20180410PAC to Staff UT Attach Aeolus West Transmission.pdf

Aeolus West Transmission Path
Transfer Capability Assessment
Updated Study Report
Revision 2.1
March 30,2018
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...........................................................................................5
2.1 Thermal Loading ...................................................................................................5
2.2 Steady State Voltage Range .............................................................................6
2.3 Post-Transient Voltage Deviation.....................................................................7
2.4 Dynamic Stability Analysis Criteria .............................................................7
2.5 Dynamic Voltage Response .........................................................................7
3 Base Case Development ......................................................................8
3.1 Base Case Selection ...............................................................8
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.......................................................................15
4.3 Dynamic Stability Analysis.......................................................................16
5 Sensitivity Analysis.............................................................................16
6 Study Conclusions ...............................................................................................17
Appendix A -Path Definitions.................................................................18
Appendix B -Power Flow Plots....................................................................18
Appendix C -Dynamic Stability Results (Case C7)........................................................18
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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 October 31,2020.The D.2 Project is part of
PacifiCorp's Energy Vision 2020 (EV2020)initiative which includes the followingmajor
transmission facilities and network upgrades
to support new wind generation resources:Figure 1:Aeolus West Transmission Path
Aeolus 500/230 kV substation,
Shirley Basin -Freezeout 230 kV line
Aeolus Westloop-in to Aeolus,
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 new
line,__-----------
I 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 the Aeolus West transmission path.[Subsequent to the initial announcement,technical studies
have demonstrated that as high as 1,510 MW can be integrated east of the Aeolus West transmission path.]
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 reconductor,
Freezeout -Standpipe 230 kV line reconductor,
Latham dynamic voltage control device,
Separate the double-circuit portion of the Ben Lomond -Naughton 230 kV #1 and Ben
Lomond -Birch Creek 230 kV #2 lines to create two single-circuit lines,
Railroad -Croydon 138 kV partial line reconductor,
Aeolus 230 kV shunt reactor,
Shirley Basin 230 kV shunt reactor,
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 as evaluated
in the Large Generation Interconnection (LGI)queue,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 the Jim Bridger West path,resource
levels in eastern Wyoming were varied relative to the Jim Bridger Generation in central
Wyomingand the Emery/Hunterand Huntingtongenerationin 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 northern Wyoming transmission system contingencies
performed as part of the TPL-001-4 annual assessment.
For this 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 throughoutthe
study.Subsequent transfer capability assessments will evaluate interaction with TOT 3 (Path
36),Bonanza West (Path 33)and TOT lA (Path 30)transmission paths.(See Appendix A.)
In this revision of the report,the power flow analysis was re-evaluatedto identify maximum
transfer capability by stressing both the Aeolus West and the TOT 4B paths simultaneously.If
required,additional power from Western Area Power Administration (WAPA)was imported
into the PacifiCorp East (PACE)balancing authorityarea.
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Conclusions
Technical studies have demonstrated that the interconnected Bulk Electric System (BES)in
Wyoming with the D.2 Project added can support the PacifiCorp 2017R RFP Shortlist
resources,and that system performance will meet all North American Electric Reliability
Corporation (NERC)and Western Electricity Coordinating Council (WECC)performance
criteria.
Preliminary power flow studies demonstrate that by utilizingexisting and planned southeast
Wyomingresourcess,the Aeolus West transmission path can transfer up to 1829 MW under
simultaneous transfer conditions with the TOT 4B transmission path,effectively6 ÏRCTORSÏDg
the east to west transfer levels across Wyoming by 951 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 Scheme (RAS)will need to
be implemented to trip generation followingoutage of specific transmission facilities
in southeast Wyoming.
The location (and output level)of new and repoweredwind resources can influence the
transfer capability level across the Aeolus West transmission path and the Aeolus West
vs.TOT 4B nomogram curve.
Dynamic stability studies evaluated a wide range of critical system disturbances in eastern
Wyoming.The analyses identified two outages with poor voltage performance,and another
outage identified a wind turbine modeling problem.These issues are all attributed to the wind
turbine models at the Q0706,Q0707 and Q0708 projects.PacifiCorp is workingwith the wind
turbine manufacture to resolve these issues.Aside from these issues,the studied outages
evaluatedmeet the dynamic performance criteria with the system being stable and damped.
6 Eastern Wyoming Resources:Existing Wind:1124 MW,Dave Johnston (net)717 MW;Wyodak (PacifiCorp -
net)268 MW,New Wind -behind the Aeolus West "cut plane":1510 MW;east Wyoming:1270 MW,north
Wyoming:240 MW.
6 Effectivetransfers were determined by subtracting the existing TOT 4A path maximuml3 transfer level (960
MW)from the Aeolus West transfer level (1829 MW)and adding the Platte area loads (82 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 any necessary Remedial Action Schemes (RAS).
This report will summarize the results of the power flow and dynamic stability analysis of the
Aeolus West transmission path and will demonstrate that Wyoming transmission system
performance with the D.2 project added meets all NERC and WECC performance criteria.
1.2 Plan of Service
The D.2 Project,and supporting network upgrades consists of the following system
improvements:
1.Add Aeolus 500/230 kV substation
2.Add Aeolus 500/230 kV,1600 MVA transformer
3.Loop the Shirley Basin -Freezeout 230 kV line into Aeolus,
4.Add Anticline 500/345 kV substation
5.Add Anticline 500/345 kV,1600 MVA transformer
6.Add the Aeolus -Anticline 500 kV transmission line,137.8-miles,3x1272 ACSR
(Bittern)conductor
7.Add the Anticline -Bridger 345 kV line,5.1-miles,3x1272 ACSR (Bittern)conductor
8.Add the Aeolus 230 kV,60 MVAr shunt reactor
9.Add the Shirley Basin 230 kV,60 MVAr shunt reactor
10.Add Aeolus 500 kV,200 MVAr shunt capacitor
11.Add Anticline 500 kV,200 MVAr shunt capacitor
12.Rebuilding of the Aeolus -Shirley Basin 230 kV #1 line,2xl557 ACSS/TW
(Hudson/TW)conductor
13.Add the Aeolus -Shirley Basin 230 kV #2 line,2xl557 ACSS/TW (Hudson/TW)
conductor
14.Reconductor the Aeolus -Freezeout 230 kV line,2x1272 ACSR (Bittern)conductor
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15.Reconductorthe Freezeout -Standpipe 230 kV line,2x1272 ACSR (Bittern)conductor
16.Add dynamic reactive device at Latham 230 kV substation.
17.Separate eight miles of the double-circuit Ben Lomond -Naughton 230 kV #1 and Ben
Lomond -Birch Creek 230 kV #2 lines to create two single-circuit lines,and
18.Reconductor 2.35 miles of the Railroad -Croydon 138 kV line,1222 ACCC high
temperature conductor,
1.3 Planned OperatingDate
The in-service date for all facilities associated with the D.2 Project is October 31,2020.
1.4 Scope
The Aeolus West transfer capability assessment assumes the addition of new wind generation
facilities as noted in Table 1,which includes the PacifiCorp 2017R RFP Shortlist resources as
evaluated in LGI queue studies.While the new technology and model information of the
repowered units was used in the steady-state and dynamic stability analysis,no incremental
MW output was considered;i.e.,each repowered facility was limited to its current LGI
agreement generationcapacity levels.The study was performed using a 2021-22 heavy winter
WECC approved case which was modified to include the D.2 Project 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 l 15 kV normallyopen is presently the most
limitingscenario for the existing TOT 4A/4B nomogram.
2 Study Criteria
2.1 Thermal Loading
For system normal conditions described by the P0'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.
7 Facility outage events that are identifiedwith "P"designations are referenced to the TPL-001-4 NERC standard.
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The thermal ratings of PacifiCorp's BES transmission lines and transformers are based on the
most recent PacifiCorp's Weak Link Transmission Database and Weak Link Transformer
Database.
Table 1:Generating Resources Studied
Existing Wyoming Thermal Existing East New WyomingWind
Generation WyomingWind Generation
Generation
2396 MW 1124 MW 1731 MW
Dave Johnston (DJ):717 MW (Foote Creek,Rock Eastern Wyoming (Aeolus,
Wyodak (PacifiCorp):268 River,High Plains,Shirley Basin,Windstar):
MW Seven Mile Hill,1270 MW
Jim Bridger (PacifiCorp):Dunlap,Root Creek,Northern Wyoming
1411 MW Top of the World,(Bighorn Basin):240 MW
Glenrock,Three Southwest Wyoming(Uinta
Buttes,Chevron)County):221 MW
See Table 4.
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.
Table 2:Voltage Criteria
ContingencyConditionsOperatingSystemNormalConditions(PO)(P1-P7)Configuration
Vmin (pu)Vmax (pu)Vmin (pu)Vmax (pu)
Looped 0.95 1.069 0.90 1.10
Radial 0.90 1.06 0.85 1.10
8 PacifiCorp Engineering Handbook "Planning Standards for Transmission Voltage,"April 8,2013.
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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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 P0 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 Dynamic StabilityAnalysis Criteria
All voltages,frequencies and relative rotor angles are required to be stable and damped.
Cascading or uncontrolled separation shall not occur and dynamic voltage response shall be
within established limits.
2.5 Dynamic Voltage Response
Dynamic stability voltage response criteria are based on WECC Regional Performance Criteria
WRl.3 through WRl.5 as follows:
Dynamic 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
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:
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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.
3 Base Case Development
3.1 Base Case Selection
The base case developmentprocess involves selecting an approvedWECC base case,updating
the models to represent plannedtransmission facilities (D.2 Project)and existing and new wind
generation(see Table 1)facilities,and then tuning the cases to maximum transfer levels on the
WECC transmission path(s)being studied.For this study,the WECC approvedbase case 2021-
22 HW (created on August 19,2016)was selected.This case meets key criteria in that it is
close to the Projects'in-service date of October 31,2020,includes average load conditions
based on 2021 load projections and has an accompanying dynamic stability base case available.
This study focused on simultaneous transmission path interaction in the Wyoming area
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Transfer Capability Assessment
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 selected from the 2021-22 HW base
case are listed below:
Table 3:Wyoming Load,Generation and Platte Normal Open Configuration in Base Case
Load or Generation Amount (MW)
North Wyoming PAC Load (includingWyodak load 391 MWof42MW)
North Wyoming -WAPA Load 211 MW
Eastern WyomingPAC Load (includingDJ load of 56 474 MWMW)
Eastern Wyoming PAC Loads on WAPA System 95 MW
Central WyomingLoad (includingJB load of 130 434 MWMW)
Yellowtail South Flow 192 MW
Yellowtail Generation 140/260 MW (Online/Max)
WAPA's Existing Small Generationl°in North .
.26/50 MW(Online/Max)Wyoming
WAPA's Existing Small Generationil in Eastern .
.484/584 MW(Online/Max)Wyoming
Wyodak Generation (PacifiCorp/Black Hills)350/380 MW (Online/Max)
Dry Fork Generation (Basin Electric)420/440 MW (Online/Max)
Gross Laramie River Generation I (WAPA's swing
.605 MW(Max)machme)
io WAPA's small generation in north Wyoming includes;Boysen,Buffalo Bill,Heart Mountain,Shoshone,
Spring Mountain
"WAPA's small generation in eastern Wyoming includes;Alcova,Fremont,Glendo,Guernsy,Kortes,Seminoe,
CLR_l,SS_Genl AND CPGSTN
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Transfer Capability Assessment
Load or Generation Amount (MW)
Gross Laramie River Generation II 590/605 MW(Online/Max)
Gross Dave Johnston (DJ)Generation 700/774 MW(Online/Max)
Total Existing PAC East WyomingWindl2 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 Flow 627 MW
TOT 4B Flow 469 MW
Jim Bridger (JB)Generation 2200 MW
Jim Bridger West Flow 2027 MW
TOT 3 Flow 1259.1 MW
TOT lA Flow 195 MW
Platte -Mustang 115 kV Normal Open Point Platte -Normal Open
3.2 Generating FacilityAdditions
The transmission path assessment studies outlined in Section 4 were performed by utilizing
the resources identified in Table 4 to evaluate the performance of the Aeolus West transmission
path.Transmission and generationprojects with an in-service date beyond 2020 were excluded
from the analysis.While Table 4 provides the general location of the resources included in the
study,Figure 2 provides an overview of PacifiCorp's Wyoming transmission system and
provides a visual illustration of the location of each of the existing and new generation (noted
in red)resources,and identifies the location of the Aeolus West and TOT 4B transmission path
constramts.
12 PAC eastern Wyoming wind generation includes;Root Creek,Three Buttes,Top of The World,Glenrock,
Rolling Hills,Dunlap.Seven Mile Hill,Foote Creek and High Plains wind generation
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Table 4:New Wyoming Wind Resources
LGIProposedNew ProjectQueue Point of InterconnectionWindFacilitiesSizeNumber
Northern Wyoming ..
.Q542 240 MW Franme -Yellowtail 230 kV lme(Bighorn Basm)
-Q706 250 MW Aeolus 230 kVEasternWyommg
(Aeolus/Shirley Q707 250 MW Shirley Basin 230 kV
Basin/Windstar Q708 250 MW Shirley Basin 230 kV
Area)Q712 520 MW Windstar 230 kV
Southwest Wyoming Q715 120 MW LanyonCompression -Railroad 138 kV
(Uinta County)Canyon Compression -Railroad 138 kVQ810101MW.lme
TOTAL 1731 MW
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 generation 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 maximizing the 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 capacity levels.The additional generation in southeast
Wyoming was displaced with Jim Bridger,central and southern Utah generation.The Jim
Bridger generation output was maintained such that Jim Bridger West path flows were
maintained near 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
system of wind generationfacilities were below 1.05 p.u.and that there was no reactive power
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GSU loop flow conditions for wind generation facilities that have multiplemain generator
step-up GSU transformers.
Figure 2
Existing/Proposed Wyoming Generation Resources,and Transmission Constraints
Bo r ts Yellowtail
Montana Decker Wyomont Montana
PacifiCorp
Aeolus West/TOT4B Wyoming
TransmissionConstraints cariana i
DryFork i
OregonBasin NorthWyoming
271sM NT Lookout
Buffalo DCa"Hughes
GrassCreek TOT4B Ba er cr k
<230 kV Existing Kaycee Reno Osage
230 kV Existing
345 kV Existing Thermopolls P pkin I
----500kVProposed Badwater Midwest Glenr klRolLng "
eaYellowca
e Q712Cedarspringsl (520
AEOLUS WEST Riverton ChevronWind Latigo Windstar
Wyopo 16 5 MW TOW
Naughton Load Paradise e/,
casper
811 1w 200 2 Mw
s#EastWyoming
Atlanticcity Spence Amasa
ChimneyButte BigPiney
i
dh Central RootCreek80MW
Wyoming Dif5culty Q707/708 TBFiats I&II (2x250
To3MK ee Labarge ao Bairoi!MW)
ToPopulu Mustang 0409 Shirley Basin
Trona Boswell springs Dunlap 111 MW
ToTreasureton 'N Aeolus
Kemmerer //AEOLUS standpip 3 Freezeout
o70eEkolaFiats(250
aug n
Palisdes '
tcirne WEST Platte 7Miie 118.5
i Birchereek Man nt FooteCreek 135MW
C Comp FireholeToBenLomondQ715/8101Ulinta II(120 (simpiou Mendhd
i e 8
WMW
Railroad Wyoming AEOLUS WEST ffOT 4B Limit1.--.--wouww.....,__.__.__._,__._SimultaneousNomogram
Utah !Colorado
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 1829 MW,while meeting all NERC and WECC
performance criteria.While this transfer level is 869 MW above the present TOT 4A (960
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Transfer Capability Assessment
MWl3)path limit for similar conditions,east to west transfers have effectively increased by
951 MW due to shifting the Platte area load (82 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 as necessary.It was assumed that only the thermal generation at Dave
Johnston and Wyodak generating plants in eastern Wyomingwould be adjusted to maintain
transfers on the Aeolus West and the TOT 4B transmission paths.
Table 5:Aeolus West and TOT 4B Corner Point Cases (See Figure 3)
Case Aeolus TOT 4B Limiting Element Outage
West (MW)
(MW)
1 1829 100 Platte-Latham 230 kV line Anticline -Aeolus 500
kV line outage with
RAS
2 1803 300 Platte-Latham 230 kV line Anticline -Aeolus 500
kV line outage with
RAS
3 1777 500 Platte-Latham 230 kV line Anticline -Aeolus 500
kV line outage with
RAS
4 1763 607 Platte-Latham 230 kV line Anticline -Aeolus 500
kV line outage with
RAS
Dave Johnston South Tap -Casper 230 kV CB
RefineryTap -Casper 115 1H4001 failure causing
kV line Casper -Dave Johnston
230 kV and Casper
230/115 kV transformer
outage or Casper -Dave
Johnston 230 kV line
outage
5 1628 699 Platte-Latham 230 kV line Anticline -Aeolus 500
kV line outage with
RAS
13 Maximum nomogram point with normal open point at Platte utilizing the dynamic line rating on Platte -
Standpipe 230 kV line.
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Case Aeolus TOT 4B Limiting Element Outage
West (MW)
(MW)
Dave Johnston South Tap -Casper 230 kV CB
RefineryTap -Casper 115 lH4001 failure causing
kV line Casper -Dave Johnston
230 kV and Casper
230/115 kV transformer
outage or Casper -Dave
Johnston 230 kV line
outage
6 1125 880 Yellowtail -Sheridan 230 kV N-0
line
See Appendix B for power flow plots.
The low voltage issue in the Big Horn Wyoming area is an existing issue for the Yellowtail -
Frannie 230 kV line outage or future Q0542 POI -Frannie 230 kV outage.This issue is
resolved by adding capacitor banks at various locations in north Wyoming.A project to install
a new 30 MVAr shunt capacitor bank at Grass Creek 230 kV,two new 20 MVAr shunt
capacitor banks at Frannie and a new 7.5 MVAr capacitor bank at Hilltop115 kV are proposed.
In the study,one RAS scheme was identified for N-1 outages:
i.Aeolus RAS to trip approximately 630 MW of wind generation depending on pre-
outage flow conditions for any of the new transmission element outages between
Aeolus -Jim Bridger.
Study results are summarized in Table 5 and illustrated in Figure 3.In reviewing Figure 3,it
is evident that the Aeolus West and TOT 4B path interaction are minimized with the addition
of the D.2 Project,as indicated by the straight horizontal line (implying no path interaction)
when Aeolus West flows are below 1125 MW.The Aeolus West vs TOT 4B nomogram "knee
point"is at Aeolus West flows of 1763 MW (TOT 4B,607 MW).As TOT 4B flows increase
from that point,Aeolus West flows reduce;likewise,from the knee point as TOT 4B flows
decrease,Aeolus West flows increase.
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Transfer Capability Assessment
Figure 3:Aeolus West Vs TOT 4B Nomogram
Wyoming System Operating Curve
2022 Heavy Winter Loads
Normal Open Point:Plattell5 kV
Aeolus West Vs TOT 4B Nomogram
1000 1125,880
900
N00
"00 1628,699
00 1763,607
500 1777,500
200
100 1829,100
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 and north
Wyomingresources fora total of 3619 MW (existing and future)wind and net coal resources.
These resources were displaced with Jim Bridger and resources in central and southern Utah
such that the Jim Bridger West flows were maintained near 2400 MW.
The TOT 4B path flows were adjusted between a minimum of 100 MW and a maximum of
880 MW.Additional resources were exported from PACE to Montana and WAPA to Montana
to adjust flows across the TOT 4B path between 300 MW and 880 MW using Crossover,
Rimrock and Steam Plant phase shifting transformers in Montana.
The Shiprock,San Juan and Gladstone phase shifting transformers were locked to regulate
flow across the TOT 3 path between Colorado and Wyoming.
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4.3 Dynamic StabilityAnalysis
The dynamic stability analysis was performed using PSS/E models provided by both General
Electric (GE)and Vestas's for the repowered and new wind generation.The generic model for
the Root Creek wind model was updated to the GE0501 model (GE 1.85 units).Top of the
World and Three Buttes wind farms in eastern Wyoming were updated to the GE 1.5 wind
turbine model provided by GE for PTI V33.A generic WECC model was used for the Latham
dynamic reactive device.
The stability study was focused in the eastern Wyomingregion to demonstrate the acceptable
performance from various new wind farms in the region.The real power,reactive power and
voltage output from the new and the existing wind farm generators were reviewed to evaluate
their ability to support the transmission grid voltage and system stability during various outage
scenarios.Due to the combination of different wind turbine models,dynamic analysis also
ensured that no interaction issues were being observed.
The dynamic stability study was performed for one (worst case)nomogrampoint on the Aeolus
West vs.the TOT 4B nomogram curve,which reflected the heaviest Aeolus West flow
conditions.
Dynamic stability analysis was performed on selective critical outages based on anticipated
post fault impacts on the wind generationperformance,especially for the portion of the system
with a calculated short circuit ratio of approximately 2.3.See Appendix C for the dynamic
stability analysis summary and dynamic plots.
5 Sensitivity Analysis
The sensitivity analysis focused on the evaluation of two different RAS generation tripping
scenarios to ascertain which scheme would be the most effective at tripping generation
followingoutage of the D.2 Project facilities between Bridger and Aeolus.
A dynamic stability sensitivity analysis was performed to evaluate the system impact and
generator performance for a single element outage on the D.2 segment between Aeolus 230
kV and Bridger 345 kV buses which requires a RAS for generator tripping.Two different sets
of generator tripping locations and tripping levels (approximately 630 MW)were selected.The
generation tripping of 607 MW,which includes High Plains,Seven Mile Hill,Q706 and
Dunlap wind generation was compared with generation tripping of 628 MW,which includes
High Plains,Q0706 and Q0707 wind generation.For summary results and plots,please see
dynamic simulation cases la -lf2 in Appendix C.
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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 1829 MW under
simultaneous transfer conditions with the TOT 4B transmission path,effectively6 ÏRCTORSing
the east to west transfer levels across Wyoming by 951 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 RAS scheme will need to be implemented to
trip generation followingthe outage 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 evaluated a wide range of critical system disturbances in eastern
Wyoming.The analyses identified two outages with poor voltage performance,and another
outage identified a wind turbine modeling problem.These issues are all attributed to the wind
turbine models at the Q0706,Q0707 and Q0708 projects.PacifiCorp is workingwith the wind
turbine manufacture to resolve these issues.Aside from these issues,the studied outages
evaluatedmeet the dynamic performance criteria with the system being stable and damped.
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Report Appendices
Appendix A -Path Definitions
Appendix B -Power Flow Plots
Appendix C -Dynamic Stability Results (Case C7)
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