J.017 FAA Order JO 6950.27B - Power System Studies.pdf

Distribution: Electronic Initiated By: AJW-22

ORDER

JO 6950.27B

Effective Date:

07/06/2022

SUBJ: Power System Studies

1. This order establishes the policy and procedures for power system studies, which are required to ensure that the power distribution system infrastructure that supports National Airspace System (NAS) facilities is adequate and resilient.

2. This order is intended to meet the regulations established by the Occupational Safety and Health Administration and the consensus standards established by the National Fire Protection Association (NFPA), including the National Electrical Code (NFPA 70), the Standard for Electrical Safety in the Workplace (NFPA 70E), and the Recommended Practice for Electrical Equipment Maintenance (NFPA 70B).

3. Electrical studies are an integral part of power distribution system design, operations, and maintenance. These engineering studies generally cover the following areas of power distribution system design:

a. Power load-flow analysis (PLFA)

b. Short-circuit analysis (SCA)

c. Protective device coordination analysis (PDCA)

d. Arc flash risk assessment (AFRA)

e. Harmonic analysis

f. Engineering design and maintenance-related studies required to ensure adequacy of the power distribution system.

4. The basic mission of the Federal Aviation Administration (FAA) is to provide the safest, most efficient aerospace system in the world. Power Services Group is responsible for providing electrical power of proper quality, reliability, maintainability, and availability that fully supports the operational requirements of the NAS. The underlying philosophy is to construct power distribution systems that are based upon fundamental engineering design principles and practices and will provide (1) continuity of service; (2) protection of people and equipment, and;

(3) selective fault isolation where needed in the electrical distribution system. The planning, design, and operation of these power systems require engineering studies to evaluate and ensure proper adequacy, reliability, and safety for the electrical power systems.

Jeffrey S. Planty Vice President, Technical Operations Services

Air Traffic Organization Policy

JO 6950.27B

ii

07/06/2022

RECORD OF CHANGES DIRECTIVE NO. JO 6950.27B

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SUPPLEMENTS OPTIONAL

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FAA Form 6000-25 (10/12)

07/06/2022 JO 6950.27B

Table of Contents

Paragraph Page iii

Chapter 1. General Information ................................................................................................. 1-1

1. Purpose of This Order ........................................................................................................ 1-1

2. Audience ............................................................................................................................ 1-1

3. Where Can I Find This Order ............................................................................................ 1-1

4. Cancellation ....................................................................................................................... 1-1

5. Explanation of Policy Changes .......................................................................................... 1-1

Chapter 2. Power Study: General Requirements ....................................................................... 2-1

1. Overview ............................................................................................................................ 2-1

2. Roles and Responsibilities ................................................................................................. 2-1

3. Analysis Decision Process ................................................................................................. 2-2

4. Engineering Assessment Guidelines .................................................................................. 2-2

5. Deliverables ....................................................................................................................... 2-5

Chapter 3. Power Load-Flow Analysis (PFLA) ......................................................................... 3-1

1. Overview ............................................................................................................................ 3-1

2. Objectives .......................................................................................................................... 3-1

3. Load Analysis .................................................................................................................... 3-1

4. PLFA Calculations ............................................................................................................. 3-1

Chapter 4. Short-Circuit Analysis (SCA) .................................................................................. 4-1

1. Overview ............................................................................................................................ 4-1

2. Objectives .......................................................................................................................... 4-1

3. Purpose ............................................................................................................................... 4-1

4. Procedure ........................................................................................................................... 4-2

5. Report Submission ............................................................................................................. 4-2

Chapter 5. Protective Device Coordination Analysis (PDCA) .................................................. 5-1

1. Overview ............................................................................................................................ 5-1

2. Objectives. ......................................................................................................................... 5-1

3. Purpose ............................................................................................................................... 5-1

4. Procedure ........................................................................................................................... 5-2

5. Coordination Guidelines .................................................................................................... 5-2

6. Report Submission ............................................................................................................. 5-3

Chapter 6. Arc-Flash Risk Assessment (AFRA) ....................................................................... 6-1

1. General Overview .............................................................................................................. 6-1

Table of Contents

Paragraph Page iv

2. Objectives .......................................................................................................................... 6-1

3. Purpose ............................................................................................................................... 6-1

4. Procedure ........................................................................................................................... 6-1

5. Report Submission ............................................................................................................. 6-2

Chapter 7. Harmonic Analysis ................................................................................................... 7-1

1. Overview ............................................................................................................................ 7-1

2. Objectives .......................................................................................................................... 7-1

3. Purpose ............................................................................................................................... 7-1

4. Calculations........................................................................................................................ 7-1

5. Report Submission ............................................................................................................. 7-1

6. Application of Harmonic Limits ........................................................................................ 7-2

7. Harmonic Analysis Calculation Considerations ................................................................ 7-3

Chapter 8. Administrative Information ...................................................................................... 8-1

1. Distribution ........................................................................................................................ 8-1

2. Background ........................................................................................................................ 8-1

Appendix A. Acronyms and Abbreviations A-1 Appendix B. Key Terms and Definitions B-1 Appendix C. Applicable Codes and Standards C-1 Appendix D. Power Study Decision Process Assessment Guidelines D-1 Appendix E. Load Analysis Report – Illustrative Example E-1 Appendix F. Power Study Report – Illustrative Example F-1 Appendix G. Protective Device Coordination – Illustrative Examples G-1 Appendix H. Circuit Breaker Trip Unit Settings H-1 v

List of Tables

Table Page Table 2-1: Determining the Need for a Study and Extent of Analyses per Project Type ...... 2-3

List of Figures

Figure Page Figure 2-1. Process Sequence of Steps for Implementation of JO 6950.27 .......................... 2-4

Figure 8-1. Delivery Process Flow Chart .............................................................................. 8-1 vi

This Page Intentionally Left Blank

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Chapter 1. General Information

1. Purpose of This Order. This order establishes the policy, procedures, and guidance to conduct the power system studies required to ensure adequacy and resiliency of the power distribution system infrastructure supporting National Airspace System (NAS) facilities. Federal Aviation Administration (FAA) Power Distribution Systems will provide (1) continuity of service; (2) protection of people and equipment, and; (3) selective fault isolation where needed in the electrical distribution system.

2. Audience. The audience for this order will typically consist of engineers, designers, technicians, and managers directly involved with a power system’s design, construction, renovation, installation, maintenance, and operation at FAA facilities. The audience may be FAA employees, or they may be employees of a firm working under a contract with the Government.

The reader is encouraged to review Order JO 3900.64 Air Traffic Organization Electrical Safety Program for additional information related to electrical hazards.

3. Where Can I Find This Order. You can find an electronic copy of this order on the Directives Management System (DMS) website at https://employees.faa.gov/tools_resources/orders_notices/. Or go to the MyFAA employee website, select “Tools & Resources” and then select “Orders and Notices”. This order is also available on the Power Services Group’s, Orders, Standards, and Specifications website:

https://my.faa.gov/org/linebusiness/ato/operations/facilities_engineering/power_services/ sys_eng_team/stand_specs.html.

4. Cancellation. This order cancels FAA Order 6950.27A, Power System Analyses: Load Flow Calculations, Short Circuit Analysis, Protective Device Coordination Studies, and Arc Flash Risk Assessment, dated April 13, 2016.

5. Explanation of Policy Changes. This revision extensively updates JO 6950.27A by enhancing requirements related to the design and engineering analysis associated with power system studies. The revisions incorporate informative guidance for how to conduct and prepare power system studies to ensure compliance with the order. Major and minor changes include the following:

a. Renaming the order from “Power System Analyses: Load Flow Calculations, Short Circuit Analysis, Protective Device Coordination Studies, and Arc Flash Risk Assessment” to “Power System Studies.”

b. A documented effort must be made to reduce the arc flash incident energy to the lowest level possible. The study report should include commentary for every location with calculated incident energy above 4 cal/cm2 for purpose of documenting the effort, such as reviewing the overcurrent protective device selection and settings, to achieve objective of reducing arc flash incident energy to the lowest possible levels with selected devices.

c. Adding informative material to standardize the implementation, submission, and approval process for power studies.

d. Making editorial revisions and updating referencing for codes and industry standards.

https://employees.faa.gov/tools_resources/orders_notices/ https://my.faa.gov/ https://my.faa.gov/ https://employees.faa.gov/tools_resources/orders_notices/ https://my.faa.gov/org/linebusiness/ato/operations/facilities_engineering/power_services/sys_eng_team/stand_specs.html

2-1

Chapter 2. Power Study: General Requirements

1. Overview. FAA projects, including the initial design and sustainment of equipment or infrastructure, typically involve some level of electrical power design. This chapter provides criteria for determining when and to what extent a power study is needed and the roles and responsibilities of those undertaking it.

a. Power studies include analysis covering the following areas:

(1) Power load-flow analysis (PLFA)

(2) Short-circuit analysis (SCA)

(3) Protective device coordination analysis (PDCA)

(4) Arc-flash risk assessment (AFRA)

(5) Harmonic analysis.

Note: Harmonic analysis is not required in every power study/project. When a contract document specifically calls for a harmonic study to be conducted, it shall follow the procedure described in this order.

b. Power systems analyses of alternating-current (ac) and direct-current (dc) facility power distribution systems shall be accomplished in accordance with the following:

(1) National Electric Code (NEC)

(2) FAA-STD-032, Design Standards for National Airspace System Physical Facilities

(3) Institute of Electrical and Electronic Engineers (IEEE) Standard 399, IEEE

Recommended Practice for Industrial and Commercial Power Systems Analysis.

c. These analyses shall be accomplished as part of the project design submission and deliverable process.

2. Roles and Responsibilities.

a. The FAA organization providing engineering leadership for the project (program office or project level organization responsible for the system design) shall be responsible for ensuring the power system calculations described in this order are properly performed. The analyses shall show that values in the study meet or exceed and do not compromise the FAA's performance objectives for the electrical systems. The distribution system design must provide efficient, convenient, and adequate power service, and incorporate future expansion provision (where required).

b. The FAA program office requesting the power system project (for example, AJW-221) and the lead project engineer responsible for the installation or modification will share the responsibility for performing PLFA, SCA, PDCA, AFRA studies. The FAA program office will be responsible for (1) performing electrical power analyses in accordance with this order and based upon type of project being implemented; (2) reviewing calculation submittals performed by design firms, and; (3) archiving project calculation submittals in the power calculations

2-2 module of the Facility Power Panel Schedule database according to Order JO 6080.1, Facility Power Panel Schedule (FPPS).

c. The Environmental and Occupational Safety and Health (EOSH) program office, AJW- 23, will provide technical guidance on implementing the electrical safety requirements and oversight responsibilities for compliance with the National Electrical Safety Program.

d. Qualified engineers shall prepare the power studies required by this order. Qualified engineers are registered or certified professional electrical engineers or FAA electrical engineers.

The qualified engineer shall have at least 5 years of experience independently conducting and interpreting the power system analyses covered in this order.

e. The power systems analyses, and studies shall be used as the basis for specifying the rating and selecting the type of protective devices. To ensure that this requirement is met, Statements of Work (SOW) shall include requirements for power system analyses as described in this order, IEEE Std 399, IEEE Recommended Practice for Industrial and Commercial Power Systems Analysis, and other IEEE color book series.

f. The appropriate NAS equipment program office in coordination with the power distribution system Resident Engineer will coordinate NAS electronic systems and equipment.

This order addresses protection and overcurrent protective device (OCPD) coordination requirements for the power distribution system from power source to the end-of-line branch circuit panelboard circuit breaker devices that supply power to the electronic equipment. FAA- G-2100 addresses the OCPD requirements within the electronic equipment and subsystems. This order intends for the equipment interface connection point at facility branch panelboard OCPD to be coordinated.

3. Analysis Decision Process.

a. The FAA organization providing electrical engineering leadership for the project, in consultation with Engineering Services, the District/System Support Center (SSC) manager, EOSH, and other Program managers as appropriate, will determine whether there is a need to conduct a full analysis and calculations. The assessment process can take place in the planning or in design phase and shall be determined as follows:

b. In general, modifications such as changes to short-circuit current, protective device ratings or adjustment settings, or calculated incident energy levels, or any equipment modification that invalidates existing AFRA warning labels, requires a power study.

c. If the site, district, service area, or program office cannot agree upon the level of study required, the issue will be elevated to the Power Services Group, AJW-22, for resolution.

4. Engineering Assessment Guidelines. The engineer shall assess the project and consider factors that will influence parameters associated with power load-flow and short-circuit calculations, protective device coordination analysis, and arc-flash hazard analysis. Refer to the following:

a. Table 2-1 for project type related to the assessment and decision process for determining when to conduct a study.

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b. Figure 2-1, Process Sequence of Steps for Implementation of JO 6950.27, for a description of end-state deliverable framework.

c. Figure 8-1, Delivery Process Flow Chart, for guidance related to typical compliance paths based on the project type and assessment determination criteria.

Table 2-1: Determining the Need for a Study and Extent of Analyses per Project Type

Project Category Load

Analysis PLFA SCA PDCA AFRA Remarks

New building design and construction 1 1 1 1 1 —

Building renovation of power distribution system 2 1 1 1 1 3

Equipment modification 8 4 4 4 4 —

Equipment replacement 8 4 4 4 4 —

Equipment form/fit/function replacement

8 5 5 5 5 6

Addition of alternative energy power sources 2 7 7 7 7 —

Facility 5-year assessment update 8 7 7 7 7 —

Existing facility power study documentation unavailable

8 7 7 7 7 —

Notes:

1. Provide complete power study submission in accordance with the project design deliverable process.

2. Develop Load Analysis summary table during initial design submission in accordance with the project or program planning requirements document.

3. Existing Facility Power Panel Schedule (FPPS) data may be used to establish the Load Analysis information.

4. Refer to Appendix D for assessment conditions. Update analysis as applicable.

5. Refer to Appendix D for form/fit/function assessment conditions. Update analysis as applicable.

6. Analysis is not required for equipment replacement of same type, model, and specification.

7. Update FPPS data and power study documentation per JO 6950.27B.

8. Analysis is not required.

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Figure 2-1. Process Sequence of Steps for Implementation of JO 6950.27

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5. Deliverables. The power studies shall be incorporated into the project design data handbook in accordance with FAA-STD-032 deliverable requirements. A copy of the power studies should be provided to the installation contractor. The installation contractor shall be responsible to maintain the power study documentation through the project commissioning process. If changes or deviations from the approved design study are made, the installation contractor shall revise affected portions of the studies to reflect those changes or deviations. The installation contractor's scope of work specifications shall require the contractor to prepare and submit those revised portions of the studies as part of final system acceptance and record documentation submissions. Additionally, the contract specifications shall require the contractor to submit, as a minimum, one hard copy and one computer-readable media copy (soft copy) of each study. The study documentation and submission process shall include the following information:

a. Provide a report prepared in accordance with each chapter’s submission requirements.

The report shall provide the calculation performed for the analyses, including computer analysis programs utilized. The name of the software package, developer, and version number shall be provided.

b. Computer Software Program: Prepare study using the latest revision of the SKM Systems Analysis Power*Tools for Windows (PTW) software program.

c. Provide copies of the report and results in electronic format, referenced to the power one-line diagram and calculation model input parameters.

d. Provide the software program's native calculation model, program data files, and data collection information used in the study. The calculation model and data files shall be in a format for use by the site to perform analysis or recreate the calculations.

e. The coordination study shall be completed and submitted to FAA within a mutually agreed time prior to completion of the approved design. The results of the study shall be incorporated into the design as applicable. A copy of the approved report shall be included as part of the Design Data Handbook in accordance with FAA-STD-032. The study shall be conducted as early as practically possible in the design phase and shall be updated with every following submission.

f. The settings of the overcurrent and ground-fault protective devices shall be verified during commissioning and modified if needed.

g. Copies of the native software program files, library files, calculations, analyses, and studies submitted and accepted final documentation shall be deposited in the FPPS database system in accordance with documentation archive process by the office responsible for the project. The native program files shall be provided to the FAA, upon request, during submission deliverable and approval process to validate and review accuracy of the model and report.

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Chapter 3. Power Load-Flow Analysis (PFLA)

2. Overview. A PLFA includes the following parts:

a. Load analysis

b. Power load-flow calculations.

3. Objectives. Determination of following parameters:

a. Determination of system(es) power load requirement, (Load analysis)

b. Determination of power operating loading conditions, (PLFA)

c. Determination of power system voltage conditions, (PLFA).

4. Load Analysis. Provide a summary tabulation estimate for the power distribution system demand load requirement.

a. The load analysis is the starting point for project planning and initial design approval process.

(1) Purpose. The load analysis provides the basis for power system calculations and distribution equipment selections. The project planning and initial design requires careful collection of data, verification, and documentation of the basis of design (BOD).

(2) Load Analysis Report Submission.

(a) Provide an itemized summary of the power distribution system demand load requirement.

(b) Designer should use power system demand loading information based on metered data whenever possible, for determination of distribution equipment sizing and selection requirements. When metered data is not available, use demand and system diversity factors or established loading data from similar FAA facilities.

(c) Equipment nameplate data may be used to determine the branch distribution connected power loads.

(d) Consideration for future growth and spare device/space requirements should be addressed during the scoping of the project. The assessment for spare capacity should include input from facility/regional office leadership.

Note: Design main service equipment to provide approximately 15% combination of spare devices/space to accommodate future work. Include this 15% spare capacity in the demand load calculations for future or anticipated load growth.

5. PLFA Calculations. Determine active and reactive power, voltage, current, and power factor throughout the electrical system. The analysis shall include possible system power-flow operating scenarios.

a. PLFA results provides the basis for validation of the distribution system architecture.

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b. The PLFA calculation model is the starting point for short-circuit and protective device coordination analyses.

(1) Purpose. The power load-flow analysis provides the basis for determine the normal operating parameters of the power distribution system. The results of the PLFA calculations shall determine the following parameters:

(a) Commercial utility service entrance equipment peak demand load requirement

(b) Alternate power source equipment sizing requirements

(c) Power feeder conductor and conduit sizing requirements

(d) Power feeder voltage-drop calculations.

(2) PLFA Report Submission. Provide a power load-flow report containing the following items:

(a) Basis, description, purpose, and scope of the study

(b) Tabulations of the data used to model the system components and a corresponding power one-line diagram

(c) Description of power flow operating scenarios

(d) Power load-flow scenarios and voltage-drop calculation results annotated on the calculation model one-line diagram

(e) Tabulation of results consolidated into a summary report.

4-1

Chapter 4. Short-Circuit Analysis (SCA)

1. Overview. Short-circuit calculation is a fundamental part of power engineering. Perform an SCA before finalizing the distribution system layout, system voltage levels, and sizing of feeder conductors and transformers. For existing systems, fault-current analysis is necessary in cases where changes are made to power source equipment short-circuit contribution, motor loads are added, feeder system layout is modified, protection equipment is rearranged, or when conducting analyses involving determination of existing OCPDs adequacy.

2. Objectives. Determine the magnitude of short-circuit current flow throughout the distribution system at various time intervals after a fault occurs. Provide analyses of salient power-flow operating scenarios such as commercial utility, generator, and maintenance tie circuit connection power operating modes. Calculate the following fault-current conditions:

a. Three-phase bolted-fault

b. Single line-to-ground faults

c. Double-line-to-ground faults

d. Line-to-line faults.

Calculate short-circuit currents for following time frames:

a. Momentary, 1/2 cycle currents

b. Interrupting, 3 and 5 cycle currents

c. Time delayed, 30 cycle currents.

3. Purpose. The short-circuit analysis shall calculate ac and dc short-circuit currents in accordance with American National Standards Institute (ANSI)-approved standards. The results of the SCA calculations are to be used to validate the application of short-circuit momentary and interrupting duties for equipment used in the power distribution system. Application considerations shall compare SCA results against the power distribution equipment ratings. The SCA results shall include the following parts:

a. Calculate short-circuit momentary and interrupting duties for a three-phase bolted fault throughout the distribution system.

b. For grounded systems, provide a bolted line-to-ground fault-current study for areas as defined for the three-phase bolted fault short-circuit study.

c. Protective device evaluation:

(1) Evaluate equipment and protective devices and compare to short-circuit ratings

(2) Evaluate adequacy of the distribution system equipment ratings to withstand short-circuit stresses

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(3) Identify areas where circuit protective devices are improperly rated for the calculated available fault-current.

4. Procedure. The short-circuit study shall be performed in accordance with the recommended practices and procedures set forth in ANSI/IEEE Std-399, and the step-by-step procedures outlined in the short-circuit calculation chapters of IEEE Std-141, IEEE Std-551.

a. Include the utility system data as well as data for the distribution system. When accurate data does not exist, assume that maximum available fault-current contribution exists, up to a possible infinite bus on the primary side of the upstream transformer, and design the system and equipment interrupting ratings assuming such conditions. Create additional short-circuit scenarios to estimate the commercial utility maximum/minimum short-circuit contribution when determining the worst-case arc flash arcing fault conditions. For systems with power generation equipment, include a short-circuit scenario for generator power load flow condition.

Note: In absence of known utility SCA data use minimum 100MVA SCA and maximum 500MVA SCA with value of 16 for X/R ratio for utility power source contribution.

b. Calculate the available short-circuit and ground-fault currents at each equipment bus.

c. Motor load short-circuit contribution may be estimated using ANSI-approved standard applications guides, refer to IEEE Std-551, section 6.8 in the absence for detailed motor load information.

d. Coordinate the calculated short circuit current at the service entrance with the available fault-current labeling required by the NEC for the service entrance equipment. Comply with IEEE C37.06, IEEE C37.13.1, or UL 489 criteria, as applicable, for equipment interrupting capability.

e. Final design studies shall be based on utility available fault-current contribution data calculated at the facility power service demarcation point.

f. Final design studies shall use PLFA calculation model results for determination of system motor load contribution.

5. Report Submission. Results of the short-circuit study shall be summarized in a final report containing the following items:

a. Basis, description, purpose, and scope of the study.

b. Tabulations of the data used to model the system components and a corresponding one-line diagram.

c. Descriptions of the scenarios evaluated, and identification of the scenario used to evaluate equipment short-circuit current ratings.

d. Tabulations of power and current flow versus equipment ratings. The tabulation shall identify percentage of rated load and the scenario for which the percentage is based. Overloaded equipment shall be clearly noted.

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e. Tabulations of equipment short-circuit current ratings versus available fault duties. The tabulation shall identify percentage of rated short circuit current and clearly note equipment with insufficient ratings.

f. Conclusions and recommendations.

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Chapter 5. Protective Device Coordination Analysis (PDCA)

1. Overview. Overcurrent protection and coordination is a fundamental requirement for proper operation of the power system. A PDCA is the comparison and selection of protective device operating times that achieves the objectives of the protection system under abnormal system conditions.

2. Objectives. Determine the characteristics, ratings, and settings of overcurrent protective devices that minimize equipment damage and interrupt short-circuits as rapidly as possible. The PDCA shall determine the following parameters:

a. OCPD ratings and settings

b. Overall system protection scheme

c. Distribution equipment to ensure adequate system protection and selectivity

d. Evaluate and coordinate the system protection scheme to mitigate arc-flash incident energy levels without compromising system protection and selectivity objectives.

3. Purpose. Selective coordination is both an art and a science. A perfectly coordinated system cannot always be accomplished. It is the responsibility of the design engineer to maximize coordination to the extent practical. The designer shall strive to achieve the following coordination objectives:

a. Protection of people and equipment

b. Continuity of power service

c. The power distribution system protective devices should coordinate to a level such that no conductor, device, or circuit not directly critical to the safety function of Air Traffic systems, should ever cause or allow an interruption in service continuity to any device or circuit necessary for NAS safety. FAA critical power distribution systems (CPDS) may contain redundant power paths for reliability and maintainability. CPDS power paths shall achieve the following coordination objectives:

(1) Coordination of redundant power systems shall coordinate to a level such that a fault on power path A, of a dual redundant distribution system, will not disrupt or interfere with the operation of power path B distribution system.

(2) Ensure selective coordination in the power path to critical loads. Total selective coordination is required to the available fault current between the load panelboard branch circuit breakers and the upstream protective devices, such as the panelboard main and upstream feeder protective devices.

(a) Exception: Total selective coordination may not be possible in existing facility power systems. The intent is to update the power system to extent possible within project funding constraints. The initial project planning process must assess system capabilities and address study requirements in the SOW. Where it is not possible to achieve total selective coordination due to lack of funding, the report must document the requirements/upgrades needed

5-2 to achieve selective coordination for future project consideration. The Office of Primary Responsibility (OPR) should be contacted to obtain technical guidance on the applicability of requirements herein for modifications, upgrades, and new equipment installations in existing facilities.

d. Power system load continuity requirement may be considered in coordination selectivity analysis. The following conditions should be part of PDCA:

(1) Unmanned NAS facilities and facility power circuits that supply power to equipment that directly controls the landing of aircraft, cannot tolerate power service interruptions and require selective coordination of protective devices. When difficulty is encountered meeting this requirement, consult the OPR of this document.

(2) Facility essential subsystem power loads, such as a chiller motor connected to the essential bus, may have less stringent selective coordination requirements. Redundant power distribution feeds should be considered for these conditions to improve system reliability.

4. Procedure. The coordination study shall be performed in accordance with the recommended practices and procedures set forth in ANSI/IEEE 399, Brown Book, and ANSI/IEEE 242, Buff Book. Protective device selection and settings shall comply with the system protection requirements of the NEC.

a. The maximum available-fault current or fractions of the maximum available fault-currents shall be used for the PDCA studies. PDCA, time-current coordination shall be based on the commercial utility available short-circuit data and the power systems installed equipment short-circuit contribution data.

b. AFRA, risk mitigation shall be coordinated during the PDCA process. AFRA shall consider both maximum and minimum short-circuit contribution data for PDCA, time-current coordination.

c. Ground fault protection coordination shall be a part of the report analysis. OCPD ground fault protection settings and sensing signals shall be verified during the commissioning in accordance with NEC requirements.

5. Coordination Guidelines. The following guidelines are intended to assist the PDCA process:

a. Use the national standard designs for Critical Power Distribution System, Program Implementation Plan (P6980.00), wherever possible. Implementation of these designs or other non-standard designs should include engineering and selection of distribution OCPDs to achieve the systems coordination objectives. The following device selection considerations may be included in the design:

(1) Use electronic, solid-state, circuit breakers with adjustable trip unit functions for main and feeder OCPD locations when this option is available for distribution equipment selection. Selection of adjustable trip device types is recommended to improve coordination discrimination and mitigate arc flash incident energies.

(2) Dynamic impedance. Dynamic impedance is not reflected in the instantaneous region of published time-current curve (TCC) graphical representations. OCPDs shall be selected based

5-3 on manufacturer's published selectivity and coordination test data when such data is available.

Actual time-current TCC graphical representation is still valuable in long-time and short-time regions.

(3) Use OCPDs with large frame sizes at power source equipment mains and feeder branch locations where selectivity improvement in the instantaneous region is desirable.

Selection of device frame size and frame size pairing combinations must be coordinated with manufacturer’s application tables for selective coordination.

(4) Elimination of panelboard main circuit breaker devices may be considered, for purpose of minimizing the number of OCPDs along the coordination path, where the protection scheme is not compromised, however, in all cases system protection shall comply with the NEC.

The CPDS standard design configuration utilize instances where multiple overlapping protective devices in series are desirable, such as feeder and main circuit breaker combinations. These instances are commonly used for isolation purposes and provide a means for secondary protection to achieve desired selectivity at other points in the distribution system where coordination is paramount.

(5) AFRA generally requires fast short-time response characteristics. Consider setting the I2T short-time delay feature to out/off setting whenever possible.

(6) Ground-fault protection may be added to protective device trip unit functions to detect and interrupt arcing fault-currents for AFRA risk mitigation.

(7) AFRA arc energy reduction systems shall be provided in accordance with NEC requirements. Preferred method to reduce device clearing time, in absence of OCPD trip unit adjustment settings, should use an energy-reducing maintenance switching scheme with local status indicator integrated into the distribution equipment layout.

b. Fire life safety systems, such as: fire alarm, emergency exit/egress lighting, fire pump, stair pressurization system, and elevator equipment shall be coordinated in accordance with NEC requirements.

c. Obtain available short-circuit contribution data from the commercial utility during initial design process.

d. Ensure that feeder conductors are selected to coordinate with the conductor protective device. The conductors thermal damage curve should not overlap the OCPD TCC in the instantaneous region.

e. Ensure that equipment protective devices are selected to coordinate with the equipment inrush-current requirements.

6. Report Submission. Results of the coordination study shall be summarized in a report containing the following items:

a. Basis, description, purpose, methods and scope of the study, and a corresponding one-line diagram.

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b. Time-current curves, selective coordination ratios of fuses, or selective coordination tables of circuit breakers demonstrating the coordination of overcurrent protective devices to the scope.

c. Tabulations of protective devices identifying circuit location, manufacturer, type, and range of adjustment, and IEEE device number, and referenced TCC.

d. Tabulation of protective devices to summarize the settings selected for each protective device. Provide the following information as applicable:

(1) Recommended settings or protective device type selection

(2) Device identification name and associated load controlled

(3) Circuit breaker sensor rating

(4) Fuse type and rating.

(5) Relay current-transformer (CT) ratios and electronic set point equivalents for relay tap, time-dial settings, and instantaneous pickup points.

(6) Ground-fault pickup and time delay settings

(7) Differential relay settings

(8) Current transformer ratios.

e. Conclusions and Recommendations.

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Chapter 6. Arc-Flash Risk Assessment (AFRA)

1. General Overview. Arc-Flash analysis is a fundamental power system design requirement.

The design requires an iterative process to ensure proper system protection, selective coordination, and reduction of arc flash incident energies.

2. Objectives. Determine arc-flash incident energy levels and arc-flash protection boundary distances based on the results of the short-circuit and coordination studies. The analysis must determine the worst-case arc-flash conditions for power system operating modes.

The AFRA shall be performed to calculate the arc-fault current and incident energy values for each element in the facility power system or Electrical Line Distribution (ELD) project power system. The study shall include the following:

a. The AFRA shall calculate incident energy associated with 100% available fault-current and 50% of available fault-current contribution. Utility data must be used for the 100% available fault-current level.

b. Evaluate distribution equipment to ensure adequate system protection and selectivity.

c. Evaluate and coordinate the system protection system settings to mitigate arc-flash incident energy levels without compromising system protection and selectivity objectives.

d. Documented effort must be made to reduce incident energy to the lowest levels possible.

3. Purpose. Determination of following parameters:

a. Equipment arc-flash warning label parameters.

b. Prepare equipment arc-flash warning labels in accordance with Air Traffic Organization Electrical Safety Program (JO 3900.64) requirements.

4. Procedure. Calculate the arcing fault current flowing through each branch for each fault location in accordance with NFPA 70E, IEEE 1584, and Occupational Safety and Health Administration (OSHA) 1910.269 applicable standards.

a. Collect the system and installation data and prepare a one-line diagram of the power system.

b. Determine system operating modes including tie-breaker positions, and parallel generation configurations.

c. Perform a short-circuit study in accordance with Section SCA.

d. Perform a coordination study in accordance with Section PDCA.

e. Determine the time required to clear the arcing fault current using the protective device settings and associated trip curves.

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f. Determine typical gap and enclosure size based upon system voltages and equipment classification.

g. Determine the equipment electrode configuration.

h. Select the working distances based on system voltage and equipment classification.

i. Calculate the incident energy at each fault location at the prescribed working distance.

j. Determine the arc-flash hazard personal protective equipment (PPE) category for the calculated incident energy level.

k. Calculate the arc-flash protection boundary at each fault location.

l. Document the assessment in reports and one-line diagrams.

m. Fabricate and install equipment warning labels on distribution equipment in accordance with Order JO 3900.64.

5. Report Submission. Results of the arc-flash hazard study shall be summarized in a final report containing the following items:

a. Basis, method of hazard assessment, description, purpose, scope, and date of the study.

b. Tabulations of the data used to model the system components and a corresponding power one-line diagram.

c. Document selection of the equipment electrode configurations.

d. Provide annotated power one-line diagram showing input data and arc-flash results data for each equipment bus according to each study scenario.

e. Descriptions of the scenarios evaluated, and identification of the scenario used to develop incident-energy levels and arc-flash boundaries.

f. Tabulations of equipment incident energies, arc-flash hazard PPE categories, and arc-flash boundaries. The tabulation shall identify and clearly note equipment with prohibited energized work locations that exceeds 40 cal/cm2 incident energies.

g. Conclusions and recommendations.

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Chapter 7. Harmonic Analysis

1. Overview. Harmonic analysis includes the following parts:

a. Calculation of harmonic bus voltages and branch current flows in the power distribution system due to harmonic sources.

b. Performance indices that calculate the effects of harmonics on voltage or current waveform distortion.

c. Conduct calculations in accordance with IEEE Std 519 IEEE Recommended Practice and Requirements for Harmonic Control in Electric Power Systems, 3/27/2014.

2. Objectives. Determination of following parameters:

a. Prepare a system power one-line diagram.

b. Gather nameplate data and ratings for harmonic generating equipment.

c. Determine location of nonlinear loads and the generated harmonic currents.

d. Obtain from the power utility company the relevant data and harmonics at the PCC.

Provide the following information as applicable:

(1) The short-circuit capacity and X/R ratio of the utility power system at PCC.

(2) Subtransient reactance and kVA rating of rotating machines large than 50hp.

(3) Reactance and resistance of power feeders and current limiting reactors part of the distribution system one-line diagram.

(4) Three phase power transformer kVA rating and percent impedance values.

(5) Permissible limits on harmonics including distortion factors and IT factor per.

3. Purpose. The harmonic analysis provides information to verify adequacy of power system calculations and distribution equipment selections. The project planning and initial design requires careful collection of data, verification, and documentation of the BOD.

4. Calculations. The analysis shall include system salient power-flow operating scenarios such as utility and generator power operating modes.

a. Calculate individual and total harmonic voltage and current distortion factors and applicable IT values at the point of common coupling.

5. Report Submission. Provide a report containing the following items:

a. Basis, description, purpose, and scope of the study.

b. Tabulations of the data used to model the system components and a corresponding power one-line diagram.

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c. Description of power flow operating scenarios.

d. Tabulation of individual and total harmonic voltage and current distortion factors and applicable IT values at the point of common coupling.

e. Tabulation of results consolidated into a summary report.

f. Provide recommendation for harmonic mitigation approach for systems that exceed permissible distortion limits.

6. Application of Harmonic Limits. IEEE 519 provides recommended harmonic voltage and current limits applicable at the PCC. Harmonic voltage limits are characterized by total harmonic distortion percentage. Harmonic current limits are characterized by total demand distortion

(TDD).

a. IEEE 519 harmonic limits apply only at the point of common coupling and should not be applied to either individual pieces of equipment or at locations within the facility.

b. The PCC is intended to be applied at the point of demarcation between the commercial electric utility distribution system and the facility’s power distribution system.

(1) In general, the PCC is located at the primary side of the facility service transformer.

(2) The IEEE standard allows for the same harmonic analysis procedure to be applied at other locations of interest within a facility where it is important to ensure adequate power system operation, such as a facility’s main distribution point, or the interface point for on-site power generation equipment.

(3) A facility with multiple commercial utility power feeds may have multiple PCC utility interface locations.

c. Provide harmonic analysis calculations for the facility PCC and other key distribution points.

(1) The facility main distribution point may be located on the secondary of the incoming utility service if access to the primary distribution system is not available.

(2) Sites with power generation equipment should include harmonic analysis for load flow scenarios connected to the generator system.

(a) Determine appropriate power load flow scenarios to establish a basis for the system demand load requirement. The demand load should be normal steady-state operating condition.

(b) Generator system TDD harmonic current limits must be based on IEEE 519, Table 2, note-c, exception values. The harmonic analysis must consider overall power system voltage and power factor stability requirements when implementing harmonic mitigation equipment.

(i) If TDD harmonic limits cannot be achieved without effecting the generator system performance throughout all power load flow scenarios, or in absence of abnormal operating conditions, the harmonic current distortion limits may be exceeded to ensure stability of the generator power system.

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(ii) Passive harmonic filtering equipment that may alter system power factor, impedance, and harmonics as demand load scenarios change should be avoided.

(iii) Harmonic mitigation equipment must include features to disable filtering if the connected power load is not operating within the filter design specifications.

7. Harmonic Analysis Calculation Considerations. The harmonic calculation model should include the following power system components:

a. Commercial Electric Utility:

(1) The utility short-circuit data and power system demand load requirement must be obtained to establish a basis for system short-circuit ratio.

(2) Short-circuit ratio is the ratio of the available…