Feasibility Study
XXXXXX Solar Generation
May 14, 2013
Feasibility Study
XXXXXX Solar Generation
Prepared for
El Paso Electric Company
Prepared by
TRC Engineers, LLC
249 Eastern Avenues
Augusta, ME 04330
(207) 621-7000
Project Number: 202327
May 2013
Feasibility Study
XXXXXX Solar Generation
May 14, 2013
FOREWORD
This report was prepared for the project Interconnection Customer, by System Planning at El Paso
Electric Company. Any correspondence concerning this document, including technical and commercial
questions should be referred to:
Dennis Malone
Director – System Planning Department
El Paso Electric Company
100 North Stanton
El Paso, Texas 79901
Phone: (915) 543-5757
Fax: (915) 521-4763
Or
David Gutierrez
Principal Engineer
El Paso Electric Company
100 North Stanton
El Paso, Texas 79901
Phone: (915) 543-4083
Fax: (915) 521-4763
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May 14, 2013
Table of Contents
EXECUTIVE SUMMARY ..................................................................................................................................1
1.0
INTRODUCTION ..............................................................................................................................................5
1.1
2.0
PERFORMANCE CRITERIA .................................................................................................................................5
STUDY METHODOLOGY .............................................................................................................................. 7
2.1 ASSUMPTIONS ..................................................................................................................................................7
2.2 PROCEDURE .....................................................................................................................................................7
2.2.1
Development and Description of Cases .................................................................................................7
2.2.2
XXXXXX Solar PV Generation Modeling .............................................................................................. 8
2.2.3
Contingency List ....................................................................................................................................8
3.0
STEADY STATE POWER FLOW ANALYSIS ............................................................................................. 9
3.1 PRE-PROJECT POWER FLOW EVALUATION .......................................................................................................9
3.1.1
Pre-Project N-0 Flow Violations ...........................................................................................................9
3.1.2
Pre-Project N-1 Flow Violations ...........................................................................................................9
3.2 POST-PROJECT POWER FLOW EVALUATION .....................................................................................................9
3.2.1
Post-Project N-0 Power Flow Analysis .................................................................................................9
3.2.2
Post-Project N-1 Power Flow Analysis .................................................................................................9
3.3 POWER FLOW ANALYSIS CONCLUSION .......................................................................................................... 11
4.0
STEADY STATE VOLTAGE ANALYSIS ................................................................................................... 12
5.0
SHORT CIRCUIT ANALYSIS ...................................................................................................................... 13
5.1
5.2
5.3
5.4
6.0
SHORT CIRCUIT ANALYSIS MODELING .......................................................................................................... 13
SHORT CIRCUIT ANALYSIS PROCEDURE......................................................................................................... 15
SHORT CIRCUIT ANALYSIS RESULTS .............................................................................................................. 16
SHORT CIRCUIT ANALYSIS CONCLUSIONS ..................................................................................................... 16
DISTRIBUTION ANALYSIS ......................................................................................................................... 17
6.1 GENERAL REQUIREMENTS ............................................................................................................................. 17
6.1.1
IEEE Standards ................................................................................................................................... 17
6.1.2
Noise and Harmonics........................................................................................................................... 17
6.2 VOLTAGE FLICKER ANALYSIS........................................................................................................................ 17
6.3 TRANSIENT STABILITY ANALYSIS .................................................................................................................. 19
6.3.1
Transient Stability Study Case Development ....................................................................................... 20
6.3.2
Transient Stability Analysis Results ..................................................................................................... 20
6.3.3
Transient Stability Analysis Conclusion .............................................................................................. 20
7.0
COST ESTIMATES ........................................................................................................................................ 22
7.1
GENERAL COST ASSUMPTIONS ...................................................................................................................... 22
8.0
DISCLAIMER .................................................................................................................................................. 23
9.0
CONCLUSIONS .............................................................................................................................................. 24
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List of Figures
Figure 6-1 .... IEEE Flicker Curve................................................................................................................ 18
List of Tables
Table 0-1
Table 3-1
Table 3-2
Table 5-1
Table 5-2
Table 5-3
Table 6-1
Table 6-2
Table 6-3
Table 6-4
Table 6-5
Cost Estimate .......................................................................................................................... 3
Pre-Project 2014 N-1 Flow Violations .................................................................................... 9
2014 N-1 Post-project Power Flow Analysis Results ........................................................... 10
Generator Short Circuit Modeling Data ................................................................................ 14
Distribution Line ................................................................................................................... 14
2014 XXXXXX Solar Generation Short Circuit Summary Results ..................................... 16
Voltage Flicker at the POI Due to Project............................................................................. 19
Frequency of Voltage Flicker Due to PV Output Changes ................................................... 19
Generator Models Used for Studies ...................................................................................... 20
Stability Post-Project Case Scenarios ................................................................................... 20
2014 Stability Analysis Results for both Peak and Off-Peak Cases ..................................... 21
Appendices
Appendix A
Appendix B
Appendix C
Project 202327
XXXXXX Solar Feasibility Study Statement of Work
Power Flow Contingency List
Stability Plots
iii
Feasibility Study
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May 14, 2013
EXECUTIVE SUMMARY
The objective of this Feasibility Study (Study) was to determine the impact that the proposed XXXXXX
Solar generation (the Project) for 10 MW (net output) of Photovoltaic (PV) generation, interconnecting to
the 13.8 kV bus of the future Patriot 115/13.8 kV substation, would have on the El Paso Electric
Company (EPE) and Southern New Mexico transmission systems, as well as the EPE future Patriot
Substation distribution system. The requested Commercial Operation date for this project is July 15,
2014.
Three (3) interconnection projects in the EPE study queue that have signed Interconnection Agreements
(IA) with EPE were included in this Study. The three (3) interconnection projects included in this SIS
are:
1.
2.
3.
Montana Power Station: 420 MW gas fired combustion turbine project with varying inservice dates located 2 miles east of the Caliente 345/115 kV substation.
DS92S: 92 MW solar powered project interconnected to the Diablo-Santa Teresa 115 kV
line, 5.7 miles from Diablo 115 kV station.
AA100W: 100 MW wind powered project interconnected to the Amrad-Artesia 345 kV line,
65 miles east of Amrad 345 kV substation.
The generation from the DS92S project was modeled as delivered to all entities in the Western Electricity
Coordinating Council (WECC) except EPE, while the generation from the AA100W was modeled to
deliver to all WECC entities except EPE and New Mexico. The Montana Power Station project was
modeled as delivered to local EPE network load.
The Study Area was limited to the WECC Area 11 - EPE (TX) and Area 10 - PNM (NM).
Steady State Transmission Results
The power flow analysis was conducted using 2014 peak and off peak load conditions. The off peak load
conditions were modeled as fifty percent (50%) of the peak load. The Arroyo Phase Shifter was modeled
as being out of service in both peak and off peak cases. The power flow analysis results showed that the
addition of the 10 MW of Project generation would not require any network upgrades to the EPE and
Southern New Mexico transmission systems, as modeled in the 2014 peak and off peak load flow cases.
The 10 MW of Project generation will be used primarily to feed the load (9.8 MW under 2014 Peak
conditions) at the future 13.8 kV Patriot bus, therefore there will be very little export to the 115 kV EPE
transmission system in the area.
The analysis showed that the XXXXXX Solar generation does not have an adverse impact on the EPE
and Southern New Mexico transmission systems.
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Short Circuit Results
A short circuit analysis was performed to determine if the addition of the XXXXXX Solar generation to
the EPE transmission system would cause any of the existing substation circuit breakers on EPE’s
transmission system to exceed their interrupting capability ratings.
The results of this short circuit study showed that the maximum fault currents with the XXXXXX Solar
project in service did not exceed any of the breaker interrupting capabilities on the EPE transmission
system.
Distribution Results
Several analyses were performed to determine if the addition of the XXXXXX Solar generation would
have any adverse effects on El Paso’s underlining distribution system in the immediate Study Area.
These analyses included a closer look at the requirements necessary to interconnect and model PV
generation under IEEE standards, the impact of changes in sun exposure at the solar farm, and a transient
stability analysis on the distribution system in the immediate Project Area.
The analysis showed that the XXXXXX Solar generation does not have an adverse impact on the
immediate EPE distribution system in the project area.
Cost Estimates
Good faith cost estimates are presented. The cost estimates are in 2013 dollars (no escalation applied)
and are based upon typical construction costs in the area. These costs include all estimated applicable
labor and overheads associated with the engineering, design, and construction of any new EPE facilities.
These estimates did not include the Generator Interconnection Costs1 for any other Interconnection
Customer owned equipment or associated design and engineering except for the Point of Interconnection
(POI) facilities.
The estimated total cost for the required upgrades is $635,000. This breaks down to $635,000 for the
EPE Interconnection Costs2 and $0 for Network Upgrades Cost3. Generator Interconnection Costs have
not been estimated as part of this study. Table 0-1 details the cost per facility.
1
Generator Interconnection Costs: cost of facilities paid for by Interconnection Customer and owned and
operated by the Interconnection Customer from the generator facilities to the Change of Ownership Point, which is
typically on the first dead-end at the Point of Interconnection substation. Not subject to transmission credits.
2
EPE Interconnection Costs: cost of facilities paid for by Interconnection Customer but owned and
operated by EPE from the Change of Ownership Point to the Point of Interconnection. Not subject to
transmission credits.
3
Network Upgrades Cost: Cost of facilities from the Point of Interconnection outward, paid for by the
interconnector but owned and operated by EPE. Subject to transmission credits.
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Table 0-1 Cost Estimate
Facility
Patriot 13.8 kV Station
Construction
(Including: Voltage
Regulators; Switchgear
Expansion; Breakers; and
Labor)
Construction of a 1.5 mile
13.8 kV line connecting the
Project to the future
Patriot 13.8 kV Bus
Distribution: Metering,
Switches; Protective
Equipment
Underground Getaway and
Material
TOTAL
Generator
Interconnection Cost
EPE
Interconnection
Cost
Network
Upgrade Cost
Total
N/A
$230,000
N/A
$230,000
N/A
$290,000
N/A
$290,000
N/A
$85,000
N/A
$85,000
N/A
$30,000
N/A
$30,000
N/A
$635,000
$0
$635,000
The estimated time frame for Engineering, Procurement, and Construction of Network Upgrades is
approximately 12 months upon notice to proceed with construction from the Interconnection Customers.
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Figure 0-1 Below details the interconnection.
Figure 0-1: XXXXXX Solar POI and Future Patriot 13.8 Substation One-line
Unit 1
10 MW PV
Patriot Solar PV
Generating Site
13.8/0.69 kV
Wye-Grounded/Wye-Grounded
10 MVA Transformer
(Six 1.5 MVA and One 1 MVA)
0.69 kV
Change of
Ownership
Disconnect Switch
13.8 kV
Revenue
Metering
13.8 kV 1.5 Mile Express Line
M
EPE Load
13.8 kV
Point of
Interconnection
115 kV
To
Cromo
Patriot
Substation
To
Newman
Color Code
Network Upgrades
Existing Facilities
EPE Interconnection Facilities
Interconnection Customer Equipment
Conclusion
This Feasibility Study showed that the proposed XXXXXX Solar generation will not have an adverse
impact on the EPE and Southern New Mexico transmission systems or the EPE Patriot distribution
system.
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1.0
INTRODUCTION
The Interconnection Customer proposed the interconnection of 10 MW of solar PV generation to the 13.8
kV bus of EPE’s future Patriot 115/13.8 kV substation. The FERC Open Access Transmission Tariff
(OATT), under the Small Generator Interconnection Procedures (SGIP), requires that a Feasibility Study
be performed for Interconnection Customers who desire to interconnect their generation facilities to a
Transmission Provider’s transmission system. The proposed Commercial Operation date for the
XXXXXX Solar project is July 15, 2014.
1.1
Performance Criteria
The Study was performed according to Western Electricity Coordinating Council (WECC), North
American Electric Reliability Corporation (NERC), and EPE standards. The EPE local reliability
standards can be found in Section 4 of EPE’s FERC Form No. 715. The steady state analysis was
performed using the GE PSLF Version 18 software.
Transformer tap and phase-shifting transformer angle movement, as well as static VAR device switching
were allowed to move for the steady state pre-contingency analysis. All regulating equipment such as
transformer controls and switched shunts were fixed at pre-contingency positions when the contingency
analysis was performed. All facility loadings, as well as bus voltages 69 kV and greater, were monitored
within the El Paso, New Mexico and Arizona control areas.
Pre-contingency flows on lines and transformers were required to remain at or below the normal rating,
while post-contingency flows on lines and transformers were required to remain at or below the
emergency rating. Flows above 100% of an element’s rating, either pre- or post-contingency, were
considered violations.
Post-project voltage criteria violations that did not exacerbate or improve an existing pre-project violation
were not considered an adverse impact to the system.
The performance criteria utilized in identifying violations in the study area are shown in Table 1.
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Table 1-1 EPE and New Mexico Performance Criteria
Area
Conditions
Normal
(ALIS)
Loading
Limits
Normal Rating
Voltage (p.u.)
Voltage
Drop
0.95 - 1.05
0.95 - 1.10
69 kV and above
Artesia 345 kV
0.95 - 1.08
Arroyo 345 kV PST source side
0.90 - 1.05
EPEC
Contingency
Emergency
Rating
0.925 - 1.05
0.95 - 1.07
0.95 - 1.08
7%
7%
7%
0.90 - 1.05
0.95 - 1.05
PNM
TriState
Normal
(ALIS)
Contingency
N-1
Contingency
N-2
Normal
ALIS
Contingency
N-1
Contingency
N-2
Application
7%
Alamo, Sierra Blanca and Van
Horn 69 kV
60 kV to 115 kV
Artesia 345 kV
Arroyo 345 kV PST source side
Alamo, Sierra Blanca and Van
Horn 69 kV
Hidalgo, Luna, or other 345 kV
buses
Normal Rating
0.95-1.05
Emergency
Rating
Emergency
Rating
0.925-1.08***
0.90 – 1.08***
6 %**
6 %**
46 kV to 115 kV
230 kV and above
0.90-1.08***
10 %
46 kV and above*
Normal Rating
0.95-1.05
Emergency
Rating
Emergency
Rating
46 kV and above*
All buses
0.90 – 1.10
6%
0.90-1.10
7%
0.90-1.10
10%
Tri-State buses in the PNM
Service Area (list provided by
Tri-State)
Tri-State buses in southern and
northeastern New Mexico (list
provided by Tri-State)
*
All buses
Taiban Mesa and Guadalupe 345 kV bus voltage must be between 0.95 and 1.10 p.u. under normal and
contingency conditions.
** For PNM buses in southern New Mexico, the allowable N-1 voltage drop is 7%.
*** Provided operator action can be utilized to adjust voltages back down to 1.05
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2.0
2.1
STUDY METHODOLOGY
Assumptions
The following assumptions are consistent for all study scenarios unless otherwise noted.

This study assumed that all system expansion projects as planned by area utilities by the year
under analysis are completed, and that any system improvements required by the interconnections
senior to the Project generation are implemented.

This study did not analyze any transmission service from the interconnection point to any specific
point on the grid for the interconnections senior to the Project generation.
2.2
Procedure
The Study included only Steady State Analysis as stated in Section 6.0 of the EPE Small Generator
Interconnection Procedures Feasibility Study Agreement. A description of the procedures used to
complete the analyses is presented below.
2.2.1
Development and Description of Cases
A 2014 WECC power flow case at 100% summer peak load was used and modified, as listed below, to
establish a 2014 benchmark case without the proposed XXXXXX Solar generation. The 10 MW
XXXXXX Solar generation was modeled as being dispatched to serve EPE system native load. The
Arroyo Phase Shifter was modeled out of service as it is not planned to be completed until after the 2014
study year.
The off-peak case was created by reducing the WECC Area 11 (EPE) and Area 10 (PNM, TSGT) loads
and generation by 50% and adjusting area interchange.
2.2.1.1
Benchmark 2014 Cases:
The 2014 benchmark, peak and off-peak cases included the following existing third party generation:
(a) 420 MW of generation (Montana Power Station) with varying in-service dates
interconnected to the Caliente 115 kV bus and scheduled to EPE native load.
(b) 92 MW of generation (DS92S) interconnected on the Diablo-Santa Teresa 115 kV line,
5.7 miles from Diablo 115 kV station and scheduled to all WECC except EPE.
(c) 100 MW of generation (AA100W) interconnected on the Amrad-Artesia 345 kV, 65
miles east of Amrad 345 kV substation and scheduled to all WECC entities except EPE
and New Mexico.
(d) Peak and off-peak 2014 post-project cases were created from the benchmark cases as
described above.
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2.2.2
May 14, 2013
XXXXXX Solar PV Generation Modeling
The XXXXXX Solar generation consisting of 10 MW from a yet unknown number of PV inverters, was
modeled as being interconnected at a new XXXXXX Solar 13.8 kV bus (POI) via a 1.5 mile express
feeder from the Patriot 13.8 kV Substation bus. The 10 MW of solar PV generation was modeled as a
single 10 MW unit at 0.69 kV, stepped up to 13.8 kV at the Solar Farm (POI).
The generator step-up (GSU) transformers (0.69 kV/13.8 kV) information provided (6 GSUs at 1.5 MVA
and 1 GSU at 1.0 MVA are mentioned in the interconnection application) calls for an aggregate of 10
MVA normal and emergency ratings to be used. Provided that the planned Project generation operates at
10 MW, these individual GSUs will be overloaded if the Project is at maximum output and providing the
required +/-0.95 Power Factor (PF) of VAR support to EPE system. EPE directed that this study was to
be performed assuming a Unity PF for the Project generation. The Project output and GSU specification
should be confirmed before this Project proceeds. If the EPE required +/-0.95 PF is adhered to, the
individual GSU’s will overload. Furthermore, the interconnection application also states that these
GSU’s will be Wye-Delta (low to high) configurations. This configuration will need to be changed, such
that the interconnecting high side is a grounded Wye.
2.2.3
Contingency List
All outages (69 kV and above within EPE) were modeled in the subsystem files. The list of contingencies
used in this study is included in Appendix B. These contingencies were selected to represent a good cross
section of potential contingencies that would stress the EPE and PNM’s southern New Mexico systems.
This study was only performed for N-0 and N-1 conditions.
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3.0
3.1
STEADY STATE POWER FLOW ANALYSIS
Pre-Project Power Flow Evaluation
Peak and off peak base cases were evaluated for overloaded facilities under both normal and contingency
conditions prior to the addition of the XXXXXX Solar generation.
3.1.1
Pre-Project N-0 Flow Violations
Power flow study analysis results showed no transmission facilities were overloaded in the EPE, PNM, or
Tri-State (TSGT) areas under pre-contingency system conditions prior to the addition of the XXXXXX
Solar generation.
3.1.2
Pre-Project N-1 Flow Violations
Power flow contingency analysis results showed that few overloads existed in El Paso prior to the
addition of the Patriot generation, as shown in Table 3-1.
Table 3-1 Pre-Project 2014 N-1 Flow Violations
From Bus
kV
To Bus
kV
Ckt
ID
Area
Rating
(MVA)
DONA_ANA
(*)
115
PICACHO
115
1
11
80.0
JORNADA
115
ARROYO
115
1
11
35.0
JORNADA
115
ARROYO
115
1
11
35.0
Contingency
LUNA-MIMBRES
115 kV
LE1-JORNADA
115 kV
LE1-ARROYO
115 kV
Off
Peak
Peak
% of Emergency
Rating
48.3
118.6
101.9
100.9
104.4
113.2
(*) – Denotes that this line is owned by Tri-State.
3.2
Post-Project Power Flow Evaluation
The inclusion of the XXXXXX Solar generation showed no adverse effects to the El Paso and New
Mexico areas. The post-project analysis was performed under both normal and contingency conditions.
3.2.1
Post-Project N-0 Power Flow Analysis
Power flow study results for the EPE and PNM areas showed that the addition of the XXXXXX Solar
generation to the existing system would not cause any power flow violations under non-contingency
system conditions.
3.2.2
Post-Project N-1 Power Flow Analysis
Power flow study results for the EPE and PNM areas showed that the addition the XXXXXX Solar
generation to the existing system would not have an adverse impact on the El Paso and New Mexico
transmission systems, as shown in 3-2.
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Table 3-2 2014 N-1 Post-project Power Flow Analysis Results
Peak or
Off-peak
From Bus
kV
To Bus
kV
Ckt
ID
Area
Rating
(MVA)
Contingency
Peak
Peak
Off-peak
Off-peak
JORNADA
DONA_ANA
JORNADA
JORNADA
115
115
115
115
ARROYO
PICACHO
ARROYO
ARROYO
115
115
115
115
1
1
1
1
11
10
11
11
35.0
80.0
35.0
35.0
LE1-JORNADA 115 kV
LUNA-MIMBRES 115 kV
LE1-JORNADA 115 kV
LE1-ARROYO 115 kV
Project 202327
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Without
Project
% of
Rating
100.89
118.58
101.93
104.35
With
Project
% of
Rating
100.90
118.62
101.96
104.37
Delta %
of Rating
0.01
0.05
0.03
0.02
Feasibility Study
XXXXXX Solar Generation
3.3
May 14, 2013
Power Flow Analysis Conclusion
The analysis showed that the addition of the XXXXXX Solar generation to the system would not have an
adverse impact on the EPE or New Mexico transmission systems. For the peak load case, the 9.8 MW
load as modeled at the 13.8 kV Patriot Bus keeps the 10 MW of Project generation local to the 13.8 kV
distribution system without flowing onto the 115 kV transmission system in the area. Depending upon
the protection scheme at the Patriot Substation, this may create a possibility of islanding for loss of the
13.8/115 kV transformer.
For the off-peak case, EPE should expect back flow on to the 115 kV system from the Project.
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4.0
STEADY STATE VOLTAGE ANALYSIS
Bus voltages within the Study Area were compared under both normal and contingency conditions, with
and without the XXXXXX Solar generation in service. The Performance Criterion shown in Table 1 was
considered when analyzing bus voltages for violations.
The voltage analysis results showed that after the addition of the XXXXXX Solar generation, the Study
area transmission network voltages stayed within criteria limits or did not significantly change from the
pre-project voltage levels. See Appendix C for detailed results.
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5.0
SHORT CIRCUIT ANALYSIS
A short circuit analysis was performed to determine if the addition of the XXXXXX Solar generation to
the EPE transmission system would cause any of the existing substation circuit breakers on EPE’s
transmission system to exceed their interrupting capability ratings.
5.1
Short Circuit Analysis Modeling
Pre and post-project cases were developed to perform this analysis showing the impact of the integration
of the XXXXXX Solar generation on the circuit breakers in the EPE transmission system. As mentioned
in earlier sections, any planned or proposed third party generation listed in EPE’s study queue ahead of
the Project were also modeled in the two cases. The generator data used in the study is shown in Table 51 and the impedance data used for the 1.5 mile distribution line is shown in Table 5-2.
This analysis evaluated the impact of the XXXXXX Solar generation by comparing the pre- and postXXXXXX Solar generation fault current levels.
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Table 5-1 Generator Short Circuit Modeling Data
Total
Output
(MW)
Project
AA100W
100
DS92S
92
Interconnection Customer
GSU
Unit
ID
Pmax
(MW)
Qmax
(MVAR)
Qmin
(MVAR)
Z subtransient
(p.u)
Rating
(MVA)
Voltage
(kV)
Z Subtransient
(p.u)
P1
60
20
-20
0.00 +j 0.0213
100
345/34.5
0.0037 +j0.1667
P2
40
13
-13
0.00 +j 0.0213
G1
46
24
-17.2
0.00 +j 0.1200
56
115/13.8
0.0000 +j0.085
G2
46
24
-17.2
0.00 +j 0.1200
56
115/13.8
0.0000 +j0.085
10
13.8/0.69
0.0000 +j0.133
XXXXXX Solar
10
G1
10
0
0
*0.00 +j0.1200
Generation
* - Denotes that subtransient impedance values were not available, so default values found in ASPEN were used.
Table 5-2 Distribution Line
From Bus
XXXXXX Solar
Project 202327
To Bus
Patriot
kV
13.8
Ckt. ID
Line Impedance (p.u)
Length (mi.)
1
1.5
14
R1
X1
R0
X0
0.0035
0.0075
0.0035
0.0075
Feasibility Study
XXXXXX Solar Generation
5.2
May 14, 2013
Short Circuit Analysis Procedure
The initial short circuit analysis was performed with all other third-party generation projects ahead of the
XXXXXX Solar generation in the study queue in service and XXXXXX Solar generation out of service.
This identified the “base case” fault duties of the circuit breakers. The short circuit analysis was
performed again with XXXXXX Solar generation in service on the 2014 ASPEN One Liner case
provided by EPE.
Three phase, two phase, and single-phase line-to-ground faults were simulated at selected buses in the
EPE system with terminal voltages at 69 kV and above. EPE also requested faults on all transformer
tertiary buses. ASPEN One Liner and Batch Short Circuit Module were used to perform the short circuit
analysis. The short circuit fault analyses were performed with the following settings:




Transmission line G+jB ignored.
Shunts with positive sequence impedance ignored.
Transformer line shunts ignored
The pre-fault voltage was calculated using a Flat bus voltage of 1.05 per unit.
The difference between the fault current values in the two cases demonstrates the post-project fault
contribution of the XXXXXX Solar generation to the pre-project fault current levels in the EPE system.
The resulting fault currents in the post-project scenario were compared to the lowest breaker interruption
ratings at each of the substations to determine whether or not the XXXXXX Solar project caused any
adverse impact.
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5.3
May 14, 2013
Short Circuit Analysis Results
The results of this short circuit study showed that the existing maximum fault currents (without the
XXXXXX Solar generation in service) exceeded the breaker interrupting capability at some substations.
These are existing criteria violations that EPE is currently addressing, and will not be discussed in this
report.
The short circuit analysis results for the monitored buses in the immediate EPE Project area (2 busses
away) are shown below in Table 5-3 below.
Table 5-3 2014 XXXXXX Solar Generation Short Circuit Summary Results
Bus Fault On:
5.4
Lowest
Breaker
Rating
(kA)
CROMO 115kV
40
NEWMAN 115kV
50
PATRIOT 13.8kV
TBD
PATRIOT 115kV
TBD
XXXXXX SOLAR 13.8kV
TBD
Fault
Pre
Current
(kA)
Pre X/R
Post
Current
(kA)
Post X/R
Delta
(Amps)
3LG
2LG
1LG
3LG
2LG
1LG
3LG
26.6117
25.6656
22.8651
37.3984
42.2266
44.1127
5.3693
11.0043
10.0668
7.79873
55.27
47.7693
42.6066
20.5698
26.6117
25.6656
22.8651
37.398.4
42.226.6
44.112.7
7.232.5
11.0196
10.0793
7.80317
55.6205
48.0246
42.7698
154.26
0.0
0.0
0.0
0.0
0.0
0.0
1863.2
2LG
1LG
3LG
2LG
1LG
3LG
5.4043
5.4276
19.9235
18.8091
15.2239
0.0
20.78
20.9708
7.40832
6.8663
5.10489
0.0
7.2970
7.3386
19.9235
18.8091
15.2239
7.1424
123.681
57.0142
8.33394
7.64196
5.31382
578.423
1892.7
1911.0
0.0
0.0
0.0
7142.4
2LG
1LG
0.0
0.0
0.0
0.0
7.2049
7.2459
438.953
62.1587
7204.9
7245.9
Short Circuit Analysis Conclusions
The results of this short circuit study showed that the post-project fault currents with the XXXXXX Solar
generation on-line increases fault levels at the existing Patriot 13.8 kV bus by approximately 1.9 kA, but
does not cause fault currents to exceed the breaker interrupting capability of any breakers in the EPE
transmission system. Therefore, the project generation does have an adverse impact to the EPE
transmission breaker duties. EPE Substation and Protection Engineering verified the minimal breaker
ratings at all the sites listed in the table.
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6.0
DISTRIBUTION ANALYSIS
Several analyses were performed to determine if the addition of the XXXXXX Solar generation would
have any adverse effects on El Paso’s distribution system fed out of the Patriot Substation in the
immediate Project Area. These analyses included a closer look at the requirements necessary to
interconnect and model PV generation under IEEE standards, the impact of changes in sun exposure at
the solar farm, and a low level transient stability analysis on the immediate Project Area.
6.1
General Requirements
6.1.1
IEEE Standards
The Interconnection Request did not specify the model of PV inverters that will be used for this Project.
However, in order for the Project to move forward to the Facilities Study phase of the Interconnection
process, the PV inverters to be used will need to be specified and adhered to the following IEEE standards
and guidelines:



6.1.2
IEEE Standard 1547-2003, “IEEE Standard for Interconnecting Distributed Resources with
Electric Power Systems.”
UL Standard 1741, “Inverters, Converters and Charge Controllers for Use in Independent Power
Systems.”
IEEE Standard 929-2000, “IEEE Recommended Practice for Utility Interface of Photovoltaic
(PV) Systems.”
Noise and Harmonics
The inverter is certified IEEE 1547, 1547.1 compliant and the Total Harmonic Distortion (THD) is given
at less than 3.0%.
6.2
Voltage Flicker Analysis
Voltage flicker is defined as a voltage variation sufficient in duration to allow visual observation of a
change in electric light intensity of an incandescent light bulb. The IEEE curve showing fluctuations per
time period versus borderline of visibility and borderline of irritation is shown below. The suggested
operating criteria is that the magnitude of voltage flicker must be limited to less than 3% and that the
frequency of flicker fluctuations be less than the border line of irritation boundary.
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Figure 6-1 IEEE Flicker Curve
Clouds shading the PV panels adversely impact the output of a PV system. As a cloud shadow passes
over a PV system the output will decrease due to the reduction in sunlight. The change in PV system
output on a distribution circuit may cause a fluctuation of voltage that might be seen by electric
customers. This fluctuation would be classified as a voltage flicker.
A rapid change in load cannot be compensated by the voltage regulation equipment installed on a
distribution system. Most utilities use a typical time delay setting of 60 seconds for substation LTCs and
90 seconds for line voltage regulators. This time delay means that an LTC or voltage regulator will not
respond to voltage changes until the voltage has been outside of the bandwidth for a low of 60 or 90
seconds. This helps to control “hunting” of the multiple devices trying to control the voltage.
As a cloud passes over a PV system the output will decrease to a lower value. Given the amount of PV
system output reduction due to clouds is not known, the assumption is that it goes to zero and returns to
full output once sunlight returns.
The voltage at the Patriot 13.8 kV Substation bus is anticipated to be fixed at 1.05 p.u. with and without
the Project for peak and off peak load periods. Table 6-1 summarizes the balanced voltage and the
calculated voltage flicker magnitude. Project output will exhibit relatively slow variations due to cloud
cover shading rather than spike between full on and off. Consequently, the results shown in Table 6-1
represent a worst-case scenario, such as a sudden shutdown of the PV plant.
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Table 6-1 Voltage Flicker at the POI Due to Project
Project POI Bus Voltage
Case
Off Peak Load
Peak Load
Without Project
13.68 kV
13.65 kV
With Project*
13.70 kV
13.69 kV
0.1462
0.2930
% Voltage Flicker
NOTE: % Voltage Flicker calculated as ‘With Project’ minus
‘Without Project’ divided by ‘Without Project’ times 100.
*The Project is set to operate at Unity power factor.
Table 6-2 is based on an interpolation of the flicker frequency from the IEEE flicker graph. Cloud
movement is slow; therefore the frequency of the voltage fluctuations will be less than the frequency
limits shown in Table 6-2. The calculated magnitude of the flicker due to the Project is much less than
the 3% limit criterion. The distribution voltage flicker resulting from changes in the Project output is not
anticipated to have an adverse effect.
Table 6-2 Frequency of Voltage Flicker Due to PV Output Changes
Based on GE Flicker Curve
% Voltage Flicker
Border Line of
Visibility
Border Line of
Irritation
0.1462
< 1/sec
< 1/sec
0.2930
< 1/sec
< 1/sec
NOTE: Fluctuation per time period extrapolated from the IEEE flicker graph
6.3
Transient Stability Analysis
EPE requested TRC to take a closer look at the impacts of the Project on their Distribution System in the
Project area. In order to ensure the damping effects of the EPE system in the area, a Transient Stability
Analysis was completed.
The simulations were conducted using the General Electric, Inc. PSLF load flow and dynamic simulation
software package, Version 18. Dynamic stability simulations were conducted for peak and off-peak load
conditions with the XXXXXX Solar generation units on at full capacity and off.
EPE provided the base cases and dynamic file data for this part of the study. The Interconnection
Customer did not provide any data for modeling of their facility. As a result, typical modeling data for
solar facilities was used as per WECC modeling standards. The XXXXXX Solar generation was modeled
as one PV plant with a maximum output of 10 MW.
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Table 6 shows the models used for the studies.
Table 6-3 Generator Models Used for Studies
Project
XXXXXX Solar
6.3.1
Turbine Type
Notes
PSLF Model
Unknown
Used Typical Type 4 Wind
Turbines for model data and
parameters as per WECC
Standards
WT4G, WT4E
Transient Stability Study Case Development
Two base cases were used to simulate Peak and Off-Peak conditions. The analysis compared the system
response to the fault simulations before and after the XXXXXX Solar generation was added. The
dynamic study cases are listed in 6-4.
Table 6-4 Stability Post-Project Case Scenarios
Year
2014
6.3.2
Descriptions
Heavy Load Case
Senior Queued Projects in-service
Arroyo PST out of service
Afton in service
Light Load or Off-Peak Case
Senior Queued Projects in-service
Arroyo PST out of service
Afton out of service
Transient Stability Analysis Results
The stability analysis showed that the EPE Patriot distribution system and the EPE transmission system
remained stable for all simulated faults before and after the addition of the Project.
Simulated fault locations, time durations, and the system response are shown in 6-5. The stability plots
for these faults can be found in Appendix D.
6.3.3
Transient Stability Analysis Conclusion
The study area remains stable and well damped for all the contingencies analyzed.
The Project addition to the system does not pose any concern to system stability performance.
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Table 6-5 2014 Stability Analysis Results for both Peak and Off-Peak Cases
2014
Results
Off Peak Load
#
Fault Location
1
XXXXXX 115kV
2
3
Patriot 115 kV
Patriot 13.8 kV
Project 202327
Event Description
Three Phase fault at XXXXXX 115 kV
bus.
Three Phase fault at Patriot 115 kV bus.
Three Phase fault at Patriot 13.8 kV bus.
Clearing (cycles)
XXXXXX 115 kV= 6.0, Open
XXXXXX-Patriot 115kV Line
Patriot 115 kV= 6.0
Patriot 13.8 kV= 6.0
21
Peak Load
Project
Off
Project
On
Project
Off
Project
On
Stable
Stable
Stable
Stable
Stable
Stable
Stable
Stable
Stable
Stable
Stable
Stable
Feasibility Study
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May 14, 2013
7.0
COST ESTIMATES
Good faith cost estimates have been determined. The cost estimates are in 2013 dollars (no escalation
applied) and are based upon typical construction costs in the area for previously performed similar
construction. These estimated costs include all applicable labor and overheads associated with the
engineering, design, and construction of these new facilities. These estimates did not include the cost for
any other Interconnection Customer owned equipment or associated design and engineering except for
those located at the POI.
The estimated total cost for the required upgrades is $635,000. This breaks down to $635,000 for the EPE
Interconnection Cost4 and $0 for Network Upgrades Cost5. The Generator Interconnection Cost6
estimates are not included.
7.1
General Cost Assumptions
The cost estimates provided are good faith “scoping estimates.”
Estimates do not include land or permitting.
Interconnection Customer to secure POI site and transfer ownership to EPE.
Permitting time frames are included. Actual time frames will vary due to local and Federal
requirements.
5. Estimates are in 2013 U.S. dollars.
6. Where applicable, the Interconnection Customers are responsible for funding and construction of
all transmission facilities from the proposed generator substation to the Points of Interconnection
including disconnect switches, use and reset existing relays, and reset relays at remote ends.
7. Interconnection Customer is responsible for Engineering, Procurement, and Construction for all
and any FACTs and other transmission and distribution compensation devices at their generation
site or along their long interconnecting transmission or distribution lines to just outside the POI
sites.
1.
2.
3.
4.
4
5
6
EPE Interconnection Cost: Cost of facilities paid for by interconnector but owned and operated by EPE
from the Change of Ownership Point to the Point of Interconnection. Not subject to transmission credits.
Network Upgrades Cost: Cost of facilities from the Point of Interconnection outward, paid for by the
interconnector but owned and operated by EPE. Subject to transmission credits.
Generator Interconnection Cost: Cost of facilities paid for by interconnector and owned and operated by the
interconnector from the generator faculties to the Change of Ownership Point, which is typically at
the Point of Interconnection substation first dead-end. Not subject to transmission credits.
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8.0
DISCLAIMER
If any of the project data provided by Interconnection Customer and used in this study varies significantly
from the actual data after the XXXXXX Solar generation equipment is installed, the results from this
study will need to be verified with the actual data at the Project Interconnection Customer's expense.
Additionally, any change in the generation in EPE’s Interconnection Queue that is senior to the
XXXXXX Solar generation may require a re-evaluation of this Study.
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9.0
CONCLUSIONS
This XXXXXX Solar Feasibility Study, consisting of a Steady State, Short Circuit, Transient Stability
and Voltage Flicker Analysis, for a net 10 MW of generation interconnecting to the EPE transmission and
distribution systems has demonstrated that the XXXXXX Solar generation will NOT have an adverse
impact on the EPE and Southern New Mexico transmission systems or the EPE distribution system.
The estimated cost for integrating the XXXXXX Solar generation onto the EPE and Southern New
Mexico transmission systems is $635,000. The good faith estimate of the time frame to Engineer,
Procure, and Construct all facilities is 12 months.
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APPENDIX A
XXXXXX Solar Feasibility Study Statement of Work
Project 202327
Appendix A
Feasibility Study
XXXXXX Solar Generation
May 14, 2013
APPENDIX B
Power Flow Contingency List
Project 202327
Appendix B
Feasibility Study
XXXXXX Solar Generation
May 14, 2013
APPENDIX C
Stability Plots
Project 202327
Appendix C