the influence of the lamar dc tie on the black hills ... · colorado electric 115 kv system –...

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Lamar DC Tie and the BHCE 115 kV System August 22, 2012

1

The Influence of the Lamar DC Tie on the Black Hills

Colorado Electric 115 kV System – Preliminary Study

PREPARED

BY

BLACK HILLS CORPORATION

TRANSMISSION PLANNING

August 22, 2012

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Table of Contents

1. Introduction ............................................................................................................................... 5

2. Study Methodology ................................................................................................................... 7

2.1. Study Criteria ...................................................................................................................... 7

2.2. Study Case Development .................................................................................................... 7

2.3. Scenario Cases Studied ....................................................................................................... 8

3. Steady-State Assessment .......................................................................................................... 9

3.1. Benchmark Case ................................................................................................................. 9

3.2. Second Boone 230-115 kV Transformer Case ................................................................. 15

3.3. New Boone – Nyberg 115 kV Transmission Line Case ................................................... 17

4. Conclusions .............................................................................................................................. 21

Appendix A .................................................................................................................................... A-1 Appendix B .................................................................................................................................... B-1

Appendix C .................................................................................................................................... C-1

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Executive Summary

Background

Transmission Planning identified the need to increase the reliability of the Rocky Ford/La Junta

portion of the Black Hills system and proposed the “Second Boone 230/115 kV Transformer”

project. The benefit of adding a second 230-115 kV transformer at Boone to the reliability of the

Rocky Ford/La Junta portion of the Black Hills system was outlined in the “Second Boone 230/115

kV Transformer Project – Review” study report (April 23, 2012). This study also identified a new

Boone – Nyberg 115 kV transmission line as a viable alternative to the second Boone 230-115 kV

transformer.

This summer the Boone – DOT Tap – Nyberg 115 kV transmission line experienced heavy loading,

especially during periods of high transfers on the Lamar DC Tie and various combinations of

planned transmission line outages on the neighboring 230 kV & 345 kV systems.

The objective of the study was to review the performance of the “Second 230/115 kV Transformer”

project and the “New Boone – Nyberg 115 kV Transmission Line” during periods of high East-

West & West-East flows on the Lamar DC Tie. Also, determine whether the overloads observed on

the Boone – DOT Tap – Nyberg 115 kV were attributable to the generation at Pueblo Airport

Generating Station (PAGS) or the magnitude and direction of the flows on the Lamar DC Tie.

The heavy loading observed on the Boone – DOT Tap – Nyberg 115 kV is exacerbated when the

wind generation at Colorado Green is online, specifically during periods of high East-West flows

on the Lamar DC Tie.

Conclusions

In general the results show that a second 230-115 kV transformer at Boone does little to relieve the

heavy loading observed on the Boone – DOT Tap – Nyberg 115 kV transmission line during

periods of high transfers on the Lamar DC Tie coupled with Colorado Green wind generation. A

series of upgrades are required to create a robust system that meets the required performance

criteria for all but the most extreme scenarios (NERC/WECC Category D).

A new Boone – Nyberg 115 kV transmission line, constructed as a double circuit to

facilitate the upgrade of the existing Boone – DOT Tap – Nyberg 115 kV and to 230 kV

design standard. New 115 kV line positions at Nyberg and Boone. (Q4 2014 - $10M based

upon Baculite Mesa – West Station 115 kV 2011 project).

A second Boone 230-115 kV transformer to relieve the overloads on the existing

transformer during the worst case scenarios. (Q4 2014 - $7.9M TSG&T/Xcel Energy

estimate May 14, 2012).

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Rebuild the Boone 115 kV facility rather than add more elements to the single bus. As

discussed in the “Second Boone 230/115 kV Transformer Project – Review” study report

the new line or the new transformer do not mitigate the impact of Boone 115 kV bus

contingency. (Cost & Schedule to be determined).

All stated costs are preliminary and do not convey any commitment of behalf of the affected

entities.

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1. Introduction







transformer.




Figure 1: Boone 230/115/69 kV Transmission Substation

The objectives of the study were:

To review the performance of the “Second 230/115 kV Transformer” project and the “New

Boone – Nyberg 115 kV Transmission Line” during periods of high East-West & West-East

flows on the Lamar DC Tie.

To determine whether the overloads observed on the Boone – DOT Tap – Nyberg 115 kV

were attributable to the generation at Pueblo Airport Generating Station (PAGS) or the

magnitude and direction of the flows on the Lamar DC Tie.

The heavy loading observed on the Boone – DOT Tap – Nyberg 115 kV was exacerbated when the

wind generation at Colorado Green was online, specifically during periods of high East-West flows


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Figure 2: Expected 2015 Black Hills Colorado Electric Transmission System

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2. Study Methodology

The BHCE transmission system was evaluated with planned system additions for 2015 under peak

summer load levels to identify any deficiencies in system performance. Steady state voltage and

thermal analyses was performed. Additional upgrades were identified and modeled as necessary to

mitigate any reliability criteria violations. A list of prior and forced outages used in the study

process was included in Appendix A.

2.1. Study Criteria

The criteria used in this analysis is consistent with the NERC TPL Reliability Standards, WECC

TPL – (001 thru 004) – WECC – 1 – CR ─ System Performance Criteria. Pre-existing voltage and

thermal loading violations outside the localized study area were ignored during the evaluation.

2.1.1. Steady State Voltage Criteria

Under system intact conditions, steady state bus voltages must remain between 0.95 and 1.05 per

unit. Following a Category B or C contingency, bus voltages must remain between 0.90 and 1.10

per unit.

2.1.2. Steady State Thermal Criteria

All line and transformer loading must be less than 100% of their established continuous rating for

system normal conditions (NERC/WECC Category A). All line and transformer loadings must be

less than 100% of their established continuous or emergency rating under outage conditions

(NERC/WECC Category B and C). BHCE utilizes an allowable overload on transformers of up to

125% of the continuous thermal rating for emergency situations. Normal continuous ratings are

assumed for all non-BHCE facilities.

2.2. Study Case Development

A modified WECC approved 2014 heavy summer case used for the BHCT-G10 Generation LGIR

Study and the Second Boone 230-115 kV Transformer Review Study was used to test the

performance of the 2015 scenario. The case included the following planned system upgrades and

changes:

Pueblo Generation Units 5 & 6 suspend operations 2012

Busch Ranch I Wind Project in-service date 12-31-2012

W.N. Clark Generation Units 1 & 2 retirement 2013

Busch Ranch II Wind Project in-service date 10-01-2014

Pueblo Airport Generating Station Unit 3, 40 MW simple-cycle, natural gas-fired turbine,

preliminary in-service date 2016 (included)¹ BHCE/BHCI FAC-009 Facility Rating Document Revision U (08-10-2012)

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Reader-Rattlesnake Butte 115 kV line – 2012

Greenhorn-Reader 115 kV line upgrade – 2012

Portland – West Station 115 kV #1 line upgrade and #2 new line - 2012

Pueblo-Hyde Park-West Station 115 kV line upgrade – 2013

Reader 115-69 kV transformers T1 & T2 replacement - 2013

Canon City 115 kV Capacitor Bank - 2013

La Junta – Tri-State Interconnect project (2014) o New 115 kV transmission line between La Junta (BHCE) and La Junta (TSG&T) o La Junta (BHCE) 115/69 kV transformer T1, replaced with unit rated 42 MVA o La Junta (BHCE) 115/69 kV transformer T2, new unit rated 42 MVA o La Junta (BHCE)-Rocky Ford 69 kV CT increase rating to conductor limit o Boone-La Junta (BHCE) 115 kV CT increase rating to conductor limit o Boone-Boone Tap 69 kV CT increase rating to conductor limit o Rocky Ford-S. Fowler Tap 69 kV CT increase rating to conductor limit

Overton 115 kV substation and Baculite Mesa-Overton-Northridge 115 kV upgrade –

2015 (project not fully defined so not included)

Colorado Green wind generation at 20 MW

It should be noted that the San Luis Valley-Calumet-Comanche transmission project and the Lamar

Front Range transmission project were not included in the 2015 study cases. A detailed listing of

the case updates is available upon request.

2.3. Scenario Cases Studied

The benchmark study was with all facilities in-service and the output of the Lamar DC Tie set at

200 MW East -West, 100 MW East - West, 100 MW West – East and 200 MW West – East. A set

of contingency studies were then performed under each of the following scenarios:

Benchmark, system prior to any upgrades.

Second Boone 230/115 kV 150 MVA Transformer (planned 2014) in-service

New Boone – Nyberg 115 kV Transmission Line in-service.

1 PAGS Unit #3 was included in the case based on the Baseline Expansion Plan within the 2012 BHCE Electric

Resource Plan. Actual siting of this resource is TBD.

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3. Steady-State Assessment

The BHCE transmission system consists of three distinct regions within the BHCE service

territory. The Cañon City area is located at the western end of the system, and is served via

230/115 kV transformer at West Cañon, the West Cañon-Poncha 115 kV line, and the Portland-

West Station 115 kV lines. The Pueblo area lies in the center of the service territory and consists of

the region surrounding the city of Pueblo, extending eastward to Boone. The Rocky Ford area is

on the east end of the service territory and extends from Boone to La Junta. This study was

intended to illustrate the impact of the Lamar DC Tie upon the BHCE 115 kV System. Specifically

the loading on the Boone-DOT Tap-Nyberg 115 kV line during west to east flows on the tie and

loading West Station-Desert Cove-Fountain Valley-Midway (WAPA) during east to west flows.

The results are described below. All stated costs are preliminary estimates based upon 2012 dollars

and do not convey any commitment of behalf of the affected entities.

3.1. Benchmark Case

3.1.1. Benchmark Results

Figure 3: Benchmark Case with System Intact (All Lines in Service)

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With the system intact all facilities were within their voltage and thermal limits for maximum East-

West & West-East flows at Lamar. It was noted that with 200 MW West-East at Lamar the Boone

– DOT Tap 115 kV line was loaded to 96% of its 100 MVA rating. Also, for 200 MW East-West at

Lamar the West Station-Desert Cove 115 kV line was loaded to 79% of its 80 MVA rating.

Figure 4: Benchmark Case with N-1 Contingency (Boone – Comanche 230 kV) & Lamar DC

Tie (200 MW West – East)

For West-East flows on the Lamar DC Tie, with respect to the Boone – DOT Tap 115 kV line

loading, the generation at the Pueblo Airport Generating Station (PAGS) was 15% effective and the

Lamar DC Tie was 17% effective. For East-West flows on the Lamar, with respect to the West

Station – Desert Cove 115 kV line loading, the generation at PAGS was 11% effective and Lamar

3% effective.

The term “effective” refers to the impact of the source (PAGS or Lamar) has on the loading of the

identified element. So an increase of 10 MW at PAGS produces an increase of 1.1 MW on the

West Station – Desert Cove 115 kV line for East-West flows on the Lamar DC Tie and a Boone –

Comanche 230 kV contingency. A decrease of 10 MW at PAGS produces reduction of 1.1 MW on

the West Station – Desert Cove 115 kV line for East-West flows on the Lamar DC Tie and a Boone

– Comanche 230 kV contingency.

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With a planned/forced outage of the Boone – Comanche 230 kV line and 200 MW flowing West–

East on the Lamar DC Tie as shown in Figure 4, the following was observed:

Boone – DOT Tap 115 kV line 158% of its 100 MVA rating

Nyberg - DOT Tap 115 kV line 136% of its 119 MVA rating

Lamar DC Tie 36% effective and PAGS 14% effective

Figure 5: Benchmark Case with N-1-1 Contingency (Boone – Comanche 230 kV and Boone –

Midway 230 kV) & Lamar DC Tie (200 MW West – East)

With a planned/forced outage of the Boone – Comanche 230 kV and the Boone – Midway (PSCo)

line and 200 MW flowing West–East on the Lamar DC Tie as shown in Figure 5, the following

was observed:



Boone 230-115 kV T1 transformer 123% of its 150 MVA rating

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Lamar DC Tie 119% effective and PAGS 0% effective (MW’s at the Lamar DC Tie produce a

change in MVA on the effected elements)

Also, with a planned/forced outage of the Boone – Comanche 230 kV and the Boone – Midway

(PSCo) line and 200 MW flowing East-West on the Lamar DC Tie, the following was observed:



Figure 6: Benchmark Case with N-1-1 Contingency (Midway – Fuller 230 kV and Midway –

Midway 230 kV) & Lamar DC Tie (200 MW East-West)

With a planned/forced outage of the Midway (PSCo) – Fuller 230 kV and the Midway (WAPA) –

Midway (PSCo) line and 200 MW flowing East-West on the Lamar DC Tie as shown in Figure 6,

the following was observed:

Fountain Valley – Desert Cove 115 kV line 113% of its 115 MVA rating

Fountain Valley – Midway (WAPA) 115 kV line 161% of its 80 MVA rating

Portland – Skala 115 kV line 125% of its 80 MVA rating

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Desert Cove – West Station 115 kV line 192% of its 80 MVA rating

Lamar DC Tie 8-10% effective and PAGS 10-17% effective

Overloads on the Fountain Valley – Midway (WAPA) 115 kV and Desert Cove – West Station 115

kV lines were also observed for West-East flows on the Lamar DC Tie.

A complete list of the results can be found in Appendix C (Table C-1).

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3.1.2. Benchmark Summary

West-East flows at the Lamar DC Tie increase the loading on the Boone – DOT Tap – Nyberg 115

kV line for N-0, N-1 and N-1-1 contingencies. The worst case contingency is a planned/forced

outage of the Boone – Comanche 230 kV and the Boone – Midway (PSCo) 230 kV lines with 200

MW flowing West–East on the Lamar DC Tie. The observed overloads on the Boone – DOT Tap

115 kV line (286%), Nyberg - DOT Tap 115 kV line (244%) and Boone 230-115 kV T1

transformer (123%) were directly attributable to the magnitude and direction of the flows on the

Lamar DC Tie. Although, for the majority of N-1-1 230 kV & 345 kV contingencies studied the

impact of the Lamar DC Tie was only twice that of the generation at PAGs (Lamar DC Tie 35%

effective and PAGS 14% effective).

Table 1: Benchmark Case – Worst Case Results (red) with Prior Outages (yellow)

Boone - Midway (PSCo) 230 kV #1

System Intact BOONE 115.00-DOT_TAP 115.00 #1 94.9

DESRTCOV 115.00-W.STATON 115.00 #1 95.5

Boone - Comanche 230 kV #1 NYBERG 115.00-DOT_TAP 115.00 #1 114.4 143.5 244.2

BOONE 115.00-DOT_TAP 115.00 #1 140.5 166.5 286

BOONE 115.00-BOONE 230.00 #T1 99.7 122.7


Midway (WAPA) - Midway (PSCo) 230 kV #1 DESRTCOV 115.00-W.STATON 115.00 #1 121.4 111.9

Midway (WAPA) - West Canon 230 kV #1 PORTLAND 115.00-SKALA 115.00 #1 124.8 111.6

Boone - Comanche 230 kV #1

System Intact BOONE 115.00-DOT_TAP 115.00 #1 121.6 158

NYBERG 115.00-DOT_TAP 115.00 #1 105.3 136


Midway (WAPA) - West Canon 230 kV #1 PORTLAND 115.00-SKALA 115.00 #1 121.8 109

Midway (PSCo) - Fuller 230 kV #1


Boone - Comanche 230 kV #1 NYBERG 115.00-DOT_TAP 115.00 #1 99.5 129.3

BOONE 115.00-DOT_TAP 115.00 #1 114.5 149.8

Midway (WAPA) - Nixon 115 kV #1 FTN_VLY 115.00-MIDWAYBR 115.00 #1 98.5

DESRTCOV 115.00-W.STATON 115.00 #1 129 123.6 112.3 106.6

MIDWAYBR 115.00-MIDWAYBR 230.00 #1 127.5 123.7 115.8 111.6

Midway (WAPA) - Midway (PSCo) 230 kV #1 FTN_VLY 115.00-DESRTCOV 115.00 #1 113 104.6

FTN_VLY 115.00-MIDWAYBR 115.00 #1 160.5 148.3 122.9 109.9

PORTLAND 115.00-SKALA 115.00 #1 125.1 114.5

DESRTCOV 115.00-W.STATON 115.00 #1 192.1 179.7 153.9 140.8

Midway (WAPA) - West Canon 230 kV #1 PORTLAND 115.00-SKALA 115.00 #1 124 111.5

Contingency Overloaded ElementDC Tie 200

MW E-W

(%)

DC Tie 100

MW E-W

(%)

DC Tie 100

MW W-E

(%)

DC Tie 200

MW W-E

(%)

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East-West flows at the Lamar DC Tie increase the loading on the West Station – Midway (WAPA)

115 kV and Portland – West Canon 115 kV lines for N-0, N-1 and N-1-1 contingencies. The worst

case contingency is a planned/forced outage of the Midway (PSCo) – Fuller 230 kV line and the

Midway (WAPA) – Midway (PSCo) 230 kV bus tie with 200 MW flowing East-West on the

Lamar DC Tie. The observed overloads on the Fountain Valley – Desert Cove 115 kV line (113%),

Fountain Valley – Midway (WAPA) 115 kV line (161%), Portland – Skala 115 kV line (125%)

and Desert Cove – West Station 115 kV line (192%) were more attributable to the generation at

PAGS than the magnitude and direction of the flows on the Lamar DC Tie.

3.2. Second Boone 230-115 kV Transformer Case

3.2.1. Second Boone 230-115 kV Transformer Results

The benefit of adding a second 230-115 kV transformer at Boone to the reliability of the Rocky

Ford/La Junta portion of the Black Hills system was outlined in the “Second Boone 230/115 kV

Transformer Project – Review” study report. Unfortunately it has little impact on reducing the

loading of the Boone - DOT Tap - Nyberg 115 kV line during west to east flows on the tie.

Figure 7: Second Boone 230-115 kV Transformer Case with N-1-1 Contingency (Boone –

Comanche 230 kV and Boone – Midway 230 kV) & Lamar DC Tie (200 MW West – East)

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was observed:



3.2.2. Second Boone 230-115 kV Transformer Summary

The benefit of adding a second 230-115 kV transformer at Boone to the reliability of the Rocky

Ford/La Junta portion of the Black Hills system was outlined in the “Second Boone 230/115 kV

Transformer Project – Review” study report. Unfortunately it has little impact on reducing the

loading of the Boone - DOT Tap - Nyberg 115 kV line during west to east flows at Lamar.

Table 2: Second Boone 230-115 kV Case – Worst Case Results (red) with Prior Outages

(yellow)


System Intact BOONE 115.00-DOT_TAP 115.00 #1

DESRTCOV 115.00-W.STATON 115.00 #1 96


BOONE 115.00-DOT_TAP 115.00 #1 140.7 166.8 284.3

BOONE 115.00-BOONE 230.00 #T1





System Intact BOONE 115.00-DOT_TAP 115.00 #1 125.1 162.1

NYBERG 115.00-DOT_TAP 115.00 #1 108.3 139.5






BOONE 115.00-DOT_TAP 115.00 #1 118.9 155.5




Midway (WAPA) - Midway (PSCo) 230 kV #1 FTN_VLY 115.00-DESRTCOV 115.00 #1 113.3 104.8

FTN_VLY 115.00-MIDWAYBR 115.00 #1 160.9 148.7 123.2 110.2

PORTLAND 115.00-SKALA 115.00 #1 125.4 114.7




MW E-W

(%)

DC Tie 100

MW E-W

(%)

DC Tie 100

MW W-E

(%)

DC Tie 200

MW W-E

(%)

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Although, in some contingencies studied the reduction in impedance at Boone 230 kV actually

increases the overloads on the Boone – DOT Tap – Nyberg 115 kV line. See Table 4.

3.3. New Boone – Nyberg #2 115 kV Transmission Line Case

3.3.1. New Boone – Nyberg #2 115 kV Transmission Line Results

The benefit of adding a new Boone – Nyberg 115 kV transmission line to the reliability of the


kV Transformer Project – Review” study report. It also reduces the loading of the existing Boone -

DOT Tap - Nyberg 115 kV line during west to east flows on the tie. Unfortunately it increases the

loading upon the existing Boone 230-115 kV T1 transformer.

Figure 8: New Boone – Nyberg 115 kV Line Case with N-1-1 Contingency (Boone –

Comanche 230 kV and Boone – Midway 230 kV) & Lamar DC Tie (200 MW West – East)

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was observed:



Boone 230–115 kV T1 transformer 118% of its 150 MVA rating

Table 3: New Boone – Nyberg 115 kV Case – Worst Case Results (red) with Prior Outages

(yellow)




Boone - Comanche 230 kV #1 NYBERG 115.00-DOT_TAP 115.00 #1 112.3

BOONE 115.00-DOT_TAP 115.00 #1 129.3

BOONE 115.00-BOONE 230.00 #T1 100.8 117.7






NYBERG 115.00-DOT_TAP 115.00 #1

BOONE 115.00-BOONE 230.00 #T1 72.3





Boone - Comanche 230 kV #1 NYBERG 115.00-DOT_TAP 115.00 #1

BOONE 115.00-DOT_TAP 115.00 #1


DESRTCOV 115.00-W.STATON 115.00 #1 128.9 123 110.8 104.7



FTN_VLY 115.00-MIDWAYBR 115.00 #1 160.8 148.2 122.1 108.7

PORTLAND 115.00-SKALA 115.00 #1 125.3 114.4




MW E-W

(%)

DC Tie 100

MW E-W

(%)

DC Tie 100

MW W-E

(%)

DC Tie 200

MW W-E

(%)

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3.3.2. New Boone – Nyberg 115 kV Transmission Line Summary

The benefit of adding a new Boone – Nyberg 115 kV transmission line to the reliability of the


kV Transformer Project – Review” study report. It also reduces, but does not eliminate the loading

of the Boone - DOT Tap - Nyberg 115 kV line during west to east flows on the tie. Also, it

increases the loading upon the Boone 230-115 kV T1 transformer during high west to east flows.

Table 4: BHCE 115 kV System – Worst Case Results (red) with Prior Outages (yellow)

Reader - Airport Memorial 115 kV #1


West Station - Bacul i te Mesa 115 kV #1 & #2 NYBERG 115.00-DOT_TAP 115.00 #1 144.9 153.4 170.6 178.9

BACULITE MSA115.00-NTHRIDGE 115.00 #1 164.9 156.8 140.6 132.2

BOONE 115.00-DOT_TAP 115.00 #1 168.4 178.5 199 206

MIDWAYPS 115.00-NTHRIDGE 115.00 #1 160.9 151.5 132.6 122.8

Portland - West Station 115 kV #1 & #2 DESRTCOV 115.00-W.STATON 115.00 #1 108.3 103.3

W.CANON 115.00-W CANON 230.00 #T1 124.3 122 117.3 115

BOONE 115.00-DOT_TAP 115.00 #1 109.1


Midway - West Canon 230 kV #1 PORTLAND 115.00-SKALA 115.00 #1 122.8 110.1



West Station - Bacul i te Mesa 115 kV #1 & #2 NYBERG 115.00-DOT_TAP 115.00 #1 154.1 162.4 178.1 185.9

BACULITE MSA115.00-NTHRIDGE 115.00 #1 156.6 149.1 133.8 126

BOONE 115.00-DOT_TAP 115.00 #1 179.4 189.2 207.9 217


Portland - West Station 115 kV #1 & #2 DESRTCOV 115.00-W.STATON 115.00 #1 107.9 103

W.CANON 115.00-W CANON 230.00 #T1 124.3 122 117.3 115

BOONE 115.00-DOT_TAP 115.00 #1 98.1 113





West Station - Bacul i te Mesa 115 kV #1 & #2 NYBERG 115.00-DOT_TAP 115.00 #1

BACULITE MSA115.00-NTHRIDGE 115.00 #1 152.5 143.6 125.7 116.8

BOONE 115.00-DOT_TAP 115.00 #1 103.2 108.8


BOONE 115.00-BOONE 230.00 #T1 109.9 105.2

Portland - West Station 115 kV #1 & #2 DESRTCOV 115.00-W.STATON 115.00 #1 107.2 101.6

W.CANON 115.00-W CANON 230.00 #T1 124.4 122 117.3 115.1

BOONE 115.00-DOT_TAP 115.00 #1



BOONE - NYBERG 115 PROJECT

BOONE 230-115 T2 PROJECT

NO SYSTEM UPGRADES


MW E-W

(%)

DC Tie 100

MW E-W

(%)

DC Tie 100

MW W-E

(%)

DC Tie 200

MW W-E

(%)

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With respect to contingencies on the BHCE 115 kV System around the Pueblo Airport Generating

Station (PAGS), the worst case scenario is a planned/forced outage of the West Station – Baculite

Mesa 115 kV Double Circuit and the Reader – Airport Memorial 115 kV line. It is interesting to

note that while the addition of the new Boone – Nyberg 115 kV line reduces the impact upon the

existing Boone – DOT Tap 115 kV line during west to east flows, it increases the loading upon the

Boone 230-115 kV T1 transformer during high east to west flows. The observed overloads on the

Boone – DOT Tap 115 kV line (206%), Nyberg - DOT Tap 115 kV line (179%) were mainly due

to the generation at PAGS (52%) rather than the magnitude and direction of the flows on the Lamar

DC Tie (8%). See Table 4: BHCE 115 kV – Worst Case Results.

Table 5: New Boone – Nyberg 115 kV Case – Colorado Green Wind Sensitivity (red) with

Prior Outages (yellow)



DESRTCOV 115.00-W.STATON 115.00 #1 96.1 100.6

Boone - Comanche 230 kV #1 NYBERG 115.00-DOT_TAP 115.00 #1 110.3

BOONE 115.00-DOT_TAP 115.00 #1 135.2

BOONE 115.00-BOONE 230.00 #T1 100.8 177.9


LAMAR_CO 115.00-LAMAR_CO 230.00 #T1 113.3





NYBERG 115.00-DOT_TAP 115.00 #1

BOONE 115.00-BOONE 230.00 #T1





Boone - Comanche 230 kV #1 NYBERG 115.00-DOT_TAP 115.00 #1

BOONE 115.00-DOT_TAP 115.00 #1

Midway (WAPA) - Nixon 115 kV #1 FTN_VLY 115.00-MIDWAYBR 115.00 #1 98.4 100.6


MIDWAYBR 115.00-MIDWAYBR 230.00 #1 127.5 131.3


FTN_VLY 115.00-MIDWAYBR 115.00 #1 160.8 168.9

PORTLAND 115.00-SKALA 115.00 #1 125.3 132.5



Contingency Overloaded ElementDC Tie 200 MW E-W

Co Green Wind 20 MW

(%)

DC Tie 200 MW E-W Co

Green Wind 160 MW

(%)

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21


wind generation at Colorado Green is included, specifically during periods of high East-West flows

on the Lamar DC Tie. See Table 5: New Boone – Nyberg 115 kV Case – Colorado Green Wind

Sensitivity.

4. Conclusions







transformer.




The objective of the study was to review the performance of the “Second 230/115 kV Transformer”

project and the “New Boone – Nyberg 115 kV Transmission Line” during periods of high East-

West & West-East flows on the Lamar DC Tie. Also, determine whether the overloads observed on

the Boone – DOT Tap – Nyberg 115 kV were attributable to the generation at Pueblo Airport

Generating Station (PAGS) or the magnitude and direction of the flows on the Lamar DC Tie.


wind generation at Colorado Green is online, specifically during periods of high East-West flows


In general the results show that a second 230-115 kV transformer at Boone does little to relieve the

heavy loading observed on the Boone – DOT Tap – Nyberg 115 kV transmission line during

periods of high transfers on the Lamar DC Tie and the Colorado Green wind generation online. A

new Boone – Nyberg 115 kV transmission line meets the required performance in all but the worst

case scenarios. A series of upgrades are required to create a robust system that meets the required

performance criteria for all but the most extreme scenarios (NERC/WECC Category D).

A new Boone – Nyberg 115 kV transmission line, constructed as a double circuit to

facilitate the upgrade of the existing Boone – DOT Tap – Nyberg 115 kV and to 230 kV

design standard. New 115 kV line positions at Nyberg and Boone. (Q4 2014 - $10M based

upon Baculite Mesa – West Station 115 kV 2011 project).

_________________________________________________________________________________________________________________


22

A second Boone 230-115 kV transformer to relieve the overloads on the existing

transformer during the worst case scenarios. (Q4 2014 - $7.9M TSG&T/Xcel Energy

estimate May 14, 2012).

Rebuild the Boone 115 kV facility rather than add more elements to the single bus. As

discussed in the “Second Boone 230/115 kV Transformer Project – Review” study report

the new line or the new transformer do not mitigate the impact of Boone 115 kV bus

contingency. (Cost & Schedule to be determined).

All stated costs are preliminary and do not convey any commitment of behalf of the affected

entities.

.

_________________________________________________________________________________________________________________


A-1

Appendix A

Steady State

Prior and Forced Outage Lists

_________________________________________________________________________________________________________________


A-2

_________________________________________________________________________________________________________________


A-3

_________________________________________________________________________________________________________________


A-4

_________________________________________________________________________________________________________________


B-1

Appendix B

Load and Resource

Assumptions

_________________________________________________________________________________________________________________


B-2

Table B1: Black Hills Colorado Load and Resource Assumptions

SCENARIO CA

NO

N_55

70083

CA

NO

N_59

70084

E_C

AN

ON

70160

PP

_M

INE

70306

PU

B_D

SL

S

70334

PU

EB

PL

NT

G1

70337

PU

EB

PL

NT

G2

70337

R.F

.DS

LS

70344

AP

T_D

SL

S

71001

BA

C_M

SA

GE

N1

71001

BA

C_M

SA

GE

N2

71002

BA

C_M

SA

GE

N3

71003

BA

C_M

SA

GE

N3

71003

BA

C_M

SA

GE

N3

71003

BA

C_M

SA

GE

N4

71004

BA

C_M

SA

GE

N4

71004

BA

C_M

SA

GE

N4

71004

BA

C_M

SA

GE

N5

71005

BU

SC

HR

WT

G1

71009

BU

SC

HR

WT

G2

71012

CO

MA

NC

HE

C1

70119

CO

MA

NC

HE

C2

70120

CO

MA

NC

HE

C3

70777

CO

GR

EE

N W

1

70701

CO

GR

EE

N W

2

70702

2015 Heavy Summer 0 0 0 0 10 20 7 10 10 90 90 40 40 20 40 40 20 40 29 29 355 360 804 10 10

Total BHCE Generation 535 MW

Total BHCE Load 466 MW

Area Import -69 MW

_________________________________________________________________________________________________________________


C-1

Appendix C

Comparison of the Study Results

_________________________________________________________________________________________________________________


C-2

Table C1: Benchmark Study Case Results (red) with Prior Outages (yellow)

Daniels Park - Comanche 345 kV #1




BOONE 115.00-DOT_TAP 115.00 #1 128.4 163.2

Daniels Park - Comanche 345 kV #2 COMANCHE 230.00-WALSENBG 230.00 #1 100

FTN_VLY 115.00-MIDWAYBR 115.00 #1 120.8 114.1 100.1

PALMER 115.00-MONUMENT 115.00 #1 111.3 104.7

PORTLAND 115.00-SKALA 115.00 #1 130.9 121.7 102.3


KETTLECK 115.00-FLYHORSE 115.00 #1 103.7 98.4

MIDWAYPS 115.00-MIDWAYPS 230.00 #T1 104.2 98

Midway (WAPA) - Midway (PSCo) 230 kV #1 FTN_VLY 115.00-MIDWAYBR 115.00 #1 109.1


PORTLAND 115.00-SKALA 115.00 #1 110.6

Midway - West Canon 230 kV #1 PORTLAND 115.00-SKALA 115.00 #1 139 125.8





BOONE 115.00-DOT_TAP 115.00 #1 140.5 166.5 286

BOONE 115.00-BOONE 230.00 #T1 99.7 122.7





System Intact BOONE 115.00-DOT_TAP 115.00 #1 121.6 158

NYBERG 115.00-DOT_TAP 115.00 #1 105.3 136



Comanche - Midway (PSCo) 230 kV #1



BOONE 115.00-DOT_TAP 115.00 #1 128 162.9



DC Tie 200

MW E-W

(%)


MW E-W

(%)

DC Tie 100

MW W-E

(%)

DC Tie 200

MW W-E

(%)

_________________________________________________________________________________________________________________


C-3


…..continued



BOONE 115.00-DOT_TAP 115.00 #1 114.5 149.8


DESRTCOV 115.00-W.STATON 115.00 #1 129 123.6 112.3 106.6


Midway (WAPA) - Midway (PSCo) 230 kV #1 FTN_VLY 115.00-DESRTCOV 115.00 #1 113 104.6

FTN_VLY 115.00-MIDWAYBR 115.00 #1 160.5 148.3 122.9 109.9

PORTLAND 115.00-SKALA 115.00 #1 125.1 114.5



Midway (WAPA) - Nixon 230 kV #1



BOONE 115.00-DOT_TAP 115.00 #1 114.6 149.9

Midway (PSCo) - Ful ler 230 kV #1 AS ABOVE - - - -

Midway (WAPA) - Lincoln 230 kV #1


Boone - Comanche 230 kV #1 NYBERG 115.00-DOT_TAP 115.00 #1 104 133.8

BOONE 115.00-DOT_TAP 115.00 #1 119.8 155.2

Midway (WAPA) - Midway (PSCo) 230 kV #1 DESRTCOV 115.00-W.STATON 115.00 #1 125.2 118.6 104.8


Midway (WAPA) - West Canon 230 kV #1

System Intact PORTLAND 115.00-SKALA 115.00 #1 121.8 109.2


BOONE 115.00-DOT_TAP 115.00 #1 113.5 149.6

Portland - West Station 115 kV #2 PORTLAND 115.00-W.STATON 115.00 #1 115.5 107.9

West Canon - Ponchar (WAPA) 230 kV #1



BOONE 115.00-DOT_TAP 115.00 #1 116.5 151.9




MW E-W

(%)

DC Tie 100

MW E-W

(%)

DC Tie 100

MW W-E

(%)

DC Tie 200

MW W-E

(%)

_________________________________________________________________________________________________________________


C-4


…..continued


Boone - Comanche 230 kV #1 NYBERG 115.00-DOT_TAP 115.00 #1 102 131.6

BOONE 115.00-DOT_TAP 115.00 #1 117.4 152.6


Midway (WAPA) - Nixon 115 kV #1



BOONE 115.00-DOT_TAP 115.00 #1 117.3 152.4

Midway (WAPA) - Midway (PSCo) 230 kV #1 DESRTCOV 115.00-W.STATON 115.00 #1 104.1



MW E-W

(%)

DC Tie 100

MW E-W

(%)

DC Tie 100

MW W-E

(%)

DC Tie 200

MW W-E

(%)

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