EL PASO ELECTRIC COMPANY
SHORT CIRCUIT ANALYSIS
FOR XXX’S PROPOSED
GENERATION INTERCONNECTION
El Paso Electric Company
System Operations Department
System Planning Section
August 2006
I.
INTRODUCTION
The interconnection of new generating units into a transmission system will increase the
fault current contribution into the system. Therefore, as part of this Study, a short circuit
analysis was performed to determine if the additional fault current contribution from the
XXX wind generators into the EPE transmission system will cause any of EPE’s existing
substation circuit breakers to exceed their interruption ratings.
II.
SHORT CIRCUIT STUDY MODELING
The wind generation proposed by XXX is sited approximately 53 miles east of EPE’s
Amrad 345 kV substation. Data provided by XXX indicates that the wind turbines will be
interconnected on the Amrad-Artesia 345 kV transmission line through two 150/200/250
MVA, 34.5/345 kV step-up transformers. Each step-up transformer has a positive
sequence impedance of 8.5% and a zero sequence impedance of 9% on a 150 MVA base.
The step-up transformer impedances modeled in the short circuit analysis for both step-up
transformers were:
Z1 (step-up) = 0.0017 + J0.084983 per unit (150 MVA base)
Z0 (step-up) = 0.0018 + J0.089982 per unit (150 MVA base)
Equivalent reactance data for the modeling of the wind machines in EPE’s short-circuit
data base was difficult to obtain from XXX and their consultants. However, Public
Service company of New Mexico (PNM) has experience in modeling wind machines for a
short-circuit analysis and they provided assistance in obtaining a short-circuit model for
these machines. PNM contacted its GE representative, who in turn provided the shortcircuit modeling for the wind generator. GE stated that an official model for the 1.5 MW
turbine has not been developed as of yet. Therefore, they recommended the use of their
1.67 MVA model at a 0.90 power factor to achieve the 1.5 MVA output of each machine.
The following equivalent reactance values for the wind machines were supplied by GE
and modeled in the EPE short circuit data base:
Xd = Direct Axis Synchronous Reactance = 0.28 per unit
X’d = Direct Axis Transient Reactance = 0.28 per unit
X’’d = Direct Axis Subtransient Reactance = 0.28 per unit
R = Direct Axis Resistance = 0.01 per unit
These reactance values were also based on a 150 MVA base and used to model the wind
generator in the short circuit study.
The location of the XXX wind machines on the Amrad-Artesia 345 kV line also required
the line impedances to be recalculated. Therefore, the Amrad-Artesia line was divided
Short Circuit Analysis for XXX’s
Proposed Generation Interconnection
1
El Paso Electric Company
August 2006
into two sections, the Amrad-XXX 345 kV line and the XXX-Artesia 345 kV line. The
line impedance of the Amrad-Artesia line (125.4 miles in length) was proportioned
according to the location of the XXX generators (53 miles east of Amrad Substation).
Therefore, the Amrad-XXX 345 kV line impedance was modeled as 42.3% (53/125.4) of
the total Amrad-Artesia 345 kV line impedance and the XXX-Artesia 345 kV line
impedance was modeled as 57.7% (72.4/125.4) of the total Amrad-Artesia 345 kV line
impedance. The impedances modeled for each of the XXX 345 kV line segments are
shown below:
AMRAD-XXX
LINE IMPEDANCE
XXX-ARTESIA
LINE IMPEDANCE
Z1 =
0.002904 + j 0.025951
Z1 =
0.003966 + j 0.035449
Z0 =
0.024006 + j 0.092644
Z0 =
0.032794 + j 0.126556
In addition to the new XXX generation, all existing and proposed third party generation
ahead of the XXX project in the study queue were modeled in the data base. These
generation projects included the following:
•
•
•
•
•
570 MW of existing generation (Luna Energy Facility) interconnected at Luna 345 kV
Substation and scheduled to WECC.
141 MW of existing generation (Afton) interconnected at Afton 345 kV Substation
and scheduled through EPE’s Arroyo PST.
60 MW of existing generation interconnected at Tri-State Generation and
Transmission Association, Inc.’s (Tri-State) Hidalgo 115 kV Substation and scheduled
to WECC.
80 MW of existing generation interconnected at Texas-New Mexico Power
Company’s (TNP) Lordsburg 115 kV Substation and scheduled to WECC.
94 MW of generation (presently being constructed) interconnected at Afton 345 kV
Substation and scheduled to WECC.
Two cases were developed to perform this analysis, one with and one without the XXX
generation. Three phase and single-line-to-ground faults were then simulated at the
Amrad and Artesia 345 kV buses in each of the two cases. The difference between the
fault current values in the two cases is the additional fault current contribution from the
XXX wind generation.
Fault currents were monitored at the buses closest to where the XXX generation will be
interconnected, since this is where the greatest fault current contribution can be attributed
to the XXX project. The buses monitored included the following:
Short Circuit Analysis for XXX’s
Proposed Generation Interconnection
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El Paso Electric Company
August 2006
Amrad 345 kV
Amrad 115 kV
Artesia 345 kV
Caliente 345 kV
Caliente 115 kV
The resulting fault currents were then compared to the circuit breaker interruption ratings
of the breakers at each of the above mentioned substations.
III.
RESULTS OF THE SHORT CIRCUIT ANALYSIS
The following is a list of existing circuit breakers and their interruption ratings at each of
the substations monitored in this study:
Breaker
Substation
Amrad
Amrad
Caliente
Caliente
Artesia
Breaker
Voltage
345
345
345
345
115
115
115
115
Number
2438B
6348B
2968B
0388B
7806B
6736B
8766B
0186B
345
345
345
345
345
115
115
115
115
115
115
115
115
115
1828B
3928B
0428B
4178B
4688B
6206B
8616B
0756B
9406B
1536B
6316B
5936B
6186B
6216B
40,000
40,000
40,000
40,000
40,000
40,000
40,000
40,000
40,000
40,000
40,000
40,000
40,000
40,000
345
345
4R10
4R05
40,000
40,000
Short Circuit Analysis for XXX’s
Proposed Generation Interconnection
3
Interruption
Rating (Amps)
40,000
40,000
40,000
40,000
40,000
40,000
40,000
40,000
El Paso Electric Company
August 2006
The short circuit analysis was first performed without the XXX generation interconnected
into the EPE system, but with all other third party generation projects in. This analysis
produced the “base case” short-circuit values of the existing system. The proposed XXX
generation was then modeled into the system and a short-circuit analysis was again
performed with the XXX generation installed. The incremental difference between the
two cases determined the increase in short-circuit contribution to the existing EPE
transmission system due to the proposed XXX generators. If this incremental difference
causes any of the existing substation circuit breakers to exceed their maximum
interruption ratings, they will have to be replaced.
In addition to the buses shown above, faults were simulated at the XXX 345 kV and XXX
34.5 kV buses. This was done to provide XXX with an estimate of the fault current
contribution from the wind machines during a contingency of the XXX wind generation.
This will give XXX an indication of the size of circuit breakers it will need to protect its
34.5 kV and 345 kV buses. The short circuit (fault) currents with and without the XXX
generation at the buses listed above are shown below:
Three Phase Line to Ground:
Without XXX Gen
Fault Current
Faulted Bus
(Amps)
Amrad 345 kV Bus
3,507
Amrad 115 kV Bus
7,000
Caliente 345 kV Bus
6,599
Caliente 115 kV Bus
14,760
Artesia 345 kV Bus
1,507
XXX 34.5 kV Bus
XXX 345 kV Bus
-
With XXX Gen
Fault Current
(Amps)
4,683
8,004
7,481
15,632
2,035
42,176
3,628
Single Phase Line to Ground:
Faulted Bus
Amrad 345 kV Bus
Amrad 115 kV Bus
Caliente 345 kV Bus
Caliente 115 kV Bus
Artesia 345 kV Bus
XXX 34.5 kV Bus
XXX 345 kV Bus
Short Circuit Analysis for XXX’s
Proposed Generation Interconnection
Without XXX Gen
Fault Current
(Amps)
3,082
5,976
6,328
15,842
965
-
4
With XXX Gen
Fault Current
(Amps)
4,239
7,062
6,965
16,593
1,475
36,988
3,672
El Paso Electric Company
August 2006
IV. Results and Conclusions
This short circuit analysis was performed on the EPE system comparing the maximum
fault current on the system at various substations both with and without the proposed
XXX generation. The table below shows the results of the short circuit analysis with the
proposed XXX generation interconnected into the EPE transmission system.
Short Circuit Results With Proposed XXX Generation
Bus
Amrad 345 kV Bus
Amrad 115 kV Bus
Caliente 345 kV Bus
Caliente 115 kV Bus
Artesia 345 kV Bus
XXX 345 kV Bus
XXX 34.5 kV Bus
Maximum
Circuit Breaker
Interruption Rating
(AMPS)
40,000
40,000
40,000
40,000
40,000
-
Maximum
Fault Current With
XXX Generation
(AMPS)
4,683
8,004
7,481
16.593
2,035
3,672
42,176
Results of the analysis indicate that the maximum fault currents are well within the
maximum circuit breaker ratings at each of the buses analyzed. Therefore, the
interconnection of the XXX wind machines into the EPE transmission system as modeled
in this analysis will not cause any existing EPE circuit breaker to operate outside its
interruption rating limit. The results also indicate that XXX will need to install 50,000
Amp circuit breakers at its 34.5 kV bus to protect its system in the event of a loss of all its
wind generation.
Short Circuit Analysis for XXX’s
Proposed Generation Interconnection
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El Paso Electric Company
August 2006
V. Certification
This Short Circuit Analysis was performed as part of the Generation Interconnection
Feasibility Study requested by XXXXXXXXXXXXXXXXXXX (XXX). The step-up
transformer data was supplied by XXX. The model for the wind machine was provided
by Public Service Company of New Mexico’s (PNM) representative from General
Electric (GE). GE stated that it presently does not have an official short-circuit model for
XXX’s proposed 1.5 MVA wind machines. The model they provided was for a 1.67 MVA
wind machine at a 0.90 power factor to achieve the 1.5 MVA rating of each of the XXX
wind machines. This was the best data available to model the XXX wind turbines into the
sort-circuit data base at the time the study was performed. If XXX decides to continue
with its proposed interconnection, it will need to provide a more accurate representation of
the wind machines in order for EPE to perform a more accurate short-circuit analysis of its
transmission system with the XXX generation installed. This Short Circuit Analysis was
performed by El Paso Electric Company (EPE).
Name:
Dennis H. Malone
Title:
Manager, System Planning
Signature:
Company: El Paso Electric Company
Date:
Short Circuit Analysis for XXX’s
Proposed Generation Interconnection
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El Paso Electric Company
August 2006