8. DMAFB Electrical Dist - Design Analysis - 100 percent.pdf

Design Analysis for

DMAFB Substation Switching and Distribution

FBNV190002

Prepared for:

United States Air Force

Davis-Monthan Air Force Base

Tucson, Arizona

Prepared by:

Infrastructure Engineering Solutions JV

964 5th Ave, Ste 214

San Diego, CA 92101-6102

Project No.: 251230

Issued for Construction

19 January 2024

DMAFB Substation Switching and Distribution Design Analysis 19 January 2024

Page i

TABLE OF CONTENTS

Page

1.0 GENERAL DESCRIPTION

1.1 Introduction

1.2 System Design Requirements

1.3 Project Scope

2.0 PROJECT REQUIREMENTS AND PROVISIONS

2.1 Design Criteria

2.1.1 Standards

2.1.2 References

2.1.3 Assumptions

2.1.4 Overhead Conductors

2.1.5 Ground Clearances

2.1.6 Vertical Separations

2.1.7 Horizontal Separations

2.1.8 Steel Pole Design Parameters

2.1.9 Cross Arm Design Parameters

2.1.10 Steel Pole Setting

2.1.11 Sag and Tension Calculations

2.2 Underground Electrical Design

2.2.1 Conduit Fill Calculations

2.2.2 Cable Pulling Tension Calculations

2.2.3 Distribution Structure Mounted Switches

2.2.4 Duct Banks

2.2.5 General

2.2.6 Utilities

2.3 Outline of Technical Specifications

3.0 OPERATION AND MAINTENANCE (O&M) PROVISIONS

3.1 Substation and E-House Lighting

Page ii

APPENDICES

Appendix A - Calculations

Appendix B - Catalog Cut Sheets

Page iii

ACRONYMS AND ABBREVIATIONS

A Amps (Amperes) ACSR Aluminum Conductor Steel Reinforced AHJ Authority Having Jurisdiction ASCE American Society of Civil Engineers AWG American Wire Gauge CAD Computer-Aided Drafting CMU Concrete Masonry Unit DE Dead-End DoD Department of Defense DOR Designer of Record EPD Environmental Protection Division EPR Ethylene Propylene Rubber HDPE High Density Polyethylene IEEE Institute of Electrical and Electronics Engineers kA Kilo-Amps kcmil One Thousand Circular Mils kV Kilo-Volts LED Light-Emitting Diode LOTO Lock-out, tag-out LV Low Voltage (less than 1000 volts) MV Medium Voltage (1000 volts to 69 kilovolts) NEC National Electrical Code NESC National Electrical Safety Code NFPA National Fire Prevention Association NPDES National Pollutant Discharge Elimination System O&M Operation and Maintenance OSHA Occupational Safety and Health Administration PMS Pad Mounted Switch PPE Personal Protective Equipment PVC Polyvinyl Chloride TOC Table of Contents UFC United Facilities Criteria UFGS Unified Facilities Guide Specifications UL Underwriters Laboratories USACE U.S. Army Corps of Engineers

Design Analysis 19 January, 2024

1.0 General Description

1.1 Introduction

Infrastructure Engineering Solutions JV (the JV) has been contracted by the United States Air Force

(USAF) to provide design services for a new switchgear E-House and two new 13.8kV overhead primary power distribution circuits to Davis-Monthan Air Force Base (DMAFB) in Tucson, Arizona.

The JV will design the new electrical distribution overhead feeders to the DMAFB substation and the layout for the new electrical equipment E-House as described in the Statement of Work and

Requirements document. The JV is the Designer of Record (DOR) for this project.

New Power Distribution Equipment

The DMAFB substation design includes the design of new overhead redundant 13.8kV electric lines, tie-in to the Tucson Electric Power (TEP) Patriot substation, new redundant 13.8kV underground feeders, retrofitting the existing 15kV DMAFB Switchgear with new incoming switch compartments, and a new elevated switchgear E-House complete with all station service devices. The substation new work shall include: new E-House, new distribution structures for incoming overhead lines, new steel poles, new underground cables to and from the new 15 kV switchgear, new reactive power compensation equipment, additional new grounding, and lightning protection mast with static wires.

The new E-House will contain all new: 15kV switchgear, station service batteries, DC charger, eyewash, 125VDC panelboard, HVAC, lighting, 208Y/120VAC panelboard, general use receptacles, and an exterior mounted station service transformer (SST).

Protection & Controls for New Switchgear

Metering, protection, and controls shall be provided for the new 15kV switchgear. Contractor purchase of new MV switchgear shall include a “Relay Programming and Startup” package provided by the relay/switchgear manufacturer.

Demolition

No demolition work shall be included in this project. The existing 46kV/13.8kV equipment shall be tagged-out and locked-out in preparation for the base outage. After a successful transfer of base power to the TEP Patriot Substation, only the existing primary 15kV feeders to the DMAFB

Switchgear shall be disconnected, coiled away, and capped.

1.2 System Design Requirements

The existing base-wide electrical distribution system utilizes a 13.8 kV, 3-phase, 3-wire, grounded system configuration. The system consists of both overhead and underground distribution. The existing available fault current of 19.4 kA was calculated in a base-wide Electrical Distribution System

Engineering Study by the JV in June 2022. Circuit protection for all system components related to the scope of work described herein will be provided as required.

The existing distribution loads will not be impacted by this project since there will not be loads added to the system.

Electrical outages and cutovers will be coordinated between the General Contractor and DMAFB

Engineering to minimize interruptions and allow for continued base operations. Site work will be coordinated with the base Utilities Department to minimize the potential for subsurface interference.

All reasonable effort will be made when routing the new underground duct banks to avoid conflicts with existing subsurface utilities.

1.3 Project Scope

The project scope begins at the two new TEP Patriot Substation distribution switches for DMAFB.

TEP has designed the feeds to these 13.8kV switches for service to the DMAFB Substation and the switches will be treated as “existing” for ready connection to serve DMAFB Substation. The overhead circuits will include the installation of a series of new steel power poles and two steel distribution structures between TEP and the DMAFB substation as shown on the design drawings.

Existing 46kV Power Feeders

Deenergize and lock out the two existing 46kV motor operated switches feeding DMAFB Substation.

Each switch cuts off one 46kV line and are located outside of DMAFB Substation.

Existing 15kV DMAFB Switchgear

Disconnect the feeders serving the existing DMAFB 15kV switchgear at the primary of the lineup.

Refeed the existing DMAFB 15kV switchgear from the new DMAFB Substation switchgear E-House.

Wiring and routing shall be installed as described in the design drawings.

Capacitor Bank

Two new 6-MVAR capacitor banks shall be installed at the substation for power factor correction.

These banks will be installed next to the new DMAFB Substation E-House and fed with underground cables as shown on the design drawings.

Distribution Structure with Switches

A new steel structure with overhead line switches will be installed within the substation for connection to the new 13.8kV Circuit #1. An underground primary duct bank with 5-inch conduits will be installed from the Structure to the new E-House.

A new steel Structure with overhead line switches will be installed within the substation for connection to the new 13.8kV Circuit #2. An underground primary duct bank with 5-inch conduits will be installed from the Structure to the new E-House.

Substation Grounding and Slab

A new grounding grid shall be installed for connection to new electrical equipment and E-House. The new ground grid shall be tied into the existing substation grounding system as shown on the electrical design drawings.

New concrete slabs shall be poured in place for E-House and equipment foundations as shown on the structural design drawings.

Electrical Equipment Locations

The proposed locations for the substation E-House, structures, capacitor banks, duct banks, and steel poles are shown on the design drawings. New equipment locations have been selected to best align with existing/new devices and incoming overhead feeders.

2.0 Project Requirements and Provisions

2.1 Design Criteria

2.1.1 Standards

The following Standards and Publications were referenced in the design of this project:

A. Air Force instructions, manuals, and Engineering Technical Letters

B. American Society of Civil Engineers (ASCE) / Structural Engineering Institute (SEI) o ASCE/SEI 48: Design of Steel Transmission Pole Structures o ASCE/SEI 72: Design of Steel Lighting Support Pole Structures

C. American Society for Testing and Materials International o ASTM A871: Standard Specification for High-Strength Low-Alloy Structural Steel Plate with Atmospheric Corrosion Resistance

D. Arizona Building Code (ABC) – Adopts 2018 International Building Code (IBC) with state and local amendments, as applicable

E. Institute of Electrical and Electronics Engineers (IEEE) o IEEE C2: National Electrical Safety Code (NESC) – Latest Edition o IEEE 399: Recommended Practice for Power System Analysis – Latest Edition

F. National Fire Protection Association (NFPA) o NFPA 70: National Electrical Code (NEC) – Latest Edition o NFPA 70E: Standard for Electrical Safety in the Workplace – Latest Edition

G. Unified Facilities Criteria (UFC) o UFC 3-550-01: Exterior Electrical Power Distribution o UFC 3-501-01: Electrical Engineering o UFC 4-010-01: DoD Minimum Antiterrorism Standards for Buildings

H. Occupational Safety and Health Administration (OSHA) o 29 CFR 1910.147: The Control of Hazardous Energy (Lockout/Tagout)

I. Air Force Manual (AFMAN) o AFMAN 91-201: Explosives Safety Standards

J. United States Department of Agriculture (USDA) o USDA RUS Bulletin 1724E-214: Standard Class Steel Transmission Poles

2.1.2 References

The following references were provided by USAF for use in the design of this project:

A. Statement of Work for FBNV190002, Repair-Construct Primary Electric Distribution for Energy

Resiliency, Basewide, dated November 19, 2020.

B. 251230 Davis-Monthan, Power System Report by Infrastructure Engineering Solutions JV, June 15, 2022.

2.1.3 Assumptions

A. All documentation provided by DMAFB engineering are assumed to be accurate. Any discrepancies identified will be brought to the attention of the project team.

2.1.4 Overhead Conductors

Overhead conductors shall be bare All Aluminum Conductors (AAC).

Conductor ampacity for both Circuit #1 and Circuit #2 shall be no less than 1004A. This is based on a

24MVA peak demand load at 13.8kV/3P. The basis of design for overhead medium voltage distribution in these areas will be Bluebell 1033.5 kcmil, All Aluminum Conductor (AAC), 37 strand cable, with allowable ampacity of 1031A.

2.1.5 Ground Clearances

The vertical design clearances to ground will adhere to the NESC Section 232, Table 232-1. The minimum basis of design for 13.8kV phase conductor clearance will be 18.5 feet. The minimum basis of design for 750 volts or less phase conductor clearance will be 16.0 feet.

2.1.6 Vertical Separations

Vertical separation requirements will adhere to the NESC. The basis of design for vertical separation between 13.8kV phase conductors will be 18 inches.

2.1.7 Horizontal Separations

Horizontal separation requirements will adhere to the NESC. The basis of design for horizontal separation between phase conductors circuit will be 14 inches.

2.1.8 Steel Pole Design Parameters

Steel pole design will be developed per ASCE/SEI 48-11 requirements for steel transmission poles based on the various power cable, span, and directional configurations present in the transmission line. Steel transmission poles are anticipated to be 12-sided poles of a class to be determined to minimize the number of unique poles required.

Design loading values will be developed in conjunction with a steel transmission pole manufacturer to match recommendations to available and pre-qualified steel pole stock. Valmont poles were used as a basis of design to develop loading specifications.

2.1.9 Cross Arm Design Parameters

Cross arm design will be based on equipment located on the poles and the direction in which the conductors are routed.

2.1.10 Steel Pole Setting

Steel poles will be supported either by self-embedment in soil/backfill or via a drilled concrete pier or caisson foundation. Foundation type will be determined by Geotechnical analysis of soil capacities and design pole forces at soil levels. Attempts to reduce the number of unique foundations required for the project will be made.

2.1.11 Sag and Tension Calculations

Sag and tension calculations will be performed to determine span lengths. The initial loaded conductor tension will be limited to a maximum of 50% of the conductor rated breaking strength. The rated strength of the basis of design Bluebell 1033.5 kcmil cable is 17,700 lbs.; therefore, the initial tension will be limited to 8850 lbs. The final tension will be limited to 25% of the conductor rated breaking strength; therefore, the final tension will be limited to 4425 lbs.

Per UFC 3-550-01, the maximum design tensions for any conductor shall be 4,750 pounds.

Clearance values shall be based on a maximum temperature of 194°F (90°C) for aluminum/aluminum alloy phase conductors. Calculations will be provided in accordance with NESC and UFC 3-550-01.

Tension T = s2W / 8d

W = Resultant Weight (lbs/ft)= SqRt( (cW + iW)² + wL² ) + K where s = span (ft), d = sag (ft)

Resultant weight (W) is calculated based on ice thickness, wind pressure, and NESC constants.

Ambient Temperature, aT = 30ºC

Ice Thickness, i1 = 0.00 in

Ice Thickness, i2 = 0.00 in

Wind Pressure, wP = 9.00 lb/ft2

NESC Constant, k1 = 0.05 lb/ft

The design basis Bluebell 1033.5 kcmil cable has the following properties:

Cable Weight = 0.969 lb/ft

Cable Diameter = 1.17 in

The resultant weight for the basis of design initial and final conditions will be approximately 1.357 lbs/ft. This initial and final equivalence comes from the NESC “Light Loading Zone” classification with no ice component for Tucson, AZ.

Initial Tension = 4,750 lb

Initial Sag, 150 ft span = 0.804 ft

Initial Sag, 200 ft span = 1.429 ft

Initial Sag, 250 ft span = 2.232 ft

Initial Sag, 300 ft span = 3.215 ft

Final Tension = 4,425 lb

Final Sag, 150 ft span = 0.863 ft

Final Sag, 200 ft span = 1.534 ft

Final Sag, 250 ft span = 2.396 ft

Final Sag, 300 ft span = 3.451 ft

2.2 Underground Electrical Design

Underground medium voltage (MV) cables will be single conductor, copper, 15 kV, EPR, 133% insulation, MV-105, tape shield, jacketed. The basis of design cable will be Southwire Simpull Spec

46302. The 750 kcmil basis of design cable has a listed allowable ampacity of 610A per set installed in underground electrical ducts per the NEC.

Grounding cables will be 4/0 AWG, 600-volt insulation.

2.3.1 Cable Ampacity Calculations

A. Cable Derating

The basis of design underground primary cable listed above has a listed ‘in duct’ rating of 610A. The ampacity includes derating per NEC and IEEE 399 requirements when placed in an underground duct bank. The ambient soil temperature is assumed to be 20ºC. The standard thermal resistivity for the soil is RHO = 90ºC-cm/W; at this value, the adjustment factor for thermal conductivity of the underground cable is unity (1.0).

A minimum of two spare conduits will be provided in each duct bank for future use. A derating factor is required for grouping conductors in the duct bank. Per IEEE 399, if the spare conduit were to be utilized, the 750 kcmil conductors would be derated by a factor of 0.885 to 540A. Two sets of derated parallel 750 kcmil conductors can still carry the full loads of 1004A for each circuit.

To account for the extreme heat of Tucson, which will decrease the cable’s ability to carry current, and the final equipment temperature ratings, 3 parallel sets of 750 kcmil insulated conductors will be installed per phase.

2.2.1 Conduit Fill Calculations

The duct bank conduit will be sized for a maximum of 40% fill with the basis of design cables, in accordance with NEC requirements. Per NEC Chapter 9, Table 4, 40% of the cross-sectional area of

5-inch Schedule 40 PVC and HDPE conduit is 7.904 in2.

The basis of design 750 kcmil cable has an outer jacket diameter of 1.63 inches, which results in a cross-sectional area of 2.09 in2. The basis of design grounding cable has an outside diameter of

0.568 inches, which results in a cross-sectional area of 0.253 in2. The total cross-sectional area of all conductors will be 6.51 in2. This satisfies the 40% fill criteria of the 5” conduits.

Jam ratio of the conductors is calculated as 1.05 times the ratio of the inside diameter of the conduit over the outside diameter of the cable. Jamming only occurs within a jam ratio of 2.7 to 3.1. The outside diameter of the 750 kcmil cable is 1.63 inches. The nominal inside diameter of 5” PVC/HDPE conduit is 5.016 inches. Therefore, the jam ratio is calculated as 3.23, which produces an improbable chance of cable jamming in the conduit. However, conduit shall be installed with long sweeping bends to facilitate cable pulling and maintain the minimum bending radius.

2.2.2 Cable Pulling Tension Calculations

The listed maximum pulling tension of the basis of design 750 kcmil cable is 6000 lbs. This is a product of the allowable stress of the copper (0.008 lbs/cmil) and the size of the copper (750000 mils).

The actual straight pulling tension during installation is a product of the length of the pull, the weight of the cable, a weight correction factor, and the coefficient of friction. For the basis of design 750 kcmil cable, the weight will be 3.2 lbs/ft for a single conductor and 9.6 lbs/ft for triplexed cable. The weight correction factor of triplexed cable is 1.17. The coefficient of friction will be 0.5 for lubricated cable.

The pulling tension can therefore be calculated as 5.62 lbs/ft times the length of the pull. There are no straight pulls anticipated to exceed 600 feet. The expected pulling tension for a 600-foot pull would be

3372 lbs., which is well below the maximum allowable tension.

Conduit bends are expected to be installed in long sweeps, which will result in minimal impact on the pulling tension.

2.2.3 Distribution Structure Mounted Switches

Medium voltage overhead service switches will be rated for 1200 amperes continuous.

2.2.4 Duct Banks

Duct banks will feature either four or six conduits (schedule 40 PVC) encased in concrete for all underground routes. A minimum of two spare conduits will be provided in each duct bank for future use.

Concrete for encasement of underground ducts must be 3000 psi minimum 28-day compressive strength. Concrete associated with electrical work other than the encasement of underground ducts must be 4000 psi minimum 28-day compressive strength unless otherwise noted on the drawings.

2.2.5 General

The structural engineering design for this project is limited to design details for concrete pavement repairs due to the installation of underground duct banks.

2.2.6 Utilities

All underground utilities within the DMAFB substation shall be located prior to start of construction.

2.3 Outline of Technical Specifications

Division 1 – General Requirements

01 45 35 Special Inspections

Division 03 – Concrete

03 30 00 Cast-in-Place Concrete

Division 26 – Electrical

26 05 00.00 40 Common Work Results for Electrical 26 35 33.00 40 Power Factor Correction Equipment

Division 31 - Earthworks

33 63 26 Drilled Caissons

Division 33 - Utilities

33 71 01.00 40 Overhead Transmission and Distribution 33 71 02 Underground Electrical Distribution

3.0 Operation and Maintenance (O&M) Provisions

3.1 Substation and E-House Lighting

Store LED lights in a clean, dry place until ready for installation. Remove all packing materials prior to installation. Install lights in accordance with manufacturer’s instructions and NEC requirements.

Disconnect power prior to performing maintenance and allow drivers a minimum of one minute to discharge after disconnecting power. Follow manufacturer’s instructions when opening and closing access door for maintenance. Ensure proper alignment and seal after door is closed. The photocell receptacle may be adjusted by loosening the mounting screws, rotating the photocell to the desired position, and re-tightening the mounting screws.

Appendix A - Calculations

Sag Calculations

Guy Tension Calculations

Cable Pull Calculations

Appendix B - Catalog Cut Sheets

For

Major Electrical Equipment