,the Aeolus West
and TOT 4B nomogram curve and the area under the nomogram curve.
Dynamic stability studies evaluating a wide range of system disturbances are under way and
will be presented in a follow-on technical report.
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Updated
Aeolus West Transmission Path
Transfer Capability Assessment
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