ERCOT Independent Study

ERCOT Independent Review of the CNP Katy Area Upgrades
Project
Public
ERCOT Independent Review of the CenterPoint Katy Area Upgrades
Project
Version 1.0
© 2014 Electric Reliability Council of Texas, Inc.
System Planning
ERCOT Independent Review of the CenterPoint Katy Area Upgrades Project
ERCOT Public
Document Revisions
Date
05/15/2014
Version
Description
Author(s)
Final
Xiaolong
Yu
Review ed by
Prabhu
Gnanam,
Jeff Billo
1.0
© 2014 Electric Reliability Council of Texas, Inc. All rights reserved.
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ERCOT Independent Review of the CenterPoint Katy Area Upgrades Project
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Table of Contents
1.
Introduction ............................................................................................................................... 1
2.
Study Approach ........................................................................................................................ 2
3.
Reliability Analysis of the Base Case.................................................................................... 2
4.
Reliability Analysis of Project Options ................................................................................. 4
5.
Conclusion ................................................................................................................................. 6
6.
Designated Providers of Transmission Facilities ................................................................. 7
7.
Appendix.................................................................................................................................... 8
© 2014 Electric Reliability Council of Texas, Inc. All rights reserved.
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ERCOT Independent Review of the CenterPoint Katy Area Upgrades Project
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1. Introduction
The Katy area is an established suburban area west of Houston that is expected to experience
significant load growth in the near future. CenterPoint has forecasted the Katy area to serve 1147
MW in 2018 which is an increase of approximately 152 MW from the actual 2013 summer peak
load experienced in the Katy area.
Using the 2018 peak load, under the contingency loss of the Flewellen – Mason Road and Flewellen
– Obrien 138-kV double-circuit line, the Brazos – Flewellen 138-kV line will exceed its emergency
rating. Figure 1 below shows the area of concern.
Figure 1 Area of concern
In order to provide transmission infrastructure that meets ERCOT reliability criteria and increase the
reliability in the Katy area by mitigating the loss of over 300 MW of load following a double circuit
tower outage, CenterPoint Energy proposed the following improvements in the Katy area:

Convert Katy Substation from a double-tap configuration to a loop configuration on 138 kV
circuit 09.
© 2014 Electric Reliability Council of Texas, Inc. All rights reserved.
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ERCOT Independent Review of the CenterPoint Katy Area Upgrades Project
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
Convert Franz Substation from a double-tap configuration to a loop configuration on 138
kV circuit 09.

Construct a new approximately 6.4 mile circuit from Zenith Substation to Franz tap on
double-circuit structures creating a new 138 kV Zenith–Franz–Katy–Flewellen circuit 09.

Install a second 800 MVA normal rated / 1000 MVA emergency rated 345/138 kV
autotransformer at Zenith Substation.

Upgrade 1.6 miles of existing 138 kV circuit from Franz Substation north to the interface
with the new 138 kV circuit to Zenith Substation.
The total cost for these projects is estimated to be $20.4 million and it is anticipated that the projects
can be completed by summer 2017.
2. Study Approach
The analysis of the system primarily focused on the steady-state thermal reliability of the ERCOT
transmission system in the Katy area to meet the projected 2018 load growth . The latest 2013
Regional Transmission Plan (RTP) model for the year 2018 served as the base case of this analysis.
The 2013 RTP identified the Katy area reliability need and a reliability project (2013 RTP # R-62)
was proposed as a place holder solution until a more thorough analysis of the area could be
completed. The 2013 RTP Katy area upgrades project was removed from the base case for this
analysis.
Base case Transmission system changes:

Remove the Zenith – Franz 138 kV line.

Remove the new 800/1000 MVA 345/138 kV autotransformer at Zenith Substation.

Restore the original configurations in and among Substations Katy, Franz, and Freeman, so
the Katy – Franz 138 kV circuit 09 has 280 MVA emergency rating; the Katy – Franz 138
kV circuit 66 has 280 MVA emergency rating; the Franz – Freeman 138 kV circuit 66 has
220 MVA emergency rating. The circuit parameters (R/X/B) are restored accordingly.
As part of the ERCOT independent review, s everal transmission improvement options were studied
and compared in order to identify a reliable while economical solution. The evaluation of these
options mainly consisted of N-1 contingency analysis . In addition, selected G-1+N-1 (single
generator unavailable followed by N-1) contingency analysis and X-1+N-1 (single 345/138 kV
transformer unavailable followed by N-1) contingency analyses were performed in accordance with
NERC and ERCOT reliability criteria.
3. Reliability Analysis of the Base Case
AC N-1 contingency analysis of the base case with the 2018 peak load was performed using
PowerWorld Simulator. Figure 2 below depicts that the flow on the Brazos – Flewellen 138-kV line
is 118% of its 280 MVA emergency rating under the contingency loss of the Flewellen – Mason
Road and Flewellen – Obrien 138-kV double-circuit line.
It should be noted that the contingency analysis also revealed other post-contingency overloaded
elements that were regional problems. These elements were discarded from this analysis since these
© 2014 Electric Reliability Council of Texas, Inc. All rights reserved.
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ERCOT Independent Review of the CenterPoint Katy Area Upgrades Project
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were either not related to the new load addition, were very far from the area of concern, or will be
addressed by subsequent projects.
Figure 2 Contingency Flow on the Brazos – Flewellen 138 kV
The G-1+N-1 and X-1+N-1 analyses showed two different limiting conditions for the study area.
Table 1 shows the results of the reliability analysis for these conditions.
First Contingency
(G-1 or X-1)
1375 MW unit at
STP substation
345/138 kV
transformer in
Zenith
Second Contingency
(N-1)
Monitored Facility
Rate B
(MVA)
Flewellen – Mason Road and
Flewellen – Obrien 138 kV
Brazos – Flewellen 138 kV
280
double circuit
Flewellen – Mason Road and
Brazos – Flewellen 138 kV
Flewellen – Obrien 138 kV
280
double circuit
Table 1 Reliability Analysis for Selected G-1+N-1 and X-1+N-1
© 2014 Electric Reliability Council of Texas, Inc. All rights reserved.
Worst %
Loading
119%
119%
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4. Reliability Analysis of Project Options
Four transmission improvement options were analyzed using PowerWorld Simulator to identify a
reliable and economical solution to serve the Katy area load growth. Detailed cost estimations for all
four projects can be found in Appendix. These four alternatives and the reliability analysis results
are listed below:
Option 1 (Option 2 in CenterPoint Energy’s RPG Submittal)

Convert Katy Substation from a double-tap configuration to a loop configuration on 138 kV
circuit 09, and parallel Flewellen – Franz 138 kV circuit 66 with 138 kV circuit 09 to form
a new 138 kV circuit 09.

Construct two new approximately 6.4 mile 138 kV circuits from Zenith Substation to
two Franz Substation tap points.

Install a second 800 MVA normal/1000 MVA emergency rated 345/138 kV
autotransformer at Zenith Substation.
The total cost estimate for Option 1 is approximately $22.8 million.
N-1 AC contingency analysis showed no overloads with Option 1.
G-1+N-1 AC contingency analysis (loss of a single unit at STP substation 1375 MW) showed no
overloads in the study area.
With the addition of the second autotransformer in Zenith, X-1+N-1 AC contingency analysis (loss
of a single 345/138 kV transformer in Zenith substation) showed no overloads in the study area.
Option 2 (Option 4 in CenterPoint Energy’s RPG Submittal)

Convert Katy Substation from a double-tap configuration to a loop configuration on 138 kV
circuit 09.

Convert Franz Substation from a double-tap configuration to a loop configuration on 138
kV circuit 09.

Construct a new approximately 6.4 mile circuit from Zenith Substation to Franz tap on
double-circuit structures creating a new 138 kV Zenith–Franz–Katy–Flewellen circuit 09.

Install a second 800 MVA normal/1000 MVA emergency rated 345/138 kV
autotransformer at Zenith Substation.

Upgrade 1.6 miles of existing 138 kV circuit from Franz Substation north to the interface
with the new 138 kV circuit to Zenith Substation.
The total cost estimate for Option 2 is approximately $20.4 million.
N-1 AC contingency analysis showed no overloads with Option 2.
G-1+N-1 AC contingency analysis (loss of a single unit at STP substation 1375 MW) showed no
overloads in the study area.
With the addition of the second autotransformer in Zenith, X-1+N-1 AC contingency analysis (loss
of a single 345/138 kV transformer in Zenith substation) showed no overloads in the study area.
© 2014 Electric Reliability Council of Texas, Inc. All rights reserved.
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ERCOT Independent Review of the CenterPoint Katy Area Upgrades Project
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Option 3

Reconductor the existing Brazos
normal/emergency rating.

Install a second 800 MVA normal/1000 MVA emergency rated 345/138 kV
autotransformer at Zenith Substation.
– Flewellen 138 kV line to 441/526 MVA
The cost estimate for reconductoring Brazos – Flewellen is approximately $3.0 million, which can
be derived using ERCOT’s average generic dollar per transmission mile cost.
Option 3 assumes the T H Wharton to Addicks 345 kV line upgrade to an emergency rating 1450
MVAR by 2018. This project was proposed separately in the 2013 Regional Transmission Plan.
N-1 AC contingency analysis showed no overloads with Option 3.
G-1+N-1 AC contingency analysis (loss of a single unit at STP substation 1375 MW) showed no
overloads in the study area.
With the addition of the second autotransformer in Zenith, X-1+N-1 AC contingency analysis (loss
of a single 345/138 kV transformer in Zenith s ubstation) showed no overloads in the study area.
Option 3 is a logical alternative solution since Brazos – Flewellen 138 kV is the overloaded element
found in the base case N-1 contingency analysis. The installation of the second 345/138 kV
transformer in Zenith Substation is needed to meet the X-1+N-1 reliability criteria; without this
autotransformer, the T H Wharton – Willow 138 kV circuit will be overloaded to 108% of its
emergency rating under certain contingencies. Although the Freeman – BETKA – Hockley 138-kV
circuit did not overload by 2018, the post-contingency flows approach 97% of its emergency rating
indicating that it would likely overload in 2019 or 2020 as load growth continues in the area.
Adding this 138 kV line upgrade (approximately 12 miles) will increase the total cost of Option 3 to
approximately $23.9 million, which is higher than Option 2.
ERCOT performed additional analysis to compare the system loss saving for both Option 2 and
Option 3. The results showed that the total system loss saving with Option 2 is 9.18 MW versus
1.05 MW with Option 3.
Option 3 does not address the over 300 MW load loss for the common tower outage of Flewellen –
Katy ckt 66 and Flewellen – Katy ckt 09 which results in the loss of major loads at Katy and Franz.
Option 4

Construct a second circuit, approximately 6.7 mile from Obrien Substation to Flewellen
Substation creating a new 138 kV Obrien–Flewellen circuit, which shall not share a tower
with the existing circuit.

Install a second 800 MVA normal rated / 1000 MVA emergency rated 345/138 kV
autotransformer at Zenith Substation.
The total cost estimate for Option 4 is approximately $26.0 million, based on the CenterPoint
Energy’s estimate that includes new positions at Flewellen and Obrien substations .
Option 4 assumes the T H Wharton to Addicks 345 kV line upgrade to an emergency rating 1450
MVAR by 2018. This project was proposed separately in the 2013 Regional Transmission Plan.
N-1 AC contingency analysis showed no overloads with Option 4.
G-1+N-1 AC contingency analysis (loss of a single unit at STP substation 1375 MW) showed no
overloads in the study area.
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ERCOT Independent Review of the CenterPoint Katy Area Upgrades Project
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With the addition of the second autotransformer in Zenith, X-1+N-1 AC contingency analysis (loss
of a single 345/138 kV transformer in Zenith substation) showed no overloads in the study area.
Option 4 is another logical alternative solution because the limiting contingency is always the
double circuit line coming out of Flewellen. Building a new separate Obrien-Flewellen 138 kV line
will essentially remove the impacts of the double circuit contingency. The installation of the second
345/138 kV transformer in Zenith Substation is needed to meet the X-1+N-1 reliability criteria;
without this autotransformer, the T H Wharton – Willow 138 kV circuit will be overloaded to 108%
of its rate B under certain contingencies .
Option 4 does not address the over 300 MW load loss for the common tower outage of Flewellen –
Katy ckt 66 and Flewellen – Katy ckt 09 which results in the loss of major loads at Katy and Franz.
5. Conclusion
Based on the above analyses, ERCOT recommends Option 2 for the following reasons:

Option 2 has the lowest overall cost estimate.

Option 2 provides all loads in Katy area with an additional source, which is more reliable.
Specifically, the 2018 projected 185 MW load at the Franz substation and the 125 MW load
at the Katy substation will have a new source provided from the Zenith substation with
Option 2. This addition along with converting Franz and Katy into loop stations will solve
the issue of a double circuit tower outage of Flewellen – Katy ckt 66 and Flewellen – Katy
ckt 09 resulting in the loss of these loads at Katy and Franz substations.

Option 2 has lower operational costs in terms of system loss, partially caused by the more
meshed network structure.
In conclusion, the following transmission upgrades studied as Option 2 (Option 4 in the CenterPoint
Energy RPG submittal) constitute the most effective solution to serve the projected load growth in
the Katy area:

Convert Katy Substation from a double-tap configuration to a loop configuration on 138 kV
circuit 09.

Convert Franz Substation from a double-tap configuration to a loop configuration on 138
kV circuit 09.

Construct a new approximately 6.4 mile circuit from Zenith Substation to Franz tap on
double-circuit structures creating a new 138 kV Zenith–Franz–Katy–Flewellen circuit 09.

Install a second 800 MVA normal rated / 1000 MVA emergency rated 345/138 kV
autotransformer at Zenith Substation.

Upgrade 1.6 miles of existing 138 kV circuit from Franz Substation north to the interface
with the new 138 kV circuit to Zenith Substation.
© 2014 Electric Reliability Council of Texas, Inc. All rights reserved.
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ERCOT Independent Review of the CenterPoint Katy Area Upgrades Project
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6. Designated Providers of Transmission Facilities
In accordance with ERCOT Protocol Section 3.11.4.8, ERCOT staff is to designate transmission
providers for projects reviewed in the RPG. These providers can agree to provide or delegate the
new facilities or inform ERCOT if they do not elect to provide them. For the project scope
recommended in this report CenterPoint Energy is the sole designated provider of all transmission
facilities.
© 2014 Electric Reliability Council of Texas, Inc. All rights reserved.
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ERCOT Independent Review of the CenterPoint Katy Area Upgrades Project
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7. Appendix
Estimated Cost
Option 1 (CenterPoint Option 2)
Transmission
Substation
Convert Katy Substation from a double-tap substation to a
loop substation. Upgrade Katy Substation equipment to at
least 440 MVA Rate A and at least 526 MVA Rate B. Keep
existing 14.4 MVAR capacitor bank at Katy Substation.
Loop in 138 kV circuit 09 from Flewellen Substation and
138 kV circuit 09 Franz tap. Parallel 138 kV circuit 66 from
Flewellen to former Franz tap point with 138 kV circuit 09.
Expand 138 kV Zenith Substation to allow for two 138 kV
circuits to be built from Zenith Substation 6.4 miles south to
Franz Substation tap points on 138 kV circuit 66 for one 138
kV circuit and 138 kV circuit 09 for the other 138 kV circuit.
Tap points will be located 1.6 miles from Franz Substation
taps. New configurations will be 138 kV Zenith - Franz tap Katy Loop circuit 09 and 138 kV Zenith - Franz tap Freeman circuit 66. Substation equipment rating at Zenith
and conductor rating of at least 478 MVA Rate A and at least
526 MVA Rate B.
Install a second 800/1000 MVA 345/138 kV autotransformer
at Zenith Substation.
$100,000
$490,000
$8,750,000
$2,800,000
$0
$10,700,000
Total
$22,840,000
Table 2 Option 1 Upgrade Cost Estimates
Estimated Cost
Option 2 (CenterPoint Option 4)
Transmission
Substation
Convert Katy Substation from a double-tap substation to a
loop substation. Upgrade Katy Substation equipment to at
least 440 MVA Rate A and at least 526 MVA Rate B. Keep
existing 14.4 MVAR capacitor bank at Katy Substation.
Loop in 138 kV circuit 09 Flewellen Substation and 138 kV
circuit 09 Franz Substation. Keep one Katy Substation
distribution transformer tapped off 138 kV circuit 66 to form
a new 138 kV Flewellen– Katy tap – Freeman circuit 66.
Convert Franz Substation to a loop substation. Franz
Substation equipment rating of at least 441 MVA Rate A and
at least 526 MVA Rate B.
Expand 138 kV Zenith Substation to allow for one 138 kV
circuit to be built from Zenith Substation 6.4 miles south to
Franz Substation on double-circuit structures. New 138 kV
circuit will interface with former tap off 138 kV circuit 66
approximately 1.6 miles from Franz Substation. New
$200,000
$490,000
$0
$87,000
$6,600,000
$1,690,000
© 2014 Electric Reliability Council of Texas, Inc. All rights reserved.
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ERCOT Independent Review of the CenterPoint Katy Area Upgrades Project
configurations will be 138 kV Flewellen– Katy tap –
Freeman circuit 66 and 138 kV Zenith– Franz– Katy–
Flewellen circuit 09. Substation equipment rating at Zenith
and conductor rating of at least 500 MVA Rate A and at least
600 MVA Rate B. Parallel bundle 4.6 miles 138 kV circuit
66 Franz tap - Franz corner.
Upgrade 1.6 miles from Franz Substation to new 138 kV
circuit from Zenith Substation to a rating of at least 441
MVA Rate A and at least 526 MVA Rate B.
Install a second 800/1000 MVA 345/138 kV autotransformer
at Zenith Substation.
ERCOT Public
$600,000
$0
$0
$10,700,000
Total
$20,367,000
Table 3 Option 2 Upgrade Cost Estimates
Estimated Cost
Option 3
Re-conductor the existing 5.1 miles Brazos – Flewellen 138
kV line to 441/526 MVA normal/emergency rating.
Install a second 800 MVA normal rated / 1000 MVA
emergency rated 345/138 kV autotransformer at Zenith
Substation.
Upgrade the existing 12 mile Freeman – BETKA – Hockley
138 kV line to 287/316 MVA normal/emergency rating.
Transmission
Substation
$3,009,000
$40,000
$0
$10,700,000
$10,200,000
$0
Total
$23,949,000
Table 4 Option 3 Upgrade Cost Estimates
Option 4
Construct a second approximately 6.7 mile circuit from
Obrien Substation to Flewellen Substation creating a new
138 kV Obrien–Flewellen circuit.
Install a second 800 MVA normal rated / 1000 MVA
emergency rated 345/138 kV autotransformer at Zenith
Substation.
Estimated Cost
Transmission
Substation
$7,638,000
$7,700,000
$0
$10,700,000
Total
$26,038,000
Table 5 Option 4 Upgrade Cost Estimates
© 2014 Electric Reliability Council of Texas, Inc. All rights reserved.
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