8. DMAFB Electrical Dist - Design Analysis - 100 percent - REV 1.pdf

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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

Final Issue 21 March 2024

Mar/26/2024

DMAFB Substation Switching and Distribution Design Analysis 21 March 2024

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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

2.2 Overhead Line Electrical Design

2.2.1 Overhead Conductors

2.2.2 Ground Clearances

2.2.3 Vertical Separations

2.2.4 Horizontal Separations

2.2.5 Steel Pole Design Parameters

2.2.6 Cross Arm Design Parameters

2.2.7 Steel Pole Setting

2.2.8 Sag and Tension Calculations

2.3 Underground Electrical Design

2.3.1 Underground Conductors

2.3.2 Conduit Fill Calculations

2.3.3 Cable Pulling Tension Calculations

2.3.4 H-frame Mounted Switches

2.3.5 Duct Banks

2.3.6 General

2.3.7 Landscape

2.3.8 Utilities

2.4 Structural Design Criteria

2.4.1 General Structural Criteria

2.4.2 Steel Pole Foundations

2.4.3 Foundation Design Calculations

2.4.4 Guy Wire Design

2.5 Outline of Technical Specifications

3.0 OPERATION AND MAINTENANCE (O&M) PROVISIONS

3.1 Substation and E-House Lighting

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APPENDICES

Appendix A - Calculations

Appendix B - Catalog Cut Sheets

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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

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 (2) 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 13.8kV, 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 (2) 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 (2) 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 (2) existing 46kV motor operated switches feeding DMAFB Substation. Each switch cuts off one 46kV line and is 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 (2) 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.

ION Power Meters

ION power meters installed in the new vertical sections of the DMAFB SWITCHING STATION “MV- SWGR-DM2" shall be directly connected to the existing AMRS system on COIN for AFCEC monitoring via ethernet (all wireless capability is prohibited; communication protocols not used shall be disabled). This requires verification of existing fiber connectivity to AFNET (in the existing blockhouse) and connecting the new meters to a COIN enabled port on a new AFNET managed switch.

New equipment and related HMI graphics work shall conform with UFC 4-010-06-2016. The installing contractor shall submit a DMAFB FRCS Change Request Form with the equipment submittals providing details of the equipment and changes and/or additions to the existing systems. The Change Request shall be approved by the 355 CES ISO prior to the proposed equipment's approval.

New meters shall meet AFCEC meter requirements/approved model, and the contractor shall include a Risk Management Framework (RMF) for review with the meter submittals.

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.

B. The DOR is responsible for determining pole spacing and quantity required for new installation.

2.2 Overhead Line Electrical Design

2.2.1 Overhead Conductors

Overhead conductors shall be bare All Aluminum Conductor (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.

2.2.2 Ground Clearances

The vertical design clearances to ground will adhere to the NESC Section 232, Table 232-1. The minimum basis of design 13.8kV phase conductor clearance will be 18.5 feet. The minimum basis of design 750 volts or less phase conductor clearance will be 16.0 feet. The minimum basis of design for neutral conductors will be 15.5 feet.

2.2.3 Vertical Separations

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

2.2.4 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.

2.2.5 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 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.

2.2.6 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.

2.2.7 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.

2.2.8 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 8,850 lbs. The final tension will be limited to 25% of the conductor rated breaking strength; therefore, the final tension will be limited to 4,425 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

2.3 Underground Electrical Design

2.3.1 Underground Conductors

Underground medium voltage (MV) cables will be single conductor, copper, 15kV, 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).

At least two (2) 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 (2) 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.

2.3.2 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.

The 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.

2.3.3 Cable Pulling Tension Calculations

2.3.4.1 750 kcmil Cable

The listed maximum pulling tension of the basis of design 750kcmil 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 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.

2.3.4 H-frame Mounted Switches

Medium voltage H-frame mounted overhead service switches will be 1200 ampere continuous.

2.3.5 Duct Banks

Duct banks will feature either four (4) or six (6) conduits (schedule 40 PVC) encased in concrete for all underground routes. At least two (2) spare conduits will be provided in each duct bank for future use.

Concrete for encasement of underground ducts must be 3,000 psi minimum 28-day compressive strength. Concrete associated with electrical work other than the encasement of underground ducts must be 4,000 psi minimum 28-day compressive strength unless otherwise noted on the drawings.

2.3.6 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.

2.3.7 Landscape

Landscape design is limited to sodding and restoring areas affected by the electrical work.

2.3.8 Utilities

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

2.4 Structural Design Criteria

2.4.1 General Structural Criteria

The new transmission and distribution infrastructure in this project, as well as the new substation equipment, is intended to provide all required power to Davis-Monthan Air Force Base. As the base would necessarily be considered an essential facility to remain operational in the event of an extreme loading event, the substation and the associated foundations for the new transmission system will be considered as Risk Category IV per ASCE/SEI 7-16. Based on the seismic and wind loading parameters of the ASCE 7 Hazard Tool, wind loading controls for all components. For Risk Category IV structures, the relevant wind design parameters are:

Ultimate design wind speed, Vult = 115 mph Surface Roughness D, for conservative design Exposure Category D, for conservative design

2.4.2 Steel Pole Foundations

Steel poles will be supported either by self-embedment in soil/backfill or via a drilled concrete caisson foundation. For the conditions where the final pole size, arm configuration, and line connection locations are not known, the foundations will be selected based on assumptions as follows:

For poles with lines that are within 5° of tangent, we have assumed that the resulting ground-level forces will permit direct embedment of the poles. Design of embedment parameters will be the responsibility of the selected utility/transmission vendor based on the final pole forces after all pole and line connection geometry has been selected.

For poles with line angles outside of the 5° tangent range, we have calculated ground-level forces from a static analysis as follows:

o Lateral loading at top of poles (unfactored) is equal to the final cable tensions described in Section 2.2.8 above for each connected cable.

o Vertical loading at ground level is based on the design weight of cables described in Section 2.2.8 above for each connected cable (unfactored) and an added self-weight of steel poles (factored) equal to 2,500 lbs for the blue and magenta lines and 3,500 lbs for the red line.

o Groundline moments are based on a 45’ height of cables for the blue and magenta lines and 42.5’ height of cables for the red line.

o Load Factors for all unfactored values above have been derived from USDA RUS Bulletin 1724E-200 using RUS criteria.

Based on the assumptions described above, we have provided four (4) caisson designs that have been developed by using the above factored vertical, lateral, and base moments as loading inputs at the top of the caisson and using a 3D soil model to determine the internal concrete forces. The loading limits for the provided caisson designs are as follows:

Caisson ID Max Vertical Load (kip)

Max Lateral Load (kip)

Max Groundline Moment (kip-ft)

C1 4.0 18.0 800.0 C2 4.0 34.0 1,500.0 C3 4.5 64.0 2,700.0 C4 5.0 90.0 3,800.0

If, after accounting for the effects of the final pole geometry on the vertical, lateral, and groundline moment loading, the loads on any pole exceed the limits state above then the foundation must be re-approved or re-designed by a licensed engineer.

2.4.3 Foundation Design Calculations

Slab on grade foundations have been designed for deadend poles 1-1 and 2-1, the pre-engineered “E-House” building, and the new capacitor bank. Foundations were analyzed with the loading described below using a 3D soil model to determine internal concrete forces based on elastic soil responses with notes and assumptions as follows:

All slab on grade foundations will include turn-down edges to provide additional lateral resistance to sliding and heaving that may be caused by the presence of expansive soils at the site.

Deadend pole slabs have factored base forces developed based on the criteria described in Section 2.2.7 above, using RUS Load Factors. Size and location of slab is based on information developed by electrical engineers, if the final selected poles result in increased base forces then the foundation must be re-approved or re-designed by a licensed engineer.

Pre-engineered “E-House” building slab has been designed based on a provided “go-by” model by Trachte for a pre-fabricated building of similar size and use. The relevant load and geometry criteria for the “go-by” are provided below. If the final submitted pre-fabricated building design varies from these listed parameters, then the foundation must be re-approved or re-designed by a licensed engineer.

o Building description – 44’-2” L x 17’-0” W x 11’-6” H (at eave), gable roof at 1:12 slope, building is supported on ten (10) concrete pedestals arranged in five (5) equally-spaced rows along the building length. Top of pedestals are assumed to be 3’-0” above main slab.

o Building Dead Load = 44 kip, per Bill of Materials (BOM) o Building Live Load = 250 psf, per ASCE/SEI 7. BOM lists equipment load as 33 kip, equivalent to less than 150 psf in the drawing area, with additional room for new equipment and so ASCE/SEI 7 loading will be used for potential future loading conditions.

o Building Live Roof Load = 30 psf, per BOM The capacitor bank slab on grade has been designed for a 500 psf “checkerboard” loading pattern to produce maximum slab reactions in the absence of vendor drawings or “go-by” reference drawings. When the final submitted capacitor equipment is delivered for construction, the foundation must be re-approved or re-designed by a licensed engineer.

2.4.4 Guy Wire Design

At this time, we have not included guy wire supports to reduce the lateral loading on the pole foundations. The utility equipment vendor providing steel pole design may choose to utilize guy wires in accordance with the project specifications if they are required or requested by the client.

2.5 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 before performing maintenance and allow drivers at least one (1) minute to discharge after disconnecting power. Follow manufacturer’s instructions when opening and closing the access door for maintenance. Ensure proper alignment and seal after the 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

Transmission Pole Forces Calculations LPILE Caisson Calculations

Caisson Concrete Calculations

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

Page From:

IEEE C2-2017 National Electric Safety Code (NESC)

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

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.

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.

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

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…