GENERATOR INTERCONNECTION REQUEST
BHBE-G7
Interconnection System Impact Study
PREPARED
BY
BLACK HILLS CORPORATION
TRANSMISSION PLANNING
August 21, 2008
Executive Summary
Black Hills Power conducted an Interconnection System Impact Study (SIS) under the guidance of the Common Use
System (CUS) Joint Open Access Transmission Tariff Large Generator Interconnection Procedures (LGIP) for the
interconnection customer to construct and interconnect a 200 MW wind farm in northeast Wyoming. The proposed
project consists of one hundred thirty-four (134) 1.5 MW GE wind turbine generators and will connect to the CUS 230
kV transmission system at the Pumpkin Buttes substation in Campbell County, Wyoming. The initial interconnection
date for the project is September 2010.
The SIS was performed based upon the information set forth in the signed LGIP Interconnection System Impact Study
agreement dated April 30, 2008.
The purpose of the study was to:
(i)
Analyze the steady-state and short circuit conditions for the project
(ii) Evaluate transient 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 of
the transmission system.
The primary area of concern for this study is northeast Wyoming. The proposed project is to be interconnected at the
existing Pumpkin Buttes 230 kV substation. The project was evaluated as both an Energy Resource and as a Network
Resource.
Steady-State Analysis
Steady-state voltage and thermal analysis examined system performance without the proposed project in order to
establish a baseline for comparison. System performance was re-evaluated with the project in place and compared with
the baseline performance to demonstrate the impact of the project on local transmission reliability. The analysis
determined that no steady-state criteria were violated as a result of the interconnection.
Stability Analysis
Stability analysis evaluated the impact of the proposed project on transmission system performance for the light winter
load level, as high energy exports and lower load levels present a worst-case model. Several wind dispatch scenarios
were utilized during the stability analysis.
The stability analysis identified the project’s impacts on the transmission system following several different
disturbances and verified the project’s Low Voltage Ride-Through (LVRT) capability was in accordance with current
FERC LVRT requirements. Stability analysis results showed that no transient stability criteria were violated as a result
of the proposed interconnection.
TOT 4A/4B Analysis
The results of the TOT 4A/4B analysis performed in the Feasibility Study (FS) verified that there were no negative
impacts to TOT4A and TOT4B as a result of interconnecting the proposed wind plant. A 300 MW reduction of the
original project size as studied in the FS was not expected to increase negative impacts to the TOT 4A/4B paths;
therefore the TOT analysis was not repeated for this study.
Short Circuit Analysis
Short circuit analysis was performed during the FS to assess the impact of the proposed project on the fault current
levels and breaker duty in the area. The surrounding breakers were evaluated to determine if the additions to the
transmission system created any breaker over-duty conditions. No adverse short circuit impacts were identified as a
result of interconnecting the original 500 MW proposed project. The short circuit analysis was not repeated for the
SIS.
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
2
Conclusion
The interconnection System Impact Study identified no necessary upgrades to the local transmission system to
accommodate the full 200 MW injection from the proposed wind project.
Network facilities required to interconnect the project are a new 230 kV bay in the Pumpkin Buttes substation with an
estimated cost of $2,000,000.
Additional reactive equipment will be required to mitigate the charging effects of the wind park collector system,
particularly under light load conditions with no wind generation output.
Interconnection Service in and of itself does not convey any right to deliver electricity to any specific customer or Point
of Delivery. Curtailment of the proposed interconnection project may be necessary under certain emergency operating
conditions.
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
3
Table of Contents
Background ............................................................................................................................... 6
1.1
Study Objective................................................................................................................... 6
1.2
Project Description ............................................................................................................. 6
1.3
Modeled Layout.................................................................................................................. 7
2
Study Area ................................................................................................................................. 8
2.1
Transmission System .......................................................................................................... 8
3
Base Case Development............................................................................................................ 8
3.1
Base Case Origin and Year................................................................................................. 8
3.2
Area Load ........................................................................................................................... 8
3.3
Planned Projects.................................................................................................................. 8
3.4
Analytical Tools.................................................................................................................. 9
4
Steady State Analysis Methodology ........................................................................................ 9
4.1
Steady State Analysis Methodology ................................................................................... 9
4.1.1
Voltage Limits ............................................................................................................ 9
4.1.2
Thermal Limits ......................................................................................................... 10
4.1.3
Solution Parameters .................................................................................................. 10
4.2
Case Naming Convention ................................................................................................. 10
4.3
Steady State Contingency List.......................................................................................... 11
4.4
Steady State Base Case Dispatch and Interface Conditions ............................................. 12
5
Steady State Analysis Results ................................................................................................ 12
5.1
Light Winter Pre-Wind Results ........................................................................................ 12
5.2
Light Winter Energy Resource Results ............................................................................ 12
5.3
Light Winter Network Resource Results .......................................................................... 12
5.4
Heavy Summer Pre-Wind Results .................................................................................... 12
5.5
Heavy Summer Energy Resource Results ........................................................................ 12
5.6
Heavy Summer Network Resource Results...................................................................... 12
6
Stability Analysis Methodology ............................................................................................. 12
6.1
Stability Analysis Methodology ....................................................................................... 13
6.1.1
Stability Performance Criteria .................................................................................. 13
6.1.2
Low Voltage Ride Through Criteria......................................................................... 13
6.2
Stability Base Case Dispatch and Interface Conditions.................................................... 13
6.3
Stability Fault Descriptions .............................................................................................. 13
7
Stability Analysis Results ....................................................................................................... 14
8
TOT 4A/4B Analysis............................................................................................................... 14
9
Short Circuit Analysis ............................................................................................................ 14
10 Conclusions.............................................................................................................................. 15
1
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
4
Appendices
APPENDIX A: Preliminary One Line Diagrams of Proposed Wind Farm...................................... 16
List of Tables
Table 1: Proposed Project Generator Modeling Data......................................................................... 6
Table 2: Proposed Project Conductor Data......................................................................................... 6
Table 3: Proposed Project Equivalent Modeling Data........................................................................ 7
Table 4: Steady State Voltage Criteria ............................................................................................... 9
Table 5: Steady State Solution Parameters ....................................................................................... 10
Table 6: Prior Outage List ............................................................................................................... 11
Table 7: Contingency List................................................................................................................. 11
Table 8: Stability Analysis Scenarios ............................................................................................... 13
Table 9: Stability Analysis Prior Outages......................................................................................... 13
Table 10: Stability Analysis Fault Descriptions ............................................................................... 14
Table 11: Pumpkin Buttes 230 kV Interconnection Costs................................................................ 15
List of Figures
Figure 1: Modeled Layout of Proposed Project.................................................................................. 7
Figure 2: Case Naming Convention.................................................................................................. 10
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
5
1
Background
1.1 Study Objective
The primary objective of the study was to determine whether the proposed interconnection had any adverse impacts
on the reliability, stability or operating characteristics of the Bulk Electric System (BES). Comprehensive steadystate and “worst-case” stability performance was evaluated.
1.2 Project Description
The proposed project consists of one hundred thirty-four (134) 1.5 MW GE wind turbine generators, producing up to
200 MW total. The project was studied as both a network resource and an energy resource, interconnected directly
to the Pumpkin Buttes 230 kV substation.
The Project as modeled consists of the following electrical components and construction activities:
• Add a bay and necessary switchgear to the Pumpkin Buttes 230 kV substation.
• Install two 230/34.5 kV transformers that will connect the 34.5 kV collector system feeders directly to a 230
kV bus, which will be located at the project’s substation.
• Construct 134 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).
• Construct two collector buses operating at 34.5 kV nominal; each bus consisting of approximately 67 GE 1.5
MW wind turbines. The collector buses will tie into one 34.5 kV main collector bus in the project’s 230 kV:
34.5 kV substation.
1.2.1
Technical Specifications
Tables 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 Range
Type
Individual Unit
MVA Rating
MW
Lagging
Leading
Doubly-Fed Induction Generator (DFIG)
1.67
1.5
0.90
0.95
Table 2: Proposed Project Conductor Data
Proposed Project Transmission Line Data
Description
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
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
6
Table 3: Proposed Project Equivalent Modeling Data
STEP-UP
EQUIVALENT GEN
PARAMETERS
FEEDER PARAMETERS
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
16
26.7
24.0
7.8
-11.7
3
2.5
0.060
0.067
0.011
17
28.4
25.5
8.3
-12.4
4
2.0
0.048
0.053
-12.4
230/34.5 kV Xfmr
0.009
Transformer
Total
17
28.4
25.5
8.3
67
111.9
100.5
32.7
-48.9
#2 - rated 75/100/125 MVA
6
4.5
0.090
0.100
0.017
17
28.4
25.5
8.3
-12.4
(x=0.1200 on 100 MVA Base)
7
3.8
0.132
0.146
0.024
17
28.4
25.5
8.3
-12.4
8
5.5
0.163
0.181
0.030
17
28.4
25.5
8.3
-12.4
9
6.8
0.192
0.213
-11.7
0.035
Transformer
Total
16
26.7
24.0
7.8
67
111.9
100.5
32.7
-48.9
Project Total
134
223.8
101.0
65.4
-97.8
1.3 Modeled Layout
The project was modeled using lumped equivalent machines as shown in Figure 1. The POI in Figure 1 is the
Hartzog 230 kV substation. The Hartzog 230 kV bus as shown in Figure 1 is synonymous with the Pumpkin Buttes
230 kV bus. A detailed one-line diagram is included in Appendix A.
Figure 1: Modeled Layout of Proposed Project
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
7
2
Study Area
2.1 Transmission System
The 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 Station
and Stegall to the southeast, and Rapid City to the east.
3
Base Case Development
3.1 Base Case Origin and Year
The base cases originated from the Western Electricity Coordinating Council (WECC) Library as part of the 2007
Study Program. The base case for the 2011 heavy summer load scenario was the 11HS1B1P study case. The 2011
light load scenario started with the 2011LSP1SA1P study case. These base cases were selected primarily due to their
recent approval dates with the assumption that the level of accuracy regarding system representation would be higher
than that of an older base case. The seasonal cases used in the SIS were modified versions of the cases used for the
FS.
3.2
Area Load
3.2.1
2011 Heavy Summer
The 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 northeast
Wyoming area.
3.2.2
2011 Light Winter
The 2010 light winter load case was created by scaling BHP and CLF&P loads to 55% of 2011 peak summer
forecast 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 were
included.
3.3 Planned Projects
Several 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 Project
The Hughes Transmission Project was included in all study cases. The project consists of two phases, the first
of which is a new 230 kV transmission line extending from the existing Hughes 230 kV substation to the new
Dry Fork 230 kV substation and on to the existing Carr Draw 230 kV substation. The second phase consists of a
new 230 kV transmission line from the new Dry Fork 230 kV substation extending north and west to the new
Tongue River 230 kV switching station and on to the existing PacifiCorp Sheridan 230 kV substation.
3.3.2
Wyodak-Dave Johnston Area 230 kV Line
The project consists of two new 230 kV transmission lines. The first line terminates at the new Donkey Creek
substation and the Pumpkin Buttes substation. The second line terminates at the Pumpkin Buttes substation and a
yet 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 Support
Two 16 MVAR dynamic reactive devices were modeled at Teckla 230 kV substation, one device on each
tertiary winding of the existing 230/69 kV transformers. The existing 15 MVAR capacitors were modeled at
their respective 69 kV bus.
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
8
3.3.4
Rapid City Dynamic Voltage Support
A +100/-50 MVAR Static VAR Compensator was modeled on the Lange 230 kV bus.
3.3.5
Casper-Dave Johnston Transmission Project
The DJ-Spence 230 kV line was looped into the Casper 230 kV substation. The resulting parallel DJ-Casper 230
kV lines were re-conductored to maintain TOT 4A/4B nomogram capabilities.
3.3.6
Dave Johnston Wind
Two identical 99 MW wind generating projects were modeled at the Dave Johnston 230 kV bus per PaciCorp’s
request.
3.3.7
300 MW Path ‘C’ Upgrade
Various upgrades were made to the 138 kV lines between Populus and Terminal substations to increase the
transfer capability from Wyoming/Idaho to Utah by up to 300 MW.
3.3.8
Threemile Knoll 345 kV Project
The Bridger-Goshen 345 kV line was looped into a new Threemile Knoll 345/138 kV substation. Project
includes various 115 kV line additions.
Should any one of the projects listed above not be complete prior to the proposed project in-service date, the
Interconnection project may be curtailed due to transmission prior outages or other emergency conditions. These
curtailments and/or operating restrictions, if needed, will be developed and identified through operational studies as
required.
3.4 Analytical Tools
Power flow and dynamic analyses were performed using PSS/E load flow and dynamic simulation software, version
30.3.1.
4
Steady State Analysis Methodology
4.1 Steady State Analysis Methodology
The proposed project was evaluated at 2011 peak summer and light winter load levels to determine if it caused any
significant 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 reevaluated with the proposed project in-service and compared to the baseline performance to determine the impact of
the project on area transmission reliability. The criteria described below are consistent with the WECC Minimum
Operating Reliability Criteria and Colorado Coordinated Planning Group’s Voltage Coordination Guide.
4.1.1
Voltage Limits
Table 4 identifies the voltage criteria used in or around the primary study area for the steady state voltage
assessment. Pre-existing voltage violations outside the localized study area were ignored during the evaluation
of the proposed project’s impacts.
Table 4: Steady State Voltage Criteria
Applicable
Control Area
Voltage
Class
PACE, WAPA-RMR
69 kV and above
Acceptable Voltage Range
Pre-Contingency
Post-Contingency
(normal conditions)
(emergency conditions)
0.95 to 1.05 p.u.
0.90 to 1.10 p.u.
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
9
4.1.2
Thermal Limits
WECC member utilities follow a planning philosophy whereby normal thermal ratings shall not be violated
under system intact conditions, and the applicable emergency rating shall not be exceeded under contingency
conditions. It should be noted that the emergency rating for all monitored PacifiCorp 230 kV transmission lines
and transformers is 123% of the continuous thermal rating. This emergency rating is applied to all postcontingency scenarios.
4.1.3
Solution Parameters
The steady state analysis was performed with pre-contingency solution parameters that allowed adjustment of
load tap-changing (LTC) transformers, static VAR devices including switched shunt capacitors and reactors, and
DC taps. Post-contingency solution parameters only allowed adjustment of DC taps. Area interchange control
was disabled and generator VAR limits were applied immediately for all solutions. The solution method
implemented for all cases was a fixed-slope decoupled Newton solution. To maintain consistency with the 1990
TOT4A/4B study methodology, fixed capacitors in the TOT4A area were manually switched in and out of
service as necessary to help meet the performance criteria.
Table 5: Steady State Solution Parameters
Case
Area
Interchange
Transformer
LTCs
Phase
Shifters
Static VAR
Devices
DC
Taps
Pre-Contingency
Disabled
Stepping
Disabled
Stepping (discrete)
Enabled
Post-Contingency
Disabled
Disabled
Disabled
Disabled
Enabled
4.2 Case Naming Convention
Study case designations were formatted as shown in Figure 2:
Resource Type_ RCDC Tie Schedule_ Network Gen Offset by Wind_ Prior Outage
Wind Resource Type:
A
B
Energy Resource (Dispatched to Currant Creek)
Network Resource
RCDC Tie Schedule:
1
2
200 MW EÆW
Blocked (0 MW)
Generation Offset:
A
B
No Offset
200 MW Network Resource Reduction
Prior Outage:
See Table 6
Figure 2: Case Naming Convention
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
10
Table 6: Prior Outage List
Steady State Pre-Wind Prior Outage List
1
SYSTEM INTACT
18
P. BUTTES -DJ
35
WYODAK UNIT
2
GOOSE CRK-SHERIDAN
19
TECKLA-ANTELOPE MR
36
WYGEN3 UNIT
3
BUFFALO-SHERIDAN
20
RENO-TECKLA
37
DRYFORK UNIT
4
BUFFALO-KAYCEE
21
DONKEY CRK-RENO
38
LRS 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
P. BUTTES -TECKLA
*RB indicates Dryfork runback
WESTHILL-STEGALL
34
51
*MR indicates Barber Creek and Hartzog DG Must Run (Heavy Summer loads only)
4.3 Steady State Contingency List
A list of forced outages simulated for the various steady state scenarios is shown in Table 7.
Table 7: Contingency List
Pre-Wind Forced Outage List
1
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
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
11
4.4 Steady State Base Case Dispatch and Interface Conditions
The 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 to generation on the CUS. The NR scenarios dispatched the proposed project against network
generation. First, the RCDC Tie was blocked in scenarios where it was on-line, and on-line gas generation
was taken off-line. The remainder of the proposed project’s 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 systemintact scenarios described in 4.2.
5
Steady State Analysis Results
All violations that could be mitigated through the application of existing BHP operating procedures were
omitted. Also, high voltage violations due to improperly configured capacitors were not included in the results.
5.1 Light Winter Pre-Wind Results
There were no criteria violations during the light winter pre-wind steady state analysis.
5.2 Light Winter Energy Resource Results
The Alcova-CasperLM 115 kV line became overloaded for several prior and forced outage combinations in
the light winter Energy Resource scenarios. However, the Alcova-CasperLM 115 kV line rating is currently
planned to be upgraded by WAPA prior to the Interconnection Customers in-service date.
5.3 Light Winter Network Resource Results
There were no criteria violations for the light winter network resource steady state analysis due to the
interconnection of the proposed project.
5.4 Heavy Summer Pre-Wind Results
The steady state analysis for the 2011 heavy summer pre-wind case revealed no voltage criteria violations.
Thermal criteria violations on the Lovell-Nahne Jensen 115 kV line were experienced following the prior
outage of a Wyodak, Dryfork, LRS, or Dave Johnston generator and the forced outage of the PACE-WAPA
230 kV tie line at Yellowtail. This overload occurred only for cases with the RCDC Tie off-line.
5.5 Heavy Summer Energy Resource Results
There were no voltage criteria violations as a result of the addition of the proposed project.
5.6 Heavy Summer Network Resource Results
The heavy summer network resource analysis revealed results similar to those described in 5.4. There was a
0.5% increase in the overload for the LRS generator prior outage case, but this difference was considered
negligible.
A sensitivity analysis was performed on the light winter study case with the proposed wind plant off-line in
order to observe the charging effect of the proposed interconnection’s collector system. The collector system as
modeled supplied approximately 15 MVARs at the POI. The model as depicted in Appendix A contained a
slightly different collector system layout than the model used for this study. This alternate representation was
found to supply approximately 20 MVARs at the POI. The risk of an over-voltage condition may arise when the
local transmission system is lightly loaded and the wind turbines are not generating.
6
Stability Analysis Methodology
____________________________________________________________________________________________________________
BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
12
6.1 Stability Analysis Methodology
The primary objective of the stability analysis is to analyze the impact of the project on transient stability
performance of 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 to applicable criteria.
6.1.1
Stability Performance Criteria
The disturbance performance criteria for this study requires that the transient low voltage swing shall not
be lower than 0.70 p.u. at any load or non-load bus and the system shall exhibit positive damping
following any contingency. Table W-1 of the NERC/WECC Planning Standards states that for a NERC
Category B contingency, the frequency at a load bus must not dip below 59.6 HZ for more than 6 cycles,
but this requirement was applied to all contingencies to simplify the presentation of the results.
6.1.2
Low Voltage Ride Through Criteria
The current WECC Low Voltage Ride Through (LVRT) Standard requires generators to remain inservice for 3-phase faults with normal clearing (4-9 cycles) and single line-to-ground faults with delayed
clearing that result in a GSU high side voltage of 0.15 per unit or greater. The FERC LVRT Standard,
however, requires generation to remain on-line for GSU high side voltages of 0 per unit for similar faults.
The more stringent FERC standard was applied as the LVRT requirement for this study.
6.2 Stability Base Case Dispatch and Interface Conditions
The stability base case dispatch and interface conditions were a subset of the steady state base case conditions
listed in Section 4.2. Dynamic simulations were run for the following light winter load scenarios:
Table 8: Stability Analysis Scenarios
Scenario Name
A1AX
A2AX
B2AX
B2BX
Scenario Description
Energy Resource, RCDC @ 200MW EÆW, No Network Generation Offset
Energy Resource, RCDC Blocked, No Network Generation Offset
Network Resource, RCDC Blocked, No Network Generation Offset
Network Resource, RCDC Blocked, 200 MW Network Generation Offset
The ‘X’ in the ‘Scenario Name’ column in Table 8 refers to the prior outage simulated for each scenario. A
list of the prior outages simulated for each scenario in the Stability Analysis is shown in Table 9.
Table 9: Stability Analysis Prior Outages
#
1
2
3
4
5
6
7
8
9
10
Prior Outage
System Intact
Goose Creek-Sheridan 230
Arvada-Dryfork 230
Dryfork-Carr Draw 230 RB
Dryfork-Hughes 230 RB
Buffalo-Carr Draw 230
Wyodak-Carr Draw 230
Carr Draw-Barber Creek 230
Barber Creek-Pumpkin Buttes 230
Pumpkin Buttes-Teckla 230
#
11
12
13
14
15
16
17
18
19
20
Prior Outage
Pumpkin Buttes-Dave Johnston 230
Teckla-Antelope
Donkey Creek-Reno 230
Donkey Creek-Pumpkin Buttes 230
Wyodak-Donkey Creek 230
Wyodak-Osage 230
Wyodak-Hughes 230
Westhill-Stegall 230
Wyodak Unit
Dryfork Unit
* RB indicates Dryfork runback
6.3 Stability Fault Descriptions
In addition to a disturbance-free steady state simulation, each dispatch scenario for the 2011 light winter load
case was simulated with various faults applied. Table 10 lists the faults and the load cases in which they were
applied.
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BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
13
Table 10: Stability Analysis Fault Descriptions
Fault Description
3 PH Bus Fault
Cleared Element
Wyodak 230
Wyodak-Carr Draw 230 line
Wyodak 230
Wyodak-Donkey Crk 230 line
Wyodak 230
Wyodak-Hughes 230 line
Wyodak 230
Wyodak-Osage 230 line
Dryfork 230
Dryfork-Hughes 230 line
Dryfork 230
Dryfork-Carr Draw 230 line
Dryfork 230
Dryfork-Tongue River 230 line
Donkey Crk 230
Donkey Creek-Reno 230 line
P. Buttes 230 kV
P. Buttes-Carr Draw 230 line
Donkey Crk 230
P. Buttes-Donkey Crk 230 line
P. Buttes 230
P. Buttes-Donkey Crk 230 line
P. Buttes 230
P. Buttes-Teckla 230 line
P. Buttes 230
P. Buttes-DJ 230 line
Westhill 230
Westhill-Stegall 230 line
Teckla 230
Teckla-DJ 230 line
7
Fault Type
Fault Duration
3Φ
3Φ
3Φ
3Φ
3Φ
3Φ
3Φ
3Φ
3Φ
3Φ
3Φ
3Φ
3Φ
3Φ
3Φ
4.25 cycles
4.25 cycles
4.25 cycles
4.25 cycles
4.25 cycles
4.25 cycles
4.25 cycles
4.25 cycles
4.25 cycles
3.50 cycles
3.50 cycles
4.25 cycles
4.25 cycles
4.25 cycles
4.25 cycles
Stability Analysis Results
There were no stability performance criteria violations observed on the transmission system as a result of the
interconnection of the proposed project. All post-contingent voltage dips remained well above the established
limit and rotor angle oscillations were positively damped. Additionally, there were no frequency excursions
below the 59.6 HZ limit for a period of 6 cycles or more at any of the monitored buses. The faults simulated at
the Pumpkin Buttes 230 kV bus confirmed the stated LVRT capability of the GE 1.5 MW machines and
exhibited performance that met FERC LVRT requirements.
8
TOT 4A/4B Analysis
The TOT 4A/4B analysis performed as a part of the Feasibility Study for the 500 MW project exhibited no
adverse impacts on the paths. The size of the project has since been reduced to 200 MW and the impacts are
assumed to be reduced as well. Therefore the TOT 4A/4B analysis was not performed as part of the SIS. Refer
to the ‘Pumpkin Buttes 500 MW Wind Project Interconnection Feasibility Study’ report for more information.
9
Short Circuit Analysis
The short circuit analysis performed as a part of the Feasibility Study for the 500 MW project exhibited no
adverse impacts on the local transmission system. The size of the project has since been reduced to 200 MW
and the impacts are assumed to be reduced as well. Therefore the short circuit analysis was not performed as
part of the SIS. Refer to the ‘Pumpkin Buttes 500 MW Wind Project Interconnection Feasibility Study’ report
for more information.
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BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
14
10
Conclusions
This report describes the power flow and stability studies performed to determine the impacts of interconnecting
a new 200 MW wind plant at the Pumpkin Buttes 230 kV substation in northeast Wyoming. The
interconnection project as studied is comprised of one hundred thirty-four (134) GE 1.5 MW wind turbine
generators.
There were no negative impacts to the transmission system as a result of the proposed interconnection.
Facilities required for interconnection to the Pumpkin Buttes 230 kV substation are listed in Table 11.
Table 11: Pumpkin Buttes 230 kV Interconnection Costs
Network Upgrades Required for Interconnection
Pumpkin Buttes Line Terminal
Expand the Pumpkin Buttes substation to accommodate
the new interconnection of the Project
ESTIMATED TOTAL COST
ESTIMATED TIME FRAME
$2,000,000
$2,000,000
15 Months
The thermal capacity on the Alcova-CasperLM 115 kV line would need to be increased to at least 109 MVA.
The upgrade would require a CT tap ratio increase at the Casper terminal, which is currently planned as part of
WAPA’s TOT 3 Expansion project. No additional upgrades to the existing transmission system were identified
for the proposed interconnection.
The possibility of increased system voltages may exist due to collector system charging when the transmission
system is lightly loaded and the proposed wind interconnection is not generating. It is the responsibility of the
customer to compensate for any effects of charging that the wind park collector system may have on the
transmission system. Namely, the installation of reactive equipment will be required to mitigate the potential
impacts of the collector system charging. The equipment shall be under the control of the Transmission System
Operator.
All cost estimates include labor and materials for network infrastructure only, and do not reflect any additional
ancillary services that may be necessary. All costs associated with radial transmission and/or equipment from
the point of interconnection (POI) to the generation facility would be the sole responsibility of the customer.
Preliminary cost estimates are subject to change pending a review of detailed design information 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 Point of Delivery. Curtailment of the proposed interconnection project may be necessary under certain
emergency operating conditions.
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BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
15
APPENDIX A
PRELIMINARY ONE-LINE DIAGRAMS
OF
PROPOSED
WIND FARM
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BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
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ONE-LINE REPRESENTATION OF PROPOSED PROJECT
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BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
17
PSS/E EQUIVALENT ONE-LINE REPRESENTATION
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BHBE-G7
Black Hills Power
Interconnection System Impact Study Report
August 21, 2008
18