BHBE-G7 Feasibility Study 040108

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GENERATOR INTERCONNECTION REQUEST

BHBE-G7Interconnection Feasibility Study

PREPAREDBY

BLACK HILLS POWER

TRANSMISSION PLANNING

April 1, 2008


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Table of Contents

Executive Summary .......................................................................................................................... 41 Background ............................................................................................................................... 6

1.1 Study Objective................................................................................................................... 6

1.2 Project Description ............................................................................................................. 61.3 Modeled Layout .................................................................................................................. 82 Study Area ................................................................................................................................. 9

2.1 Transmission System .......................................................................................................... 93 Base Case Development ............................................................................................................ 9

3.1 Base Case Origin and Year................................................................................................. 93.2 Area Load ........................................................................................................................... 93.3 Planned Projects.................................................................................................................. 93.4 Analytical Tools................................................................................................................ 10

4 Steady State Analysis Methodology ...................................................................................... 104.1 Steady State Analysis Methodology ................................................................................. 10

4.1.1 Voltage Limits .......................................................................................................... 104.1.2 Thermal Limits ......................................................................................................... 104.1.3 Solution Parameters .................................................................................................. 11

4.2 Case Naming Convention ................................................................................................. 114.3 Steady State Contingency List.......................................................................................... 134.4 Steady State Base Case Dispatch and Interface Conditions ............................................. 14

5 Steady State Analysis Results ................................................................................................ 145.1 Light Winter Pre-Wind Results ........................................................................................ 155.2 Light Winter Energy Resource Results ............................................................................ 155.3 Light Winter Network Resource Results .......................................................................... 155.4 Heavy Summer Pre-Wind Results .................................................................................... 155.5 Heavy Summer Energy Resource Results ........................................................................ 155.6 Heavy Summer Network Resource Results...................................................................... 15

6 Stability Analysis Methodology ............................................................................................. 166.1 Stability Testing Methodology ......................................................................................... 16

6.1.1 Stability Performance Criteria .................................................................................. 166.1.2 Low Voltage Ride Through Criteria......................................................................... 16

6.2 Stability Base Case Dispatch and Interface Conditions.................................................... 166.3 Stability Fault Descriptions .............................................................................................. 16

7 Stability Analysis Results ....................................................................................................... 178 TOT 4A/4B Analysis ............................................................................................................... 17

8.1 TOT 4A/4B Analysis Procedure....................................................................................... 178.2 TOT 4A/4B Analysis Results ........................................................................................... 19

9 Short Circuit Analysis ............................................................................................................ 199.1 Short Circuit Study Modeling........................................................................................... 199.2 Short Circuit Analysis Results.......................................................................................... 209.3 Short Circuit Analysis Conclusion ................................................................................... 22

10 Conclusions .......................................................................................................................... 22

____________________________________________________________________________________________________________BHBE-G7 Black Hills PowerInterconnection Feasibility Study Report April 1, 2008

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Appendices

APPENDIX A: Preliminary One Line Diagrams of Proposed Wind Farm...................................... 24

List of Tables

Table 1: Proposed Project Generator Modeling Data......................................................................... 6Table 2: Proposed Project Collector Data........................................................................................... 6Table 3: Proposed Project Transformer Modeling Data..................................................................... 7Table 4: Steady State Voltage Criteria ............................................................................................. 10Table 5: Steady State Solution Parameters ....................................................................................... 11Table 6: Pre-Wind Prior Outage List................................................................................................ 12Table 7: Post-Wind Prior Outage List .............................................................................................. 12Table 8: Pre-Wind Scenario Contingency List ................................................................................. 13Table 9: Post-Wind Scenario Contingency List ............................................................................... 14

Table 10: Stability Fault Descriptions .............................................................................................. 16Table 11: TOT 4A/4B Study Contingency List................................................................................ 18Table 12: Pumpkin Buttes-Teckla POI Fault Results....................................................................... 21Table 13: Pumpkin Buttes POI Fault Results ................................................................................... 21Table 15: Pumpkin Buttes-Teckla 230 kV Line POI Costs.............................................................. 22Table 16: Pumpkin Buttes 230 kV Substation POI Costs ................................................................ 22

List of Figures

Figure 1: Modeled Layout of Proposed Project.................................................................................. 8

Figure 2: Case Naming Convention.................................................................................................. 11Figure 3: TOT 4A/4B Analysis Results............................................................................................ 19


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Executive Summary

Black Hills Power conducted an Interconnection Feasibility Study (FS) under the guidance of the Common Use System(CUS) Open Access Transmission Tariff Large Generator Interconnection Procedures (LGIP) for the interconnectioncustomer to construct and interconnect a 500 MW wind farm in northeast Wyoming. The proposed project consists ofthree hundred thirty-four (334) 1.5 MW GE wind turbine generators and will connect to the CUS 230 kV transmission

system at or near Pumpkin Buttes substation in Campbell County, Wyoming. The initial interconnection date for the project is September 2010.

The study was performed as a Feasibility Study (FS) based upon the information set forth in the signed InterconnectionRequest dated September 25, 2007.

The purpose of the study was to:(i) Analyze the steady-state and short circuit conditions for the project(ii) Evaluate limited worst-case stability performance(iii) Determine any upgrades to the transmission system that would be required to mitigate any adverse

impacts that the proposed project could otherwise pose on the reliability and operating characteristics ofthe transmission system .

(iv) Determine any upgrades required to mitigate any degradation to transmission transfer capability.

The primary area of concern for this study is northeast Wyoming. The proposed project is to be interconnected at anew switching station on the Pumpkin Buttes-Teckla 230 kV line. The Pumpkin Buttes 230 kV substation wasevaluated as an alternative Point of Interconnection (POI). The project was evaluated as both an Energy Resource andas a Network Resource

Steady-State AnalysisSteady-state voltage and thermal analyses examined system performance without the proposed project in order toestablish a baseline for comparison. System performance was re-evaluated with the project in place and compared withthe baseline performance to demonstrate the impact of the project on local transmission reliability.

If the project was interconnected at a tap bus on the Pumpkin Buttes-Teckla 230 kV line, a second 230 kV circuit fromthe tap bus to the Pumpkin Buttes substation would be required to prevent thermal overload issues. Costs of this lineare dependent on the location of the tap bus relative to Pumpkin Buttes. Total costs of interconnecting on the PumpkinButtes-Teckla 230 kV line were estimated at $6,318,000. These costs include a new 230 kV five-terminal substation, asecond 230 kV circuit connected from the POI to Pumpkin Buttes, and the addition of a new bay in the Pumpkin Buttessubstation.

Interconnecting directly to the Pumpkin Buttes substation would require a new bay in the Pumpkin Buttes substation atan estimated cost of $1,000,000.

The interconnection of the proposed 500 MW project as an energy resource would require additional transmissioncapacity to deliver the energy outside the study area. Identifying the best transmission alternative is dependent on thesize of the project and the point-of-delivery for the resource. A 150-mile 230 kV path from Carr Draw to Tongue Riverto Yellowtail was modeled to provide a generic solution to the issues encountered in the study. The upgrade of a single115 kV line in the study area was also required to accommodate the proposed 500 MW project. Total costs for theseupgrades were estimated at $44,480,000.

The required upgrades would be limited to the Dave Johnston-Dave Johnston South Tap 115 kV line if the nameplaterating of the project was reduced to 250 MW. Cost estimates for this configuration were approximately $280,000.

No additional transmission system upgrades were identified in order to interconnect the proposed project as a networkresource.

Stability Analysis


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Stability cases evaluated the impact of the proposed project on transmission system performance for the light winterload level, as high energy exports and lower load levels present a worst-case model. Several wind dispatch scenarioswere utilized during the stability analysis.

The stability analysis identified the projects impacts on the transmission system following several differentdisturbances and verified the projects Low Voltage Ride-Through (LVRT) capability was in accordance with thecurrent FERC LVRT standard. Stability analysis results showed that no reliability criteria were violated as a result ofthe proposed interconnection.

TOT 4A/4B AnalysisThe proposed project as studied was located in close proximity to the TOT4A and TOT4B paths. Steady state analysiswas performed to determine any adverse impacts on the established path operating limits. The results of the analysisverified that there were no negative impacts to TOT4A and TOT4B as a result of interconnecting the proposed wind

plant.

Short Circuit AnalysisShort circuit analysis was performed during the FS to assess the impact of the proposed project on the fault currentlevels and breaker duty in the area. The surrounding breakers were evaluated to determine if the additions to thetransmission system created any breaker over-duty conditions. No adverse short circuit impacts were identified as aresult of interconnecting the proposed project.

ConclusionThe interconnection Feasibility Study identified no necessary upgrades to the local transmission system if the proposed

project was interconnected as a Network Resource.

If the project proceeds with Energy Resource Interconnection Service, the maximum nameplate output of the projectwould be limited to 250 MW to prevent thermal overloads on the surrounding transmission system. Upgradesnecessary to accommodate the entire 500 MW project as an energy resource were estimated at $44,480,000.

Approximate costs of the interconnection on the Pumpkin Buttes-Teckla 230 kV line were $6,318,000. Approximatecosts of the Pumpkin Buttes interconnection were estimated at $1,000,000. These costs are separate from the upgradecosts associated with the Energy Resource interconnection.

Interconnection Service in and of itself does not convey any right to deliver electricity to any specific customer or Pointof Delivery. Curtailment of the proposed interconnection project may be necessary under certain emergency operatingconditions.


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1 Background

1.1 Study ObjectiveThe primary objective of the study was to determine whether the proposed interconnection had any adverse impactson the reliability, stability or operating characteristics of the Bulk Power System (BPS). Steady-state and short-circuit conditions were analyzed in this study. Additionally, limited worst-case stability performance wasevaluated.

1.2 Project DescriptionThe proposed project consists of three hundred thirty-four (334) 1.5 MW GE wind turbine generators, producing upto 500 MW total. The project was studied as both a network resource and an energy resource, interconnected ateither a new switching station on the Pumpkin Buttes-Teckla 230 kV line or directly to the Pumpkin Buttes 230 kVsubstation.

The Project as modeled consists of the following electrical components and construction activities: Construct a 230 kV substation estimated to be 5.6 miles from the Pumpkin Buttes 230 kV substation.

Alternatively, the project would tie directly into the Pumpkin Buttes substation. Install four 230/34.5 kV transformers that will connect the 34.5 kV collector system feeders directly to a 230

kV bus, which will also be located at the projects substation. Construct 333 wind turbine generators (WTGs) operating at 575 V nominal, each equipped with its own

dedicated 575 V: 34.5 kV generator step-up transformer (GSU). The change in the number of WTGs from334 to 333 was per the modeling data submitted by the Interconnection Customer.

Construct four collector buses operating at 34.5 kV nominal; each bus consisting of approximately 83 GE 1.5MW wind turbines. The collector buses will tie into one 34.5 kV main collector bus in the projects 230 kV:34.5 kV substation.

1.2.1 Technical SpecificationsTables 1-3 list the technical specifications as provided by the interconnection customer.

Table 1: Proposed Project Generator Modeling Data

Proposed Project Generator Modeling Data Referenced From Low Side of GSU

Power Factor RangeType Individual UnitMVA Rating

MW

Lagging Leading Doubly-Fed Induction Generator (DFIG)

1.67 1.5 0.90 0.95

Table 2: Proposed Project Collector Data

Proposed Project Transmission Line DataDescript ion Type Base MVA R (u-Ohm/ft) X (u-Ohm/ft) B (uS/mi)

34.5 kV Collector System 500 MCM 100 0.00 0.0001 0.0001


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Table 3: Proposed Project Transformer Modeling Data

STEP-UP FEEDER PARAMETERS EQUIVALENT GEN PARAMETERS

230/34.5 kV Xfmr Feeder#Length

(mi) R X B# of

Turbines MVA P Qmax Qmin

#1 - rated 75/100/125 MVA 1 1.0 0.024 0.027 0.004 17 28.4 25.5 8.3 -12.4

(x=0.1200 on 100 MVA Base) 2 2.0 0.048 0.053 0.009 17 28.4 25.5 8.3 -12.4

3 0.8 0.018 0.020 0.003 18 30.1 27.0 8.8 -13.1

4 2.5 0.060 0.067 0.011 17 28.4 25.5 8.3 -12.4

5 2.0 0.048 0.053 0.009 17 28.4 25.5 8.3 -12.4Transformer

Total 86 143.6 129.0 42.1 -62.8

#2 - rated 75/100/125 MVA 6 4.5 0.108 0.120 0.020 17 28.4 25.5 8.3 -12.4

(x=0.1200 on 100 MVA Base) 7 3.8 0.090 0.100 0.017 17 28.4 25.5 8.3 -12.4

8 5.5 0.132 0.146 0.024 17 28.4 25.5 8.3 -12.4

9 6.8 0.163 0.181 0.030 16 26.7 24.0 7.8 -11.7

10 8.0 0.192 0.213 0.035 16 26.7 24.0 7.8 -11.7Transformer

Total 83 138.6 124.5 40.7 -60.6

#3 - rated 75/100/125 MVA 11 4.3 0.103 0.114 0.019 17 28.4 25.5 8.3 -12.4

(x=0.1200 on 100 MVA Base) 12 5.5 0.132 0.146 0.024 17 28.4 25.5 8.3 -12.4

13 7.0 0.168 0.186 0.031 17 28.4 25.5 8.3 -12.4

14 7.5 0.180 0.200 0.033 16 26.7 24.0 7.8 -11.7

15 5.8 0.138 0.153 0.026 16 26.7 24.0 7.8 -11.7Transformer

Total 83 138.6 124.5 40.7 -60.6

#4 - rated 75/100/125 MVA 16 6.3 0.151 0.168 0.028 17 28.4 25.5 8.3 -12.4

(x=0.1200 on 100 MVA Base) 17 8.0 0.192 0.213 0.035 16 26.7 24.0 7.8 -11.7

18 9.1 0.218 0.242 0.040 15 25.1 22.5 7.4 -11.0

19 7.8 0.186 0.206 0.034 17 28.4 25.5 8.3 -12.4

20 7.8 0.186 0.206 0.034 16 26.7 24.0 7.8 -11.7Transformer

Total 81 135.3 121.5 39.7 -59.1

Project Total 333 556.1 499.5 163.2 -243.1


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1.3 Modeled LayoutThe project was modeled using lumped equivalent machines as shown in Figure 1. The POI in Figure 1 is a newsubstation on the Pumpkin Buttes-Teckla 230 kV line. The Hartzog 230 kV bus as shown in Figure 1 is synonymouswith the Pumpkin Buttes 230 kV bus. A PSS/E single-line diagram is included in Appendix A.

Figure 1: Modeled Layout of Proposed Project


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2 Study Area

2.1 Transmission SystemThe study area consists of the northeast Wyoming bulk transmission system centered on Campbell County,Wyoming. The study area is bounded by TOT4B to the northwest, TOT4A to the southwest, Laramie River Stationand Stegall to the southeast, and Rapid City to the east.

3 Base Case Development

3.1 Base Case Origin and YearThe base cases originated from the Western Electricity Coordinating Council (WECC) Library as part of the 2007Study Program. The base case for the 2011 heavy summer load scenario was the 11HS1B1P study case. The 2011light load scenario started with the 2011LSP1SA1P study case. These base cases were selected primarily due to theirrecent approval dates with the assumption that the level of accuracy regarding system representation would be higherthan that of an older base case.

3.2 Area Load

3.2.1 2011 Heavy SummerThe 2011 heavy summer load case was created by updating BHP, CLF&P, and Basin Electric loads to their 2011

peak forecast values. Minor load additions were also included for better representation of the northeastWyoming area.

3.2.2 2011 Light WinterThe 2010 light winter load case was created by scaling BHP and CLF&P loads to 55% of 2011 peak summerforecast values, and Basin Electric loads to 75% of 2011 peak winter forecast values. Coal Bed Methane (CBM)loads were scaled to 100% of peak winter forecast values. As in the summer case, minor load additions wereincluded.

3.3 Planned ProjectsSeveral planned projects exist that were deemed relevant to the study and were added to the WECC base cases.

These additions are listed below.

3.3.1 Hughes Transmission ProjectThe Hughes Transmission Project was included in all study cases. The project consists of two phases, the firstof which is a new 230 kV transmission line extending from the existing Hughes 230 kV substation to the newDry Fork 230 kV substation and on to the existing Carr Draw 230 kV substation. The second phase consists of anew 230 kV transmission line from the new Dry Fork 230 kV substation extending north and west to the newTongue River 230 kV switching station and on to the existing PacifiCorp Sheridan 230 kV substation.

3.3.2 Wyodak-Dave Johnston Area 230 kV LineThe project consists of two new 230 kV transmission lines. The first line terminates at the new Donkey Creeksubstation and the Pumpkin Buttes substation. The second line terminates at the Pumpkin Buttes substation and ayet to be determined point in the Dave Johnston area. For purposes of this study the second line was modeled as

terminating at the Dave Johnston 230 kV substation.3.3.3 Teckla Dynamic Voltage SupportTwo 16 MVAR dynamic reactive devices were modeled at Teckla 230 kV substation, one device on eachtertiary winding of the existing 230/69 kV transformers. The existing 15 MVAR capacitors were modeled attheir respective 69 kV bus.

3.3.4 Rapid City Dynamic Voltage Support

____________________________________________________________________________________________________________BHBE-G7 Black Hills Power

A +100/-50 MVAR Static VAr Compensator was modeled on the Lange 230 kV bus.

Interconnection Feasibility Study Report April 1, 20089


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3.3.5 Casper-Dave Johnston Transmission ProjectThe DJ-Spence 230 kV line was looped into the Casper 230 kV substation. The resulting parallel DJ-Casper 230kV lines were re-conductored to maintain TOT 4A/4B nomogram capabilities.

3.3.6 Dave Johnston WindTwo identical 99 MW wind generating projects were modeled at the Dave Johnston 230 kV bus per PaciCorpsrequest.

3.3.7 300 MW Path C UpgradeVarious upgrades were made to the 138 kV lines between Populus and Terminal substations to increase thetransfer capability from Wyoming/Idaho to Utah by up to 300 MW.

3.3.8 Threemile Knoll 345 kV ProjectThe Bridger-Goshen 345 kV line was looped into a new Threemile Knoll 345/138 kV substation. Projectincludes various 115 kV line additions.

Should the any one of the projects listed above not be complete prior to the proposed project in-service date, theInterconnection project may be curtailed due to transmission prior outages or other emergency conditions. Thesecurtailments and/or operating restrictions, if needed, will be developed and identified through operational studies asrequired.

3.4 Analytical ToolsPower flow and dynamic analyses were performed using PSS/E load flow and dynamic simulation software, version30.2.1. Short circuit analysis was performed using ASPEN OneLiner, version 10.9.

4 Steady State Analysis Methodology

4.1 Steady State Analysis MethodologyThe proposed project was evaluated at 2011 peak summer and light winter load levels to determine if it caused anysignificant adverse impact to the reliability and operating characteristics of the WECC bulk transmission system and,more specifically the CUS transmission system. Steady state voltage and thermal analyses examined system

performance without the proposed project in order to establish a baseline for comparison. Performance was re-evaluated with the proposed project in-service and compared to the baseline performance to determine the impact ofthe project on area transmission reliability. The criteria described below are consistent with the WECC MinimumOperating Reliability Criteria and Colorado Coordinated Planning Groups Voltage Coordination Guide.

4.1.1 Voltage LimitsTable 4 identifies the voltage criteria used in or around the primary study area for the steady state voltageassessment. Pre-existing voltage violations outside the localized study area were ignored during the evaluationof the proposed projects impacts.

Table 4: Steady State Voltage Criteria

Acceptable Voltage RangeApplicableControl Area

VoltageClass Pre-Contingency

(normal conditions)Post-Contingency

(emergency conditions)PACE, WAPA-RMR 69 kV and above 0.95 to 1.05 p.u. 0.90 to 1.10 p.u.

4.1.2 Thermal LimitsWECC member utilities follow a planning philosophy whereby normal thermal ratings shall not be violatedunder system intact conditions, and the applicable emergency rating shall not be exceeded under contingencyconditions. It should be noted that the emergency rating for all monitored PacifiCorp 230 kV transmission lines


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and transformers is 123% of the continuous thermal rating. This emergency rating is applied to all post-contingency scenarios.

4.1.3 Solution ParametersThe steady state analysis was performed with pre-contingency solution parameters that allowed adjustment ofload tap-changing (LTC) transformers, static VAR devices including switched shunt capacitors and reactors, andDC taps. Post-contingency solution parameters only allowed adjustment of DC taps. Area interchange controlwas disabled and generator VAR limits were applied immediately for all solutions. The solution methodimplemented for all cases was a fixed-slope decoupled Newton solution. To maintain consistency with the 1990TOT4A/4B study methodology, fixed capacitors in the TOT4A area were manually switched in and out ofservice as necessary to help meet the performance criteria.

Table 5: Steady State Solution Parameters

Case Area Interchange TransformerLTCsPhase

ShiftersStatic VAR

Devices DC Taps

Pre-Contingency Disabled Stepping Disabled Stepping (discrete) Enabled

Post-Contingency Disabled Disabled Disabled Disabled Enabled

4.2 Case Naming ConventionStudy case designations were formatted as shown in Figure 2:

POI_ Resource Type_ RCDC Tie Schedule_ Network Gen Offset by Wind_ Prior Outage

POI: 1 Tap bus on Pumpkin Buttes-Teckla 230 kV line2 Pumpkin Buttes 230 kV bus

Wind Resource Type: A Proposed Project Off-line

B Energy Resource (Dispatched to Currant Creek)C Network Resource

RCDC Tie Schedule: 1 200 MW E>W2 Blocked (0 MW)

Generation Offset: A No OffsetB 300 MW Network Resource ReductionC 500 MW Network Resource Reduction

Prior Outage: See Tables 6 and 7

Figure 2: Case Naming Convention


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Table 6: Pre-Wind Prior Outage List

Steady State Pre-Wind Prior Outage List1 SYSTEM INTACT 18 TECKLA-DJ MR 35 WYGEN3 UNIT

2 GOOSE CRK-SHERIDAN 19 RENO-TECKLA 36 DRYFORK UNIT

3 BUFFALO-SHERIDAN 20 DONKEY CRK-RENO 37 LRS UNIT

4 BUFFALO-KAYCEE 21 DONKEY CRK- P. BUTTES 38 DJ UNIT

5 CASPER-CLAIMJPR 22 WYODAK-DONKEY CRK 39 CASPER XFMR

6 CASPER-DJ 23 WYODAK-OSAGE 40 DJ XFMR

7 SHERIDAN-T. RIVER 24 WYODAK-HUGHES 41 WYODAK XFMR 2

8 T. RIVER-ARVADA 25 HUGHES-LOOKOUT 42 WESTHILL XFMR

9 ARVADA-DRYFORK 26 YELLOW CREEK-OSAGE 43 OSAGE XFMR

10 DRYFORK-CARR DRAW RB 27 LOOKOUT-YELLOW CREEK 44 LANGE XFMR 2

11 DRYFORK-HUGHES RB 28 OSAGE-WESTHILL 45 LOOKOUT XFMR 2

12 BUFFALO-CARR DRAW 29 LANGE-LOOKOUT 46 YELLOWCREEK XFMR

13 WYODAK-CARR DRAW 30 LANGE-SOUTH RAPID 47 SOUTH RAPID XFMR

14 CARR DRAW-BARBER CREEK 31 SOUTH RAPID-WESTHILL 48

15 BARBER CREEK- P. BUTTES 32 RCDCW-SOUTH RAPID 49

16 P. BUTTES -TECKLA 33 WESTHILL-STEGALL 50

17 P. BUTTES -DJ 34 WYODAK UNIT 51

*RB indicates Dryfork runback *MR indicates Barber Creek and Hartzog DG Must Run (Heavy Summer loads only)

Table 7: Post-Wind Prior Outage List

Steady State Post-Wind Prior Outage List1 SYSTEM INTACT 18 TECKLA-DJ MR 35 WYGEN3 UNIT

2 GOOSE CRK-SHERIDAN 19 RENO-TECKLA 36 DRYFORK UNIT3 BUFFALO-SHERIDAN 20 DONKEY CRK-RENO 37 LRS UNIT

4 BUFFALO-KAYCEE 21 P. BUTTES -DJ 38 WYODAK UNIT

5 CASPER-CLAIMJPR 22 DONKEY CRK- P. BUTTES 39 DJ UNIT

6 CASPER-DJ 23 WYODAK-DONKEY CRK 40 CASPER XFMR

7 SHERIDAN-T. RIVER 24 WYODAK-OSAGE 41 DJ XFMR

8 T. RIVER-ARVADA 25 WYODAK-HUGHES 42 WYODAK XFMR 2

9 ARVADA-DRYFORK 26 HUGHES-LOOKOUT 43 WESTHILL XFMR

10 DRYFORK-CARR DRAW RB 27 YELLOW CREEK-OSAGE 44 OSAGE XFMR

11 DRYFORK-HUGHES RB 28 LOOKOUT-YELLOW CREEK 45 LANGE XFMR 2

12 BUFFALO-CARR DRAW 29 OSAGE-WESTHILL 46 LOOKOUT XFMR 2

13 WYODAK-CARR DRAW 30 LANGE-LOOKOUT 47 YELLOWCREEK XFMR

14 CARR DRAW-BARBER CREEK 31 LANGE-SOUTH RAPID 48 SOUTH RAPID XFMR

15 BARBER CREEK- P. BUTTES 32 SOUTH RAPID-WESTHILL 49

16 P. BUTTES-PBWIND 33 RCDCW-SOUTH RAPID 50

17 PBWIND-TECKLA 34 WESTHILL-STEGALL 51

*RB indicates Dryfork runback *MR indicates Barber Creek and Hartzog DG Must Run (Heavy Summer loads only)


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4.3 Steady State Contingency ListA list of forced outages simulated for the various steady state scenarios is shown in Tables 8-9.

Table 8: Pre-Wind Scenario Contingency List

Pre-Wind Forced Outage List1 ATLANTIC-WYOPO-1 26 RIVERTON-WYOPO-1 51 TONGRIVR-DRYFORK-1

2 BADWATER-SPENCE-1 27 SHERIDAN-TONGRIVR-1 52 CARR DRA- P. BUTTES

3 BADWATER-THERMOPL-1 28 WYODAK-OSAGE-1 53 TECKLA-DJ

4 BUFFALO-CARR DRA-1 29 WYODAK-HUGHES-1 54 WYODAK UNIT

5 BUFFALO-KAYCEE-1 30 WYODAK-DONKYCRK-1 55 WYGEN3 UNIT

6 BUFFALO-SHERIDAN-1 31 YELOWTLP-YELLOWBR-1 56 DRYFORK UNIT

7 CARR DRA-WYODAK-1 32 LOVELL-THERM 115 57 LRS UNIT

8 CARR DRA-DRYFORK-1 33 BGEORGE-LOVELL-1 58 DJ3 UNIT

9 CASPERPP-DAVEJOHN-1 34 BGEORGE-THERM-1 59 CASPER XFMR

10 CASPERPP-CLAIMJPR-1 35 WESTHILL-OSAGE-1 60 DJ XFMR

11 CASPERPP-RIVERTON-1 36 WESTHILL-STEGALL-1 61 WYODAK XFMR 1

12 CASPERPP-CASPERLM-1 37 WESTHILL-RCSOUTH1-1 62 WESTHILL XFMR

13 CASPER-SPENCE-1 38 LOVELL-YELLOWBR-1 63 OSAGE XFMR

14 DAVEJOHN-DIFICULT-1 39 OSAGE-YELOWCRK-1 64 LANGE XFMR 1

15 DAVEJOHN-LAR.RIVR-1 40 LANGE-LOOKOUT1-1 65 LOOKOUT XFMR 1

16 DAVEJOHN-STEGALL-1 41 LANGE-RCSOUTH1-1 66 YELLOWCREEK XFMR

17 DAVEJOHN-P. BUTTES-1 42 RENO-TEKLA-1 67 SNOWY RANGE XFMR 1

18 FRANNIE-GARLAND-1 43 RENO-DONKYCRK-1 68 RCSOUTH XFMR 1

19 FRANNIE-YELOWTLP-1 44 LOOKOUT1-YELOWCRK-1 69 HUGHES XFMR

20 GOOSE CK-SHERIDAN-1 45 LOOKOUT1-HUGHES-1 70

21 GOOSE CK-YELOWTLP-1 46 TEKLA- P. BUTTES -1 71

22 GRASS CK-OREBASIN-1 47 WYODAK-HUGHES-69 72

23 GRASS CK-THERMOPL-1 48 HUGHES-DRYFORK-1 73

24 MUSTANG-SPENCE-1 49 RCSOUTH1-RCDC W-1 74

25 RIVERTON-THERMOPL-1 50 DONKYCRK- P. BUTTES -1 75


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Table 9: Post-Wind Scenario Contingency List

Post-Wind Forced Outages

1 ATLANTIC-WYOPO-1 26 RIVERTON-WYOPO-1 51 HUGHES-DRYFORK-1

2 BADWATER-SPENCE-1 27 SHERIDAN-TONGRIVR-1 52 RCSOUTH1-RCDC W-1

3 BADWATER-THERMOPL-1 28 WYODAK-OSAGE-1 53 DONKYCRK- P. BUTTES -14 BUFFALO-CARR DRA-1 29 WYODAK-HUGHES-1 54 TONGRIVR-DRYFORK-1

5 BUFFALO-KAYCEE-1 30 WYODAK-DONKYCRK-1 55 CARR DRA- P. BUTTES

6 BUFFALO-SHERIDAN-1 31 YELOWTLP-YELLOWBR-1 56 TECKLA-DJ

7 CARR DRA-WYODAK-1 32 LOVELL-THERM 115 57 WYODAK UNIT

8 CARR DRA-DRYFORK-1 33 BGEORGE-LOVELL-1 58 WYGEN3 UNIT

9 CASPERPP-DAVEJOHN-1 34 BGEORGE-THERM-1 59 DRYFORK UNIT

10 CASPERPP-CLAIMJPR-1 35 WESTHILL-OSAGE-1 60 LRS UNIT

11 CASPERPP-RIVERTON-1 36 WESTHILL-STEGALL-1 61 DJ3 UNIT

12 CASPERPP-CASPERLM-1 37 WESTHILL-RCSOUTH1-1 62 CASPER XFMR

13 CASPER-SPENCE-1 38 LOVELL-YELLOWBR-1 63 DJ XFMR

14 DAVEJOHN-DIFICULT-1 39 OSAGE-YELOWCRK-1 64 WYODAK XFMR 1

15 DAVEJOHN-LAR.RIVR-1 40 LANGE-LOOKOUT1-1 65 WESTHILL XFMR16 DAVEJOHN-STEGALL-1 41 LANGE-RCSOUTH1-1 66 OSAGE XFMR

17 DAVEJOHN- P. BUTTES -1 42 RENO-TEKLA-1 67 LANGE XFMR 1

18 FRANNIE-GARLAND-1 43 RENO-DONKYCRK-1 68 LOOKOUT XFMR 1

19 FRANNIE-YELOWTLP-1 44 LOOKOUT1-YELOWCRK-1 69 YELLOWCREEK XFMR

20 GOOSE CK-SHERIDAN-1 45 LOOKOUT1-HUGHES-1 70 SNOWY RANGE XFMR 1

21 GOOSE CK-YELOWTLP-1 46 TEKLA-PB WIND-1 71 RCSOUTH XFMR 1

22 GRASS CK-OREBASIN-1 47 PB WIND- P. BUTTES -1 72 HUGHES XFMR

23 GRASS CK-THERMOPL-1 48 PB WIND-PB WIND2 73

24 MUSTANG-SPENCE-1 49 HARTZOG-PB WIND2 74

25 RIVERTON-THERMOPL-1 50 WYODAK-HUGHES-69 75

4.4 Steady State Base Case Dispatch and Interface ConditionsThe steady state analysis looked at the addition of the project as an Energy Resource (ER) and a Network Resource(NR). The ER scenario was dispatched against Currant Creek generation in Utah, with no changes made togeneration on the CUS. The NR was dispatched against network generation. First, the RCDC Tie was blocked inscenarios where it was online, and on-line gas generation was taken off-line. The remainder of the proposed

projects generation was dispatched against network base load generation on a pro-rata basis.

Refer to Appendix B for a summary of generation dispatch and transmission line flows for the various system-intactscenarios described in 4.2. Summaries include Pumpkin Buttes-Teckla POI cases only.

5 Steady State Analysis ResultsSeveral criteria violations were discovered during the steady state analysis and were omitted from the results summary

below due to their numerous occurrences. In scenarios where the proposed project was interconnected to a tap bus between Pumpkin Buttes and Teckla, loss of one of the 230 kV line segments connected to the tap bus overloaded theremaining line. Utilizing this POI would require a second 230 kV circuit from the tap bus to Pumpkin Buttes. Allviolations that could be mitigated through the application of existing BHP operating procedures were also omitted.


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5.1 Light Winter Pre-Wind ResultsThere were no criteria violations during the light winter pre-wind steady state analysis.

5.2 Light Winter Energy Resource ResultsThe addition of the proposed project as an Energy Resource in the light winter case resulted in numerous prior andforced outage combinations which did not converge. The most critical prior outage was the loss of the Goose Creek-Sheridan 230 kV line. A solution could not be reached for most outage combinations that resulted in the loss of twoCUS outlet paths. The Alcova-CasperLM 115 kV line became overloaded under numerous prior and forced outagecombinations in the light winter Energy Resource scenarios.

A reduction of the proposed project to 250 MW resulted in the mitigation of all criteria violations except the Alcova-CasperLM 115 kV overload. However, the Alcova-CasperLM 115 kV line rating is currently planned to beupgraded by WAPA prior to the Interconnection Customers in-service date.

In order to interconnect the proposed project at the full 500 MW, a new transmission path would be needed to provide additional capacity for transfers out of the study area. The TOT 4B path appeared to be the limiting elementin the light winter analysis. As a sensitivity, a new 230 kV path from the new Tongue River 230 kV switchingstation to the existing Yellowtail 230 kV substation was modeled and the simulations were repeated. Even with theadditional line between Yellowtail and Tongue River, the possibility still existed for the loss of two TOT 4Belements from the CUS toward Yellowtail. A second line was added to the case, from the existing Carr Draw 230kV substation to the new Tongue River 230 kV switching station. This transmission addition was used as one

possible solution to the issue of insufficient transmission capacity for transfers outside the study area. Additionalsolutions may be identified during the System Impact Study or Transmission Service Request Study if the customerelects to proceed with the project. The optimal solution will be directly dependent on the size of the project and thespecified Point of Delivery for the resource.

The Alcova-CasperLM 115 kV line also required a thermal rating increase to at least 91 MVA to prevent anoverload. However, this line rating is currently scheduled to be increased by WAPA. The additional 230 kV pathfrom Carr Draw-Tongue River-Yellowtail and the Alcova-CasperLM 115 kV upgrade mitigated all criteriaviolations. Results were similar for either POI.

5.3 Light Winter Network Resource Results

There were no criteria violations for the light winter network resource steady state analysis due to the interconnectionof the proposed project.

5.4 Heavy Summer Pre-Wind ResultsThe steady state analysis for the 2011 heavy summer pre-wind case revealed no voltage criteria violations. Thermalcriteria violations on the Lovell-Nahne Jensen 115 kV line were experienced following the prior outage of theWyodak, Dryfork, LRS, or Dave Johnston generator and the forced outage of the PACE-WAPA 230 kV tie line atYellowtail. This overload occurred only for cases with the RCDC Tie off-line.

5.5 Heavy Summer Energy Resource ResultsThere were no voltage criteria violations as a result of the addition of the proposed project. The worst-case thermaloverload occurred on the Dave Johnston-Dave Johnston South Tap-Refinery 115 kV line following a Casper 230:115kV prior outage coupled with the forced outage of the DJ-LRS 230 kV line. The overloads were similar for either

POI scenario. A manual reduction in the output of the proposed project to 250 MW mitigated all overload violations.To accommodate the entire proposed 500 MW project, the Carr Draw-Tongue River-Yellowtail 230 kV linedescribed in 5.2 was inserted in the case to provide an additional CUS and TOT 4B transmission path. Also, theDave Johnston-Dave Johnston South Tap 115 kV line was upgraded to 185 MVA. Loading on the Dave JohnstonSouth Tap-Refinery 115 kV line was reduced to 100% of the continuous thermal rating following the addition of theCarr Draw-Tongue River-Yellowtail 230 kV line.

5.6 Heavy Summer Network Resource Results


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The heavy summer network resource analysis revealed results similar to those described in 5.4. There was a 1.6%increase in the overload for the LRS and DJ generator prior outage cases, but this difference can be considerednegligible. There were no measurable differences in the results between either POI.

6 Stability Analysis Methodology

6.1 Stability Analysis MethodologyThe primary objective of the stability analysis is to analyze the impact of the project on transient stability performanceof the bulk electric system for various system disturbances. Stability simulations were conducted with and without the

proposed interconnection project for the 2011 light winter load level scenario to confirm performance with respect toapplicable criteria.

6.1.1 Stability Performance CriteriaThe disturbance performance criteria for this study requires that the transient low voltage swing shall not belower than 0.70 p.u. at any load or non-load bus and the system shall exhibit positive damping following anycontingency. Table W-1 of the NERC/WECC Planning Standards states that for a NERC Category Bcontingency, the frequency at a load bus must not dip below 59.6 HZ for more than 6 cycles, but thisrequirement was applied to all contingencies to simplify the presentation of the results.

6.1.2 Low Voltage Ride Through CriteriaThe current WECC Low Voltage Ride Through (LVRT) Standard requires generators to remain in-service for 3-

phase faults with normal clearing (4-9 cycles) and single line-to-ground faults with delayed clearing that resultin a GSU high side voltage of 0.15 per unit or greater. The FERC LVRT Standard, however, requires generationto remain on-line for GSU high side voltages of 0 per unit for similar faults. The more stringent FERC standardwas applied as the LVRT requirement for this study.

6.2 Stability Base Case Dispatch and Interface ConditionsThe stability base case dispatch and interface conditions were a subset of the steady state base case dispatch andinterface conditions listed in Section 4.2. Dynamic simulations were run for the following light winter scenarios:

1B1A1 1C1B1 1C1C1 1C2B1

2B1A1 2C1B1 2C1C1 2C2B1

6.3 Stability Fault DescriptionsIn addition to a disturbance-free steady state simulation, each dispatch scenario for the 2011 light winter load casewas simulated with various faults applied. Table 10 lists the faults and the load cases in which they were applied.

Table 10: Stability Fault Descriptions

Fault Description Simulated Cases3 PH Bus Fault Cleared Element

FaultDuration POI Resource

Wyodak 230 Wyodak-Carr Draw 230 line 4.25 cycles Both ER, NRWyodak 230 Wyodak-Donkey Crk 230 line 4.25 cycles Both ER, NR

Donkey Crk 230 Donkey Creek-Reno 230 line 4.25 cycles Both ER, NRP. Buttes 230 kV P. Buttes-Carr Draw 230 line 4.25 cycles Both ER, NRDonkey Crk 230 P. Buttes-Donkey Crk 230 line 4.25 cycles Both ER, NR

PBWind 230 P. Buttes-PBWind 230 line 4.25 cycles PB-Teckla ER, NRPBWind 230 P. Buttes-Teckla 230 line 4.25 cycles PB-Teckla ER, NRP. Buttes 230 P. Buttes-Teckla 230 line 4.25 cycles P. Buttes ER, NR

PBWind2 230 * N/A 9 cycles P. Buttes ER* This fault was used to test the LVRT performance of the proposed wind farm


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7 Stability Analysis Results

There were no stability performance criteria violations observed on the transmission system as a result of theinterconnection of the proposed project. All post-contingent voltage dips remained well above the established limit androtor angles were positively damped. Additionally, there were no frequency excursions below the 59.6 HZ limit.

8 TOT 4A/4B Analysis

8.1 TOT 4A/4B Analysis ProcedureTOT 4A and TOT4B are transmission paths in Wyoming that may be affected by additions or changes to thetransmission system. TOT4A is an interface that is used to measure power flows from the study area to thesouthwest, and TOT4B is used to measure flows to the northwest. The ratings of the path are interdependent, and aredefined using a nomogram defined in the WECC 2008 Path Rating Catalog. Transmission lines included in TOT4Aare:

Riverton-Wyopo 230 kV Dave Johnston-Difficulty 230 kV Spence-Mustang 230 kV

and transmission lines included in TOT4B for this study are:

Carr Draw-Buffalo 230 kV Casper-Claim Jumper 230 kV Riverton-Thermopolis 230 kV Riverton 230/115 kV transformers Alcova-Raderville 115 kV Spence-Thermopolis 230 kV Tongue River-Sheridan 230 kV

Adjustments were made to the system to reach the various operating points on the nomogram. These adjustmentsincluded generation dispatch on either side of the path interfaces, changes to the phase shifter angles at Monumentand the Yellowtail area, and DC tie schedules at Rapid City, Stegall, and Sidney. The Miles City DC tie was blockedfor this analysis and the Foote Creek wind farm was online at 135 MW. The forced outages in Table 11 weresimulated at each of the operating points on the nomogram. The operating criteria listed in 4.1 were applied duringthis analysis.


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Table 11: TOT 4A/4B Study Contingency List

TOT 4A/4B STUDY FORCED OUTAGES1 BRDGR 345-230 XFMR 46 YELLOWBR XFMR 91 GRASSCRK-THERMOPL

2 BAR-X XFMR 47 HUGHES XFMR 92 KAYCEE-MIDWEST

3 BRDGR 230-34.5 XFMR 48 BLGS PHA-YELOWTLP 93 MINERS-PLATTE; FT CRK RAS

4 CASPER XFMR 49 CROS PHA-YELLOWBR 94 MUSTANG-SPENCE

5 DJ XFMR 50 RIMROCK P. SHIFTER 95 PALISADE-RAVEN

6 DJ3 GSU 51 ATLANTIC-ROCKSPR 96 PALISADE-ROCKSPGS

7 DJ4 GSU 52 ATLANTIC-WYOPO 97 LOVELL-YELLOWBR

8 FLAMING GORGE XFMR 1 53 BADWATER-SPENCE 98 RIVERTON-THERMOPL

9 FLAMING GORGE XFMR 2 54 BADWATER-THERMOPL 99 LOVELL-THERMOPL 115

10 FRANNIE XFMR 1 55 BLUERIM-BRIDGER PP 100 BGEORGE-LOVELL

11 FT CRK-FT CRK2 XFMR 56 BLUERIM-S TRONA 101 BGEORGE-THERMOPL

12 FT CRK-FT CRK 1 XFMR 57 BRIDGERPP-FIREHOLE 102 RIVERTON-WYOPO

13 GARLAND XFMR 58 BRIDGER-MUSTANG 103 WYODAK-OSAGE

14 GRASS CRK XFMR 59 BRIDGER-ROCKSPGS 104 WYODAK-DONKEYCRK

15MIDWEST XFMR 1

60BUFFALO-CARRDRAW

105DONKEYCRK-RENO

16 MINERS XFMR 61 BUFFALO-KAYCEE 106 DONKEYCRK-HARTZOG

17 MUSTANG XFMR 62 BUFFALO-SHERIDAN 107 WYODAK-HUGHES

18 OREBASIN-OB 34.5 XFMR 63 CARR DRAW-WYODAK 108 YELLOWTLP-YELLOWBR

19 OREBASIN-OB 69 XFMR 64 CARR DRAW-DRYFORK 109 ARCHER-AULT

20 PLATTE XFMR 65 CARR DRAW-HARTZOG 110 ARCHER-STEGALL

21 PT ROCKS XFMR 66 TONGUE RIVR-DRYFORK 111 ARCHER-HAYDEN

22 RIVERTON XFMR 67 HUGHES-DRYFORK 112 AULT-LARAMIE RIVR

23 ROCKSPRINGS XFMR 68 CASPERPP-DJ 113 WESTHILL-OSAGE

24 SHERIDAN XFMR 69 CASPERPP-CLAIMJPR 114 WESTHILL-STEGALL

25 THERMOPL-THERPACE XFMR2 70 CASPERPP-RIVERTON 115 WESTHILL-RCSOUTH

26 WYODAK GSU 71 CASPERPP-CASPERLM 116 LAR. RIVR-STEGALL

27 WYODAK XFMR2 72 CASPER-SPENCE 117 LAR. RIVR-STORY28 WYGEN GSU 73 DJ-DIFICULT; FTCRK RAS 118 N. YUMA-SIDNEY

29 WYGEN2 GSU 74 TECKLA-DJ 119 OSAGE-YELLOWCRK

30 WYOPO XFMR 75 DJ-LAR RIVR 120 LANGE-LOOKOUT

31 YELOWTLP XFMR 76 DJ-STEGALL 121 LANGE-RCSOUTH

32 ARCHER XFMR 77 DECKER-TONGUE RIVR 122 RENO-TECKLA

33 WESTHILL XFMR 78 SHERIDAN-TONGUE RIVR 123 SIDNEY-STEGALL

34 LRS XFMR 79 DECKER-WYOMONT 124 LOOKOUT-YELLOWCRK

35 MBPP1 GSU 80 MINERS-DIFFICULTY 125 LOOKOUT-HUGHES

36 OSAGE XFMR 81 FIREHOLE-LITTLEMT 126 STEGALLDC-STEGALL

37 LANGE XFMR 82 FIREHOLE-ROCKSPGS 127 TECKLA-PBWIND

38 SIDNEY XFMR 83 FLAMINGGORG-LITTLEMT 128 PBWIND-HARTZOG

39 SIDNEY-SIDNEYDC 84 FRANNIE-GARLAND 129 PBWIND-PBWIND240 SNOWYRNG XFMR 1 85 FRANNIE-YELOWTLP 130 RCSOUTH-RCDCW

41 MIRACLEM XFMR 1 86 FT. CRK-MINERS 131 HARTZOG-DJ

42 LOOKOUT XFMR 1 87 GARLAND-OREBASIN 132 R.SPRG-PT.RCKS-BRDGR

43 YELLOWCRK XFMR 1 88 GOOSECRK-SHERIDAN 133 PT.RCKS-BARX-PLATTE

44 STEGALL XFMR 2 89 GOOSECRK-YELOWTLP 134 DRYFORK UNIT

45 YELLO 3-4 GSU 90 GRASSCRK-OREBASIN 135


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8.2 TOT 4A/4B Analysis ResultsThe established nomogram was verified at four points using a 2011 LW pre-wind base case. Then the proposed

project was placed in-service and the study process was repeated. The nomogram was verified using four operating points similar to those used in the pre-wind analysis. The study results revealed that there were no negative impactsto the existing established TOT 4A/4B path ratings. Figure 3 summarizes the results of the analysis.

Pumpkin Buttes Wind Feasibility StudyTOT4A / TOT4B Nomog ram

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900

TOT 4A FLOW (MW)

T O T 4 B F L O W

( M W )

Existing NomogramPre-Wind NomogramPost-Wind Nomogram

Figure 3: TOT 4A/4B Analysis Results

9 Short Circuit Analysis

9.1 Short Circuit Study ModelingThe proposed generation as modeled will be connected to the 230 kV transmission system via 34.5 kV collectorsystem and four 125 MVA, 34.5/230 kV step-up transformers. Each step-up transformer has an impedance of 12%on a 29 MVA base. The step-up transformer impedance modeled in the short circuit analysis was:

Z (collector step-up) = 0.00 + J0.12 p.u. (100 MVA base)

Each lumped wind turbine generator will have a 575V/34.5kV GSU transformer rated at 30 MVA. Thesetransformers have an impedance of 20% on a 100 MVA base. The generator step-up transformer impedancemodeled in the short circuit analysis was:

Z (eq. gen step-up) = 0.00 + J0.20 p.u. (100 MVA base)


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Transformer resistance was assumed to be negligible when compared to the reactance and was set to zero for thisanalysis. The lumped generators have the following reactance values on the generator MVA base:

Xd

= Direct Axis Synchronous Reactance = 0.8 per unit

Xd

= Direct Axis Transient Reactance = 0.8 per unit

Xd

= Direct Axis Sub-transient Reactance = 0.8 per unit

These equivalent lumped generator impedance values were obtained using the PSS/E Wind program. The 34.5 kVcollector system impedances were modeled as shown in the Conceptual Project Drawing in Appendix B.

Maximum fault currents were then determined at local substations of interest or importance. These buses included:

Carr Draw 230 kV Pumpkin Buttes 230 kV Teckla 230 kV Reno 230 kV Laramie River Station 230 kV Stegall 230 kV Casper 230 kV Difficulty 230 kV Dave Johnston 230 kV

The resulting fault current was then compared to the circuit breaker interruption ratings of the breakers at the abovementioned substations.

9.2 Short Circuit Analysis ResultsThe short circuit analysis was initially performed without the proposed interconnection project. This gave the basecase fault duties of the interrupting devices. Then the proposed project was put in service at both of the proposed

points of interconnection and the short circuit study was repeated. The incremental fault duty difference between the

two studies gave the impact of the new generators on the existing interrupting devices in the study area. The shortcircuit fault currents for simulated faults at all of the moderately impacted substations are shown in Tables 12-13 .


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Table 12: Pumpkin Buttes-Teckla POI Fault Results

230 kV BusFault Fault Current W/O Project (A) Fault Current W/ Project (A) Project Contribution (A)

3L-G 2L-G 1L-G L-L 3L-G 2L-G 1L-G L-L 3L-G 2L-G 1L-G L-L

Ant. Mine 5746 5535 4835 4970 6079 5875 5134 5259 333 340 299 289

Barber Crk 7014 6759 5841 6062 7354 7103 6146 6357 340 344 305 295

Carr Draw 9334 9144 8217 8062 9673 9466 8461 8357 339 322 244 295

Casper 10261 10050 9309 8868 10335 10114 9353 8932 74 64 44 64

D. Johnston 17209 18053 18621 14877 17473 18301 18854 15107 264 248 233 230

Difficulty 4319 4087 3428 3734 4331 4097 3434 3744 12 10 6 10

Donkey Crk 13960 15243 15802 12007 14474 15738 16289 12452 514 495 487 445

LRS 12710 13269 13648 10998 12718 13276 13654 11004 8 7 6 6

P. Buttes 7595 7311 6310 6563 8711 8849 8515 7530 1116 1538 2205 967

Reno 5913 5737 5154 5110 6179 5995 5355 5341 266 258 201 231

Stegall 7589 7595 7484 6533 7597 7601 7489 6540 8 6 5 7

Teckla 6403 6314 5923 5536 6905 6881 6517 5972 502 567 594 436

Wyodak 13966 15254 15816 12012 14480 15750 16303 12457 514 496 487 445

Yellowcake 7056 6668 5311 6106 7189 6791 5385 6221 133 123 74 115

Table 13: Pumpkin Buttes POI Fault Results

230 kV BusFault Fault Current W/O Project (A) Fault Current W/ Project (A) Project Contribution (A)

3L-G 2L-G 1L-G L-L 3L-G 2L-G 1L-G L-L 3L-G 2L-G 1L-G L-L

Ant. Mine 5746 5535 4835 4970 5998 5785 5039 5189 252 250 204 219Barber Crk 7014 6759 5841 6062 7402 7169 6245 6399 388 410 404 337

Carr Draw 9334 9144 8217 8062 9707 9509 8511 8387 373 365 294 325

Casper 10261 10050 9309 8868 10336 10115 9354 8933 75 65 45 65

D. Johnston 17209 18053 18621 14877 17469 18301 18856 15103 260 248 235 226

Difficulty 4319 4087 3428 3734 4331 4097 3434 3744 12 10 6 10

Donkey Crk 13960 15243 15802 12007 14485 15758 16309 12462 525 515 507 455

LRS 12710 13269 13648 10998 12718 13276 13654 11004 8 7 6 6

P. Buttes 7595 7311 6310 6563 8937 9602 9931 7726 1342 2291 3621 1163

Reno 5913 5737 5154 5110 6128 5941 5306 5298 215 204 152 188

Stegall 7589 7595 7484 6533 7598 7602 7489 6541 9 7 5 8

Teckla 6403 6314 5923 5536 6776 6715 6314 5860 373 401 391 324

Wyodak 13966 15254 15816 12012 14491 15770 16324 12467 525 516 508 455

Yellowcake 7056 6668 5311 6106 7169 6772 5371 6204 113 104 60 98

It should be noted that the values in Tables 12-13 represent the largest bus phase current for the listed fault. Detailedfault analysis results will be provided upon request .


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delivery point outside the study area. A new 150-mile 230 kV TOT4B path was modeled in the study to accommodatethe additional generation without criteria violations. Costs of the new path as modeled were estimated at $44,200,000.The thermal capacity on the Alcova-CasperLM 115 kV line would need to be increased to at least 109 MVA. Theupgrade would require a CT tap ratio increase at the Casper terminal, which is currently planned as part of WAPAsMiracle Mile transmission project. A thermal capacity increase on the Dave Johnston-Dave Johnston South Tap 115kV line was also required. Costs of rebuilding the line were estimated at $280,000. Reducing the size of the project to250 MW required only the Alcova-CasperLM upgrade.

No necessary upgrades to the existing transmission system were identified for a Network Resource interconnection.

All cost estimates include labor and materials for network infrastructure only, and do not reflect any additionalancillary services that may be necessary. All direct assigned costs associated with radial transmission and/orequipment from the point of interconnection (POI) to the generation facility would be the sole responsibility of thecustomer. Preliminary cost estimates are subject to change pending a review of detailed design information of the

projects collector system in the Facility Study, providing the customer elects to proceed with the project.

Interconnection Service in and of itself does not convey any right to deliver electricity to any specific customer or Pointof Delivery. Curtailment of the proposed interconnection project may be necessary under certain emergency operatingconditions..


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APPENDIX A

PRELIMINARY ONE-LINE DIAGRAMSOF

PROPOSEDWIND FARM


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PSS/E SINGLE-LINE REPRESENTATION

BHBE-G7 Feasibility Study 040108

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