3. 5015-21-3104 DMAFB Substation - 100% Elec Calc Package.pdf

Project Name:

Proj. Number: Date: 5-Oct-22

Location: Designed By: S.Santilian

Proj. Phase: Checked By: M.Griffith

Temp. Ambient (aT) = 30 °F Cable Tension = 17,700 lb Ice Thickness (i1, i2)= 0 inches Tension Initial (Ti) = 4750 lb Wind Pressure (wP) = 9 lb/ft² Tension Final (Tf) = 4425 lb

NESC Constant (K)= 0.05 lb/ft Span1 (S1) = 150 ft Cable Linear Weight (cW)= 0.969 lb/ft Span2 (S2) = 200 ft

Cable Diameter (D)= 1.17 inches Span3 (S3) = 250 ft Span3 (S4) = 300 ft

Ice Weight (iW) = 1.24 * i * (D + i) = 0.00 lb/ft

Wind Load (wL) = wP * (D + 2*i) / 12 = 0.878 lb/ft

Resultant Weight (rW) = SqRt( (cW + iW)² + wL² ) + K = 1.357 lb/ft rW (w/ Ice) = rW (w/o Ice)

Span1 Sag Initial (Di) = S1² * rW / (8 * Ti) 0.804 ft for no ice location

Span1 Sag Final (Df) = S1² * rW / (8 * Tf) 0.863 ft

Span2 Sag Initial (Di) = S2² * rW / (8 * Ti) 1.429 ft

Span2 Sag Final (Df) = S2² * rW / (8 * Tf) 1.534 ft

Span3 Sag Initial (Di) = S3² * rW / (8 * Ti) 2.232 ft

Span3 Sag Final (Df) = S3² * rW / (8 * Tf) 2.396 ft

Span4 Sag Initial (Di) = S4² * rW / (8 * Ti) 3.215 ft

Span4 Sag Final (Df) = S4² * rW / (8 * Tf) 3.451 ft

Tucson, AZ is a "Light Loading Zone" per NESC.

Davis-Monthan AFB: Substation Switching and Distribution

Design Base: Southwire AAC "Bluebell" 1033.5 kcmil

OVERHEAD CABLE

5015213104

Tucson, AZ

30%

DM Calcs 10/27/2022

Part 2: Safety Rules for Overhead Lines

Copyright © 2016 IEEE. All rights reserved.

The Warm Island Loading District includes American Samoa, Guam, Hawaii, Puerto Rico, Virgin Islands, and other islands located from 0 to 25 degrees latitude, north or south.

Figure 250-1—General loading map of United States with respect to loading of overhead lines

F-250-1 F-250-1

Copyright The Institute of Electrical and Electronics Engineers, Inc.

Provided by IHS Markit under license with IEEE Licensee=AMECFW5 /5947185179, User=Gill, Dwayne

Not for Resale, 12/12/2017 08:45:32 MSTNo reproduction or networking permitted without license from IHS stephen.santilian Text Box Page From:

IEEE C2-2017 National Electric Safety Code (NESC) stephen.santilian Arrow stephen.santilian Text Box Tucson, AZ

Power System Report

Document Title: 251230 Davis-Monthan – Power System Report Revision: 0 Date on Document: 15 June 2022 Page: 15 after fault clearing timess from TEP are available.

For the outgoing feeders, where protective device settings can be set by DMAFB, the clearing time was assumed to be 0.2 seconds or less as reasonable time for instantaneous operation and clearing the fault.

The arc flash results for the main 13.8 kV bus at the DMAFB Substation (or the new DMAFB Switching Station for Option 3) are summarized in Table 6-1 and in Appendix B.

Table 6-1: Arc Flash Incident Energy

Option Cell

B us

B ol te d

Fa ul t (k

A)

B us

A rc in g

Fa ul t

Tr ip

/D ela y T im e (S ec

In cid en t E ne rg y (c al/ cm

2 )

En er gy Le ve l

A rc

Fl as h B ou nd ar y

(f t)

W or kin g

Di sta nc e

(I nc he s)

1 Incoming 7.67 7.48 2 34.80 E 8.08 18 Outgoing 7.67 7.48 0.2 3.48 B 2.55 18

2 Incoming 6.03 5.90 2 26.93 E 7.10 18 Outgoing 6.03 5.90 0.2 2.69 B 2.25 18

3 Incoming 15.88 15.29 2 75.38 F 11.89 18 Outgoing 15.88 15.29 0.2 7.54 C 3.76 18

Although the above results must be re-evaluated in the detailed design stage, based on relay settings at TEP substation, these preliminary findings show that the incident energy at the incoming side of the new proposed switchgear at the switching station exceed PPE Category 4 (40 cal/cm2) in Option 3. Any work at the incoming side of the switchgear should not be permitted with the equipment energized. The new switchgear should be specified as Arc Resistant type, with breakers fully withdrawable and accessories to allow for remote operation of the draw-out mechanism to minimize exposure to the effects of a fault events involving the incoming section or main bus of the switchgear.

The incident energy at the feeder cells of the new switchgear is below 8 cal/cm2, consistent with an arc flash PPE Category 2 (8 cal/cm2) which requires workers to wear cotton underwear plus flame resistant shirt and pants as PPE.

To reduce the arc flash incident energy in Option 3, the bus coupler should be open in the normal operating condition.

7 Summary For Options 1 and 2, VRs combined with fixed capacitor banks are recommended. VRs combined

USSS718871

Line

USSS718871

Line

Date on Document: 15 June 2022 Page: 16 with fixed capacitor banks are recommended to provide effective voltage control and reactive compensation, under peak demand load condition, estimated demand during winter and summer, both during normal operating conditions as well as in the event of a single incident that takes one 13.8 kV circuits out of service.

For Option 3, the use of fixed capacitor banks provides adequate voltage control and reactive power compensation. The proximity of the new switching station to the TEP substation, compared with Options 1 and 2, alleviates the voltage drop along the new 13.8 kV circuits, discarding the need for additional voltage regulation provided by the VRs.

The short circuit current levels calculated are within the range of what is commonly available from equipment manufacturers. The short circuit capacity of new equipment will be specified to withstand the calculated short circuit current levels under ultimate short circuit conditions. The short circuit current capacity of existing equipment connected to the new power distribution system will need to be verified against the calculated ultimate short circuit fault levels.

The arc flash incident energy was calculated based on assumed protection relay settings and clearing times. While this method does not exactly calculate incident energy levels and arc flash protection boundaries at the buses under consideration, it does allow for identification of areas with high energy levels. This will guide the following arc flash analysis efforts to conduct a hazard/risk assessment, determine level of PPE required, and identify opportunities to reduce relay settings that could help to minimize arc flash levels.

Based on the calculations completed, the incident energy at the incoming side of the new proposed switchgear at the switching station can exceed PPE Category 4 (40 cal/cm2). Any work at the incoming side of the switchgear should not be permitted with the equipment energized.

The new switchgear should be specified as Arc Resistant type, with breakers fully withdrawable and accessories to allow for remote operation of the draw-out mechanism to minimize exposure to the effects of a fault events involving the incoming section or main bus of the switchgear.

The incident energy at the feeder cells of the new switchgear is below 8 cal/cm2, consistent with an arc flash PPE Category 2 (8 cal/cm2) which requires workers to wear cotton underwear plus flame resistant shirt and pants as PPE.

DMAFB Switching Station and Distribution RAMP

Document Title: 251230 Davis-Monthan – RAMP Document Revision: 0 Date on Document: 15 June 2022 Page: 10

RUS Bulletin 1724E-200 RUS Bulletin 1728F-806 RUS bulletin 1728F-700 RUS bulletin 1724F-151 IEEE Std. 141-1993 (R1999) IEEE Std. 738-2006 Avian Protection Plan (APP) Guideline Specification and Drawings for Underground Electric Distribution, USDA

3 Overhead Conductor and Cable Selection Based on the 24 MVA peak demand load, the required current carrying capacity of the overhead conductors and underground cables at 13.8 kV is 1004 A.

I = 1000 x P / (√3 x VL-L) Where:

I = current in Amps P = power in MVA VL-L = line-line voltage in kV

3.1 Overhead Conductor

Based on IEEE Std. 738-2006 - Standard for Calculating the Current-Temperature of Bare Overhead Conductors, a single 1033.5 kcmil, 'Bluebell’, All Aluminum Conductor (AAC) per phase was selected for the overhead line sections. Table 3-1 (from Southwire) shows the typical ratings for a range of AAC conductors.

Date on Document: 15 June 2022 Page: 11

Table 3-1: Southwire AAC Overhead Conductor Ratings

Code Word

Size (kcmil)

Stranding Diameter (ins.) Cross- Sectional

Area (Sq. ins.)

Weight Per ft.

(lbs.)

Rated Strength

(lbs.)

Resistance

OHMS/1000

ft.

Allowable Ampacity`

(Amps) No. of Wires

Class Individual Wires

Complete Cable

DC @

20°C

AC @

75°C

Meadowsweet 600 37 AA .1273 .891 .4709 562 10700 .0228 .0355 738 Orchid 636.0 37 AA, A .1311 .918 .4995 596 11400 .0272 .0335 765

Heuchera 650 37 AA .1325 .928 .5102 609 11600 .0266 .0328 775 Verbena 700 37 AA .1375 .963 .5494 656 12500 .0247 .0305 812

Flag 700 61 A .1071 .964 .5495 656 12900 .0247 .0305 812 Violet 715.5 37 AA .1391 .973 .5623 671 12800 .0242 .0299 823

Nasturtium 715.5 61 AA .1083 .975 .5619 671 13100 .0242 .0299 823 Petunia 750.0 37 AA .1424 .997 .5893 703 13100 .0230 .0286 847 Cattail 750 61 AA .1109 .998 .5892 703 13500 .0230 .0286 847

Arbutus 795 37 AA .1466 1.026 .6245 745 13900 .0217 .0270 878 Lilac 795.0 61 A .1142 1.027 .6248 745 14300 .0217 .0270 879

Cockscomb 900 37 AA .156 1.092 .7072 844 15400 .0192 .0239 948 Snapdragon 900 61 AA .1215 1.093 .7072 844 15900 .0192 .0239 948

Magnolia 954.0 37 AA .1606 1.124 .7495 894 16400 .0181 .0226 982 Goldenrod 954.0 61 A .1251 1.125 .7498 894 16900 .0181 .0226 983 Hawkweed 1000 37 AA .1644 1.151 .7854 937 17200 .0173 .0216 1010 Camellia 1000 61 AA .128 1.152 .7849 937 17700 .0713 .0216 1011

Bluebell 1033.5 37 AA .1671 1.17 .8114 969 17700 .0167 .0210 1031

Larkspur 1033.5 61 AA .1302 1.171 .8122 969 18300 .0167 .0210 1032 Marigold 1113.0 61 AA, A .1351 1.216 .8744 1043 19700 .0155 .0195 1079 Hawthorn 1192.5 61 AA, A .1398 1.258 .9363 1118 21100 .0145 .0183 1124 Narcissus 1272.0 61 AA, A .1444 1.3 .999 1192 22000 .0136 .0173 1169

Columbine 1351.5 61 AA, A .1488 1.34 1.0608 1267 23400 .0128 .0163 1212

3.2 Cable Section

Based on the required current carrying capacity of 1004 A, two 750 kcmil copper (Cu) cables per phase were selected for the cable sections. Cu cables have been chosen over aluminum (Al) due to their smaller diameter, high ampacity in duct, availability of standard terminations, and easy installation in duct banks and pull boxes.

Date on Document: 15 June 2022 Page: 12

Each 750 kcmil cable has an ampacity of 610 A at 105°C in duct. Error! Reference source not found. (from Prysmian) shows the typical ratings for a range of 15 kV copper cables. Maximum cable ampacity will be evaluated through thermal calculations during detailed design.

Table 3-2: Prysmian 15 kV Copper Cable Ratings

Conductor

Insulation Thickness

(mils)

Conductor Diameter

(in)

Insulation Diameter

(in)

Insulation Shield

Diameter (in)

Jacket Diameter

(in)

Cable Weight (lbs/kft)

Minimum Bending

Radius (in)

† Ampacity (Amps)

105°C In Duct

105°C In Air

2 AWG 220 0.266 0.74 0.80 0.96 590 12 165 215

1 AWG 220 0.299 0.78 0.83 1.00 696 12 185 250

1/0 AWG 220 0.341 0.82 0.88 1.04 762 13 215 290

2/0 AWG 220 0.376 0.85 0.91 1.07 863 13 245 335

3/0 AWG 220 0.423 0.90 0.96 1.12 1036 14 275 385

4/0 AWG 220 0.479 0.96 1.02 1.17 1161 15 315 445

250 MCM 220 0.522 1.01 1.06 1.22 1314 15 345 495

350 MCM 220 0.622 1.11 1.16 1.32 1676 16 415 610

500 MCM 220 0.742 1.23 1.28 1.44 2204 18 500 765

750 MCM 220 0.917 1.41 1.47 1.63 3110 20 610 990

1000 MCMU 220 1.071 1.57 1.62 1.84 4056 23 690 1185

† In Duct per 2017 NEC Table 310.60(C)(77): Three single conductor cables in plastic duct, direct-buried, 105°C conductor temperature, 20°C ambient temperature, earth RHO of 90°C-cm/Watt, and 100% load factor, and shields short-circuited.

4 Overhead Line Structures Single circuit and double structures have been considered.

The structure configurations will need to be evaluated by conducting a detailed pole loading analysis during detailed design to confirm the structural capacity to support the selected overhead conductors and to ensure compliance with applicable standards such as required span lengths, guying/anchoring, etc.

4.1.1 Double-Circuit Structures

A double-circuit wood pole structure following RUS standard VD2.91 is proposed. This pole configuration is shown in Figure 4-1. In this structure, the double crossarms with V-brace and double posts help distribute the conductor load and provide additional support. Subject to a pole loading analysis, the top wood crossarms may be replaced by steel to sustain the vertical loads.

Date on Document: 15 June 2022 Page: 7

1 References The short circuit, protection settings, and arc flash evaluation follows the guidelines of the following standards:

IEEE Std. 1584 - IEEE Guide for Arc Flash Calculations IEEE Std. 242 - IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems

2 Methodology For this study, the power system was modelled from the Point of Interconnection (POI) at the TEP Patriot Substation to the existing switchgear at the DMAFB Substation.

The TEP system at the POI was modeled as a Thevenin equivalent. Refer to later sections of this report for the equivalent sequence impedances used in the model.

The new 13.8 kV overhead and underground circuits were modeled based on the anticipated configuration of the circuits. Refer to the RAMP Document (251230-0000-DH00-RPT-0001) for more details.

The loads fed from the DMAFB Substation were modeled as a 13.8 kV lumped load.

Specific input data and assumptions are covered in later sections of this report.

3 Design Inputs

3.1 System Information

The nominal voltage at the POI is 13.8 kV. The initial and ultimate fault levels at the POI (provided by DMAFB) are included in Table 3-1.

Table 3-1: Initial and Ultimate Fault Levels at the POI

Short circuit Level

Initial Ultimate

(MVA) (A) (MVA) (A)

Three Phase 423 17,697 463.92 19,409 Single Phase 146.25 18,356 154.64 19,409

3.2 Modeling

3.2.1 General

ETAP® software version 19.0.1.08619 was used to perform the power system analysis.

The models were built up based on the route options for interconnecting the TEP Patriot Substation to the DMAFB loads as shown in Figure 1-1, Figure 1-2, and Figure 1-3 and summarized

Date on Document: 15 June 2022 Page: 8 in Table 3-2.

Table 3-2: Route Options

Option Source Routing

Destination Red (4,485 ft)

Magenta (1,615 ft)

Green (5,320 ft)

Blue (6,400 ft)

1 TEP Patriot Substation

OH Line (4,485 ft)

OH Line (1,615 ft)

OH Line (5,320 ft)

OH Line (6,400 ft)

DMAFB Substation

2 TEP Patriot Substation

UG Cable (4,485 ft)

UG Cable (1,615 ft)

UG Cable (5,320 ft)

OH Line (6,400 ft)

DMAFB Substation

3 TEP Patriot Substation

UG Cable (4,835 ft)

New DMAFB Switching Station

UG Cable (6,400 ft)

DMAFB Loads

The DMAFB loads were modelled as a lump load connected at 13.8 kV, with an assumed power factor of 0.85 lagging at peak design load of 24 MVA.

3.2.2 Source Modeling

The Thevenin equivalent impedances at the POI (provided by DMAFB) are shown in Table 3-3.

Table 3-3: Thevenin Impedance at the TEP Patriot Substation

Sequence Impedance (Ohms)

% Impedance (pu, 100 MVA base)

Positive 0.01958+j0.45696 0.92277+j21.5357 Negative 0.0196+j0.45714 0.92277+j21.5357

Zero 0.03635+j0.40674 1.92012+j21.4852

3.2.3 Overhead Line Modeling

The overhead lines were modeled with conductor 1033.5 kcmil, All Aluminum Conductor (AAC), code name “Bluebell”, with a horizontal triangular configuration (approximately 3.33 ft horizontal distance between the conductors – see Figure 3-1), with an ampacity of 1031 A.

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Date on Document: 15 June 2022 Page: 9

Figure 3-1: Overhead Line Configuration

The impedance of the overhead line is calculated by ETAP® and summarized in Table 3-4.

Table 3-4: Impedance of 13.8 kV Overhead Line

Sequence Resistance (Ω/mile)

Reactance (Ω/mile)

Susceptance (Ω-mile)

Positive 0.0936 0.58442 7.49823 Negative 0.0936 0.58442 7.49823 Zero 0.36995 2.92205 2.51026

Date on Document: 15 June 2022 Page: 10

3.2.4 Underground Cable Modeling

The underground sections were modeled with two 15 kV, 133% Copper, 750 kcmil cables per phase. The cable specification from Prysmian Cables is listed in Table 3-5.

Table 3-5: Prysmian 15 kV Cable Specification

Conductor Size

(kcmil)

Insulation Thickness

(mils)

Conductor Diameter

(in)

Insulation Diameter

(in)

Insulation Shield

Diameter (in)

Jacket Diameter

(in)

Cable Weight (lbs/kft)

Min.

Bending Radius

(in)

Ampacity @105°C In Duct (Amps)

750 220 0.917 1.41 1.47 1.63 3110 20 610

The ampacity shown is based on “In Duct” per 2017 NEC Table 310.60(C)(77): Three single conductor cables in plastic duct, direct-buried, 105°C conductor temperature, 20°C ambient temperature, earth RHO of 90°C-cm/Watt, 100% load factor, and shields short-circuited, 4 Load Flow

4.1 Load Cases

The design peak demand load as specified by DMAFB is 24 MVA at 13.8 kV.

According to the energy consumption recorded from January 2020 to January 2021, provided by DMAFB, the summer and winter power demand was approximately 47% and 44% of the peak load, respectively. Based on this trend and future load growth, the expected summer and winter loads are assumed to be 60% and 55% of peak load, respectively.

The worse case scenario for all options is to supply DMAFB Switching Station through the one circuit at peak demand load.

Based on this, the following load flow cases were developed.

Table 4-1: Load Cases

Load Case Number of Circuits in Service

DMFAB Load

(MVA)

Peak 1 1 24 Peak 2 2 24 Summer 2 14.4 Winter 2 13.2

Date on Document: 15 June 2022 Page: 11

4.2 Load Flow Criteria

The following criteria were considered as the minimum for acceptable load flow performance:

1. The maximum voltage drop from the POI to the step-down transformers at the various DMAFB load centers should not exceed 5%.

On this basis, 3% voltage drop was allocated from the POI to the 13.8 kV main bus in the existing DMAFB Substation switchgear (or the new DMAFB Switching Station for Option 3).

2. The power factor (pf) at TEP Patriot Substation should be 0.95 lagging or better.

4.3 Load Flow Results

The load flow results for the various route options and load cases are shown in Table 4-2 below.

In this table, green color indicates acceptable values, orange color indicates marginally acceptable, and red color indicates values not meeting the requirement.

Table 4-2: Load Flow Results

Option Load Case DMAFB Main Bus

Voltage (pu)

TEP Patriot Sub.

Power Factor

Peak 1 0.902 80.18 Peak 2 0.949 82.99 Summer 0.969 84.21 Winter 0.972 84.36

Peak 1 0.926 81.83 Peak 2 0.971 84.6 Summer 0.983 85.2 Winter 0.984 85.24

Peak 1 0.982 85.2 Peak 2 0.991 85.6 Summer 0.995 85.76 Winter 0.995 85.78

Based on these results, reactive compensation is required to compensate the load power factor and provide voltage control at the 13.8 kV main bus.

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Date on Document: 15 June 2022 Page: 12

4.4 Reactive Compensation

The various alternatives for reactive power compensation are described in Table 4-3.

Table 4-3: Reactive Compensation Alternatives

Designation Description 12 Mvar auto 12 Mvar auto-switching capacitor banks (2 x 4 Mvar + 2 x 2 Mvar) 12 Mvar fixed 12 Mvar fixed capacitor banks (2 x 6 Mvar) 12 Mvar fixed, VR 12 Mvar fixed capacitor banks (2 x 6 Mvar) and series automatic voltage regulator 6 Mvar fixed 6 Mvar fixed capacitor bank (2 x 3 Mvar)

The load flow results for the various route options and load cases along with the different reactive compensation alternatives are shown in Table 4-4 below. In this table, green color indicates acceptable values and orange color indicates marginally acceptable.

Table 4-4: Load Flow Results with Reactive Compensation

Option Load Case

Reactive Compensation

DMAFB Main Bus Voltage

(pu)

TEP Patriot Sub.

Power Factor

Peak 1 12 Mvar auto 0.966 99.05 Peak 2 12 Mvar auto 0.985 99.70 Summer 12 Mvar auto (1) 0.987 98.92 Winter 12 Mvar auto (1) 0.99 99.50

Peak 1 12 Mvar fixed 0.966 99.05 Peak 2 12 Mvar fixed 0.985 99.70 Summer 12 Mvar fixed (2) 0.987 98.92 Winter 12 Mvar fixed (2) 0.99 99.50

Peak 1 12 Mvar fixed, VR 0.998 97.70 Peak 2 12 Mvar fixed, VR 0.998 99.40 Summer 12 Mvar fixed, VR (2) 1.000 98.60 Winter 12 Mvar fixed, VR (2) 0.999 99.29

Peak 1 12 Mvar auto 0.975 99.50 Peak 2 12 Mvar auto 0.990 99.90 Summer 12 Mvar auto (1) 0.992 99.20 Winter 12 Mvar auto (1) 0.993 99.70

Peak 1 12 Mvar fixed 0.975 99.50 Peak 2 12 Mvar fixed 0.990 99.90 Summer 12 Mvar fixed (2) 0.992 99.20 Winter 12 Mvar fixed (2) 0.993 99.70

Peak 1 12 Mvar fixed, VR 0.997 98.50 Peak 2 12 Mvar fixed, VR 0.998 99.70 Summer 12 Mvar fixed, VR (2) 1.000 98.90 Winter 12 Mvar fixed, VR (2) 0.997 99.50 stephen.santilian Line stephen.santilian Line stephen.santilian Highlight

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Date on Document: 15 June 2022 Page: 13

Option Load Case

Reactive Compensation

DMAFB Main Bus Voltage

(pu)

TEP Patriot Sub.

Power Factor

Peak 1 6 Mvar fixed 0.988 95.17 Peak 2 6 Mvar fixed 0.994 95.43 Summer 6 Mvar fixed 0.997 99.35 Winter 6 Mvar fixed 0.998 99.76

Notes:

(1) Auto switched capacitor bank set to maximum 6 Mvar.

(2) One 6 Mvar capacitor bank switched out.

A large active load (kW) combined with large reactive flows (Mvar) will cause substantial losses along the new 13.8 kV circuits, low power factor at the POI, and low voltage profile at the DMAFB end of the new circuits. As power factor decreases, total circuit current increases, causing further voltage drop. To improve these conditions, several reactive compensation alternatives were evaluated as presented in Table 4-3.

The results of the load flow calculations summarized in Table 4-4 show that all the compensation alternatives provide power factor and voltage control within acceptable limits, based on the load flow criteria. The voltage drop for the peak load condition with only one 13.8 kV primary circuit in service is slightly above the 3% criteria (highlighted in orange in Table 4-4) for two cases but is considered acceptable given the extreme concurrence of peak load during a contingency condition.

The following discusses the reactive compensation alternatives considered:

Auto-Switching Capacitor Banks Switching operation in multi-step automatic capacitor banks could cause switching transients when a capacitor bank is energized adjacent to a capacitor bank that is already energized (back-to-back switching transients). Each switching event can result in power quality problems for nearby loads. Harmonic resonance conditions could also be excited. Tuned filters, pre-insertion of resistance or inductance, and zero-voltage crossing control are some of the mitigation actions that could be implemented to improve the performance of these switching operations.

Fixed Capacitor Banks Reactive compensation can also be attained with the use of fixed capacitor banks. Fixed capacitor banks offer the greatest economy and simplicity compared with multi-step automatic switched capacitor banks. The choice between fixed and switched capacitors mostly depends on variability in loading throughout the day. Fixed capacitors are more suitable when the facility operates around the clock at a constant load demand. If the load is rather variable, switched capacitor banks become more practical as they bring only as much reactive power (Mvar) as needed at any given time.

Date on Document: 15 June 2022 Page: 14

Voltage Regulators with Fixed Capacitor Banks The automatic load tap-changer of the voltage regulator (VR) can maintain the bus voltage within desired limits, compensating the voltage drop caused along the 13.8 kV circuits. The capacitor banks provide the reactive power required by the load, reducing the current draw from the 13.8 kV power supply, reducing power losses, and therefore assisting the voltage regulation.

From the alternatives considered, the combination of VRs and fixed capacitor banks is recommended for Options 1 and 2. VRs provide effective voltage control at the DMAFB switchgear main bus, compensating the voltage drop along the 13.8 kV circuits through the on-load tap changer, while the capacitor banks provide reactive compensation for the load, reducing the current draw from the 13.8 kV main circuits. It should be noted that fixed capacitor banks have been considered under the assumption of a load profile consistent with a constant load demand behavior. This profile behavior will be reviewed during the detailed design of the project to confirm this choice. It is important to mention that the capacitor banks are to be connected between the VRs and the load. In this case, the voltage level or compensation settings at the VRs may require tuning to avoid toggling between the VRs and the voltage correction that could be produced by the capacitor bank.

For Option 3, two 3 Mvar fixed capacitor bank provides sufficient reactive power compensation and voltage control.

5 Short Circuit The short circuit levels calculated at the 13.8 kV main bus in the existing DMAFB Substation switchgear (or the new DMAFB Switching Station for Option 3) for ½ cycle are summarized in Table 5-1 and In Appendix A.

For the short circuit calculations, it was assumed that the fault current contribution from the existing DMAFB motors or other connected loads was negligible.

Table 5-1: Short Circuit Levels

Option Initial Short Circuit (kA) Ultimate Short Circuit (kA) Single Phase 3 Phase Single Phase 3 Phase

1 4.20 7.34 4.26 7.67 2 7.85 5.83 8.10 6.03 3 13.10 14.52 13.77 15.88

6 Arc Flash An Arc Flash assessment was performed based on IEEE Std. 1584 with the bus fault current calculation for 3-Phase symmetrical ½ cycle for the ultimate short circuit fault level case.

For incoming feeders which be protected by backup protection at the TEP Patriot Substation, two seconds for fault clearing time was considered. It is important to note that this is a conservative assumption that can yield a high incident energy. This assessment is to be reviewed

Date on Document: 15 June 2022 Page: 15 after fault clearing timess from TEP are available.

For the outgoing feeders, where protective device settings can be set by DMAFB, the clearing time was assumed to be 0.2 seconds or less as reasonable time for instantaneous operation and clearing the fault.

The arc flash results for the main 13.8 kV bus at the DMAFB Substation (or the new DMAFB Switching Station for Option 3) are summarized in Table 6-1 and in Appendix B.

Table 6-1: Arc Flash Incident Energy

Option Cell

B us

B ol te d

Fa ul t

B us

A rc in g

Fa ul t

Tr ip

/D ela y T im e (S ec

In cid en t E ne rg y (c al/ cm

2 )

En er gy Le ve l

A rc

Fl as h B ou nd ar y

(f t)

W or kin g

Di sta nc e

(I nc he s)

1 Incoming 7.67 7.48 2 34.80 E 8.08 18 Outgoing 7.67 7.48 0.2 3.48 B 2.55 18

2 Incoming 6.03 5.90 2 26.93 E 7.10 18 Outgoing 6.03 5.90 0.2 2.69 B 2.25 18

3 Incoming 15.88 15.29 2 75.38 F 11.89 18 Outgoing 15.88 15.29 0.2 7.54 C 3.76 18

Although the above results must be re-evaluated in the detailed design stage, based on relay settings at TEP substation, these preliminary findings show that the incident energy at the incoming side of the new proposed switchgear at the switching station exceed PPE Category 4 (40 cal/cm2) in Option 3. Any work at the incoming side of the switchgear should not be permitted with the equipment energized. The new switchgear should be specified as Arc Resistant type, with breakers fully withdrawable and accessories to allow for remote operation of the draw-out mechanism to minimize exposure to the effects of a fault events involving the incoming section or main bus of the switchgear.

The incident energy at the feeder cells of the new switchgear is below 8 cal/cm2, consistent with an arc flash PPE Category 2 (8 cal/cm2) which requires workers to wear cotton underwear plus flame resistant shirt and pants as PPE.

To reduce the arc flash incident energy in Option 3, the bus coupler should be open in the normal operating condition.

7 Summary For Options 1 and 2, VRs combined with fixed capacitor banks are recommended. VRs combined