J.20 FAA Order 6950.27A.pdf

U.S. DEPARTMENT OF TRANSPORTATION ORDER

FEDERAL AVIATION ADMINISTRATION 6950.27A

National Policy

Effective Date:

04/13/2016

SUBJ: Power System Analyses: Load Flow Calculations, Short Circuit Analysis, Protective Device Coordination Studies, and Arc Flash Risk Assessment

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 a quality, reliability, maintainability, and availability that fully supports the operational requirements of the National Airspace System (NAS). Well-designed systems are a necessity, not a luxury.

Electrical power engineering calculations, analyses, and studies are necessary to maximize personnel safety, and minimize equipment damage and unscheduled facility outages caused by unanticipated operation of protective devices. The goal is to have a power distribution system serving NAS facilities that is properly rated for nominal voltage, load current, and fault current, and will provide (1) continuity of service; (2) protection of people and equipment; (3) selective fault isolation where needed in the electrical distribution system. Failures of improperly applied power protective devices are a safety hazard to installation and maintenance personnel.

Application of uncoordinated protective devices also degrades the reliability and availability of facility power distribution systems.

Calculations together with the accumulated lessons learned are the basis for making decisions during the design phase of an electrical power distribution system.

Vaughn A. Turner Vice President, Technical Operations Services

Distribution: Electronic Initiated By: AJW-221

04/13/2016 6950.27A

Table of Contents

Chapter 1. General Information 1-1. Purpose of This Order 1-2. Audience 1-3. Where I Can Find This Order 1-4. Cancellation 1-5. Explanation of Policy Changes

Chapter 2. Power System Analyses 2

2-1. Implementation 2

2-2. Responsibilities 2

2-3. Deliverables 2-2

2-4. Systems and Equipment 2-3

2-5. Documentation Archive 2-3

2-6. General Requirements for Analyses 2-5

2-7. Specific Requirements for SCA 2-6

2-8. Specific Requirements for PDCA 2-6

2-9. Specific Requirements for AFRA 2-6

Chapter 3. Determining the Need for a Study 3-1

Chapter 4. Coordination Guidelines 4-1

Chapter 5. Administrative Information 5-1

5-1. Distribution 5-1

5-2. Background 5-1

5-3. Definitions 5-1

Appendix A. Power Systems Analyses and Calculations A-l

Appendix B. Setting Circuit Breakers B-1

B-1. Circuit Breaker Settings - Thermal-Magnetic Trip Units B-1

B-2. Circuit Breaker Settings - Electronic Trip Units B-4

Appendix C. Projects Requiring SCA and AFRA C-l

Appendix D. FPPS Data System D-l

List of Figures

Figure Page

1. Document Archive Process 2-4

2. Calculations Decision Process Flowchart 3-2

B-1. Typical Time-Current Characteristic Curve for Thermal-Magnetic Trip Unit B-1

B-2. Typical Time-Current Characteristic Curve for Thermal-Magnetic Trip Unit showing effect of Thermal Adjustment B-2

B-3. Typical Time-Current Characteristic Curve for Thermal-Magnetic Trip Unit showing effect of Magnetic Adjustment B-3

B-4. Typical Time-Current Characteristic Curve for Electronic Trip Unit B-4

B-5. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Long

Time Pickup Adjustment B-5

B-6. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Long

Time Delay Adjustment B-6

B-7. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Short

Time Pickup Adjustment B-7

B-8. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Short Time Delay Adjustment B-8

B-9. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Instantaneous Pickup Adjustment B-9

B-10. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Ground Fault Pickup and Delay Adjustments B-10 in

Chapter 1. General Information

1-1. Purpose of This Order. This order directs the accomplishment of power systems analyses and studies for alternating-current and direct-current, low/medium/high-voltage facility power distribution systems. Properly conducted analyses and studies ensure a design that is adequate, efficient, and convenient for the needs of the FAA, in addition to being safe. These studies include, but are not limited to, Short Circuit Analysis (SCA), Protective Device Coordination Analysis (PDCA), and Arc Flash Risk Assessment (AFRA). This order coordinates with the most current requirements of FAA Order 3900.19, FAA Occupational Safety and Health Program, FAA Order 3900.64, ATO Electrical Safety Program, National Fire Protection Association (NFPA) 70® National Electrical Code® (NEC), 29 CFR 1910 Subpart S— ELECTRICAL and Subpart I—Personal Protective Equipment (PPE), and NFPA 70E® Standard for Electrical Safety in the Workplace.

1-2. Audience. This order is for all FAA employees and managers who are involved in power systems design, installation, and operation. This would include Engineering Services, Environmental Support Unit Personnel, engineers and managers who review and/or approve designs from non-FAA engineering entities.

1-3. Where I Can Find This Order. You can find an electronic copy of this order on the Directives Management System (DMS) website https://emplovees.faa.gov/tools_resources/orders_notices/ or go to the MyFAA Employee website, select 'Tools and Resources', then select 'Orders and Notices'. This order may also be found on the Power Services Group, Orders, Standards and Specifications webpage https://employees.faa.gov/org/linebusiness/ato/operations/technical_operations/atc_facilities/pow er_services/stand_specs/

1-4. Cancellation. This order cancels Order 6950.27, Short Circuit Analysis and Protective Device Coordination Study, dated October 3,1994, including CHG 1 dated January 23,2003.

1-5. Explanation of Policy Changes. This revision incorporates various editorial changes, clarifications, and incorporates CHG 1 of the previous revision.

In addition, FAA Employee Occupational Safety and Health (EOSH) orders mandate a safe working environment, particularly regarding electrical work. These requirements include an Arc Flash Risk Assessment and proper equipment labeling. Calculated short circuit currents and time-current coordination curves are generally the basis for the arc flash risk assessment. In addition to the level of arcing fault current, the clearing time of the protective device is also a factor in determining the level of Incident Energy exposure to people and equipment. Proper selection and coordination of the protective device can minimize the risk, and still provide the required continuity of service.

1-1 https://emplovees.faa.gov/tools_resources/orders_notices/ https://employees.faa.gov/org/linebusiness/ato/operations/technical_operations/atc_facilities/pow

04/13/2016 6950.27A

Chapter 2. Power System Analyses

2-1. Implementation. Power systems analyses of alternating-current and direct-current facility power distribution systems shall be accomplished in accordance with the NEC and FAA standard, FAA-STD-032, Design Standards for National Airspace System Physical Facilities, and IEEE Std 399™, IEEE Recommended Practice for Industrial and Commercial Power Systems Analysis. These analyses shall be accomplished:

system (See Chapter 3 for a more detailed description of what is a "major modification".);

The goal is to have a power distribution system serving NAS facilities that is properly rated for nominal voltage, load current, and fault current, and will provide (1) continuity of service; (2) protection of people and equipment; (3) selective fault isolation where needed in the electrical distribution system; and (4) reduction of incident energy hazard; (5) adequately documented.

For all new construction and major electrical and Heating, Ventilation, Air Conditioning (HVAC) modifications, solid-state and thermal-magnetic circuit-breakers and other overcurrent protective devices should be considered and installed to help achieve better protective device coordination and to provide a function/feature to reduce Arc-Flash incident energy during inspection, maintenance, modification or any other work on or near energized circuits. Designs shall provide options for Zone Interlock, Current Limiting, Extreme Inverse Instantaneous function, Differential Relying and all other applicable incident energy reduction systems/options.

The Time-Current Characteristics (TCC) curves provided as part of the studies shall provide a clear understanding of the effectiveness of the various coordinated and protective results.

2-2. Responsibilities.

a. Projects shall incorporate the requirement to perform SCA, PDCA, AFRA studies.

Accomplishment of this requirement will be a shared responsibility between the program office requesting the power system project and the lead project engineer responsible for the installation / modification. The EOSH Services organization, AJW-23 will provide technical guidance on implementation of the electrical safety requirements as determined to provide oversight for compliance with the National Electrical Safety Program.

b. Only qualified engineers shall do SCA, PDCA, and AFRA required by this order.

Qualified Engineers are (1) registered or certified professional electrical engineers or (2) FAA Electrical Engineers. Engineers shall have 3 or more years of experience independently conducting and interpreting power systems calculations including Load Flow Analysis, SCA, PDCA, and AFRA. 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 IEEE Std 399™ IEEE Recommended Practice for Industrial and Commercial Power Systems Analysis.

2-1

2-3. Deliverables. The SCA, PDCA, and AFRA studies shall be a part of the design data summary handbook in accordance with FAA-STD-032. A copy of the studies will be provided to the installation contractor. If changes or deviations from the approved design are made, the installation contractor shall revise affected portions of the studies to reflect those changes or deviations. Installation contract specifications shall require the contractor to prepare and submit those revised portions of the studies. Additionally, the contract specifications shall require the contractor to submit, as a minimum, one hard copy and one computer-readable media (soft copy) of each study.

The study shall contain the following information:

a. An executive summary, which identifies all significant design shortfalls and recommended solutions.

b. A tabulation of all protective devices identified on the one-line diagram, with their ratings compared to their respective fault duty as calculated in the study. The same nomenclature shall be used throughout the project and shall be consistent with the drawings and the FAA facility standards.

c. A tabulation of the settings recommended on all adjustable protective devices with references to the single-line diagram and coordination curves. Providing only ranges of settings is not acceptable.

d. Copies of all TCC curves developed in the study including ground fault protection devices.

e. Copies of all TCC curves from manufacturer's datasheets.

f. An analysis of design shortfalls that lead to specific recommendations included in the executive summary.

g. A legible single-line diagram of the system studied, including short circuit current values, and description of all ratings and identifications described therein.

h. Copies of all results in electronic format, referenced to the single-line diagram and the impedance listing.

i. The electronic copy of the program files used for the site to perform the analysis shall be supplied upon request. The files provided will allow the FAA to recreate the calculations when inserted into software program.

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.

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

Copies of the calculations, analyses, and studies submitted and accepted shall be deposited in the FPPS (Facility Power Panel Schedule) Data System calculations database.

2-2

2-4. Systems and Equipment. Overcurrent Protective Devices (OCPD) within the equipment or subsystems and the interface to the facility power distribution system shall also be coordinated.

This requirement is incorporated in the last edition of Specification FAA-G-2100. This requirement shall be accomplished by appropriate program offices and coordinated with Resident Engineers.

2-5. Documentation Archive. The various power system studies shall become a part of Section IV of the Facility Reference Data (FRD) document, and the Power Calculations module of FPPS Data System. See Appendix D, FPPS Data System.

The Power Calculations module contains data survey forms which shall be used during all stages of the project life. For new designs, the survey forms shall be completed and uploaded for future use, such as periodic review of AFRA or facility modification.

For existing facilities, the survey forms shall be downloaded from the FPPS database reviewed, corrected, and/or completed as required, and uploaded for future use, such as periodic review of AFRA or facility modification.

Calculations shall be deposited in FPPS database.

If the power distribution system is modified in any way, then the base lined studies shall be updated and re-deposited in the electronic depositories. This includes branch or feeder breaker replacement. See Chapter 3 for detailed information.

The base lined studies shall be evaluated every 5 years and updated accordingly.

2-3

Figure 1. Document Archive Process

FAA Engineers download pre-prepared survey tables from FPPS Data System.

V

FAA Engineers populate pre-prepared survey tables for new and existing facilities.

i '

FAA Engineers upload the survey tables for new and existing facilities to the FPPS Data System.

i '

FAA Engineers and / or Contractors Engineers use accurate one line drawing and accurate survey forms to model the system.

FAA Engineers upload accurate calculations to the FPPS Data System.

i '

FAA Engineers update calculations, drawings, and survey tables as appropriate.

T

FAA Engineers update calculations, every 5 years to meet Arc Flash regulations requirements.

2-4

2-6. General Requirements for Analyses. The various Power System Analyses depend on other Power System Analyses. For example, an AFRA depends on the outputs of the SCA and PDCA. The SCA determines the fault current, and the various ratings of the electrical equipment. The PDCA determines the time required for overcurrent protective devices to isolate overload or short-circuit conditions. Results of both SCA and PDCA information needed to perform an AFRA. The AFRA identifies the flash-protection boundary and the incident energy at assigned working distances throughout any position or level in the overall electrical system.

Appendix A describes the various types of analyses that are necessary for a properly designed power system, and when each is required in the facility/project life.

The largest effort in an AFRA, especially in an existing facility, is collecting the field data. The largest effort in an arc-flash hazard study is collecting the field data. Even for a plant with nominally up-to-date single-line diagrams, time-current curves, and short-circuit study on a computer, thefield part of the study will take about half of the effort. Regular site employees who are familiar with the site and its safety practices may be able to do this part of the job best.

Use of the survey forms maintained in the FPPS Power Calculations Module will assist in this effort.

The engineer must use a current and accurate single-line diagram of the power system. This diagram shall identify all components considered in the study and the ratings of all power devices. This includes, but is not limited to, transformers, circuit breakers, relays, fuses, busses, and conductors. Reference numbers shall be used on the diagram related to key items in the report. American National Standards Institute (ANSI) device function numbers shall be used on protective relays.

The engineer must obtain the utility transformer data including transformer mega-volt-amperes (MVA) or kilo-volt-amperes (kVA), percent impedance %Z, primary and secondary voltage, electrical protection on primary and secondary, primary and secondary winding configuration, minimum and maximum utility contribution. If it is impossible to obtain the value for any of these parameters, consult FAA Power Services Group for guidance.

The engineer must also:

a. Provide recommendations on the use of electrical switchgear, switchboards and other electrical apparatus with features and devices for racking in/out power circuit-breakers and switches, and viewing windows for use of Thermal Imaging Instruments;

b. Provide a power distribution system design for non-essential, essential and critical power with a method to bypass downstream power with little or no interruption, to allow isolation and lockout of circuits, and providing a totally safe work condition;

c. Specify that all solid-state circuit-breakers be provided with a feature for connection and testing with a test-set that shall be provided as part of the project.

Most of the power distribution systems within FAA facilities are radial systems, not networked systems. The analysis of radial systems does not require use of Newton-Raphson or Gauss- Seidel methods commonly found in much commercial power analysis software. Use of commercial power analysis software is acceptable but not required. All calculations must be in accordance with established electrical power engineering principles.

2-5

04/13/2016 6950.27A

2-7. Specific Requirements for SCA. The maximum available fault current shall be used for the SCA studies.

A short circuit study shall be performed which shows the momentary and interrupting fault duties on each bus shown on the single-line diagram. Either computer or manual engineering analysis shall be used to perform calculations on all faults. In addition, an impedance listing shall be prepared showing bus-to-bus impedance values reduced to a common MVA base referenced to a single-line diagram for ease in reviewing data.

Study each over-current device calculated duty and recommend changes when appropriate.

2-8. Specific Requirements for PDCA. For each new or modified power distribution system design, a comprehensive PDCA shall be completed. The PDCA covers all devices and power sources identified on the single-line diagram.

The PDCA is required in the following situations:

may result in configuration management changes;

• When a NAS Change Proposal (NCP) is requested which directly affects the power system;

• When major power system modifications are made to existing facilities.

The maximum available fault current or fractions of the maximum available fault currents shall be used for the PDCA studies.

The ground fault protection coordination shall be a part of the report.

The ground fault protection setting shall be verified during the commissioning. Ground-fault protection shall be done as per NEC.

2-9. Specific Requirements for AFRA. Both maximum and minimum available fault current shall be used for AFRA studies.

The AFRA shall calculate incident energy associated with 100% fault current and 85% fault current. The outcome of the study shall be based upon whichever calculation yields the greater incident energy.

An arc-flash study shall be performed which shows the arc-fault current and incident energy values for each element in the facility or in the Electrical Line Distribution (ELD) project.

Calculations shall use accepted methods of IEEE Std 1584™-2002 IEEE Guide for Performing Arc-Flash Hazard Calculations, and NFPA 70E®, Standard for Electrical Safety in the Workplace, Annex D.

The AFRA calculates incident energy at each protective device and resolves any conflict between the time trip settings of the protective device and the desired reduction of incident energy as a function of time.

Labeling is a requirement of Order JO 3900.64, not JO 6950.27. Therefore, this order does not list labels as a requirement. JO 6950.27 will reference but not duplicate JO 3900.64.

Duplication can lead to confusion instead of clarity.

2-6

For each new or modified power distribution system design, an assessment of arc flash hazard covering all devices and power sources identified on the single-line diagram shall be completed.

See Chapter 3 for details regarding this assessment. Arc flash ratings, PPE, and labels when required shall be determined for each component documented on the single-line diagram.

An arc-flash risk assessment shall be mandatory for all new and existing power distribution systems including medium voltage and low voltage ELD projects.

If the stipulated level of PPE appears unsuitable to accomplish a particular task, the application of PPE and safety requirements for the workplace setting shall be studied and a recommendation provided.

Incident energy and arc ratings shall be calculated, and a determination of the PPE and labels when required made. The designer should make and document all attempts to reduce incident energy levels to below dangerous for all FAA distribution equipment. In the event that any equipment is still considered dangerous a remote operator should be considered. The calculations shall reflect the most current requirements set forth by the following:

• NFPA 70®, National Electrical Code

• IEEE 1584™. IEEE Guide for Performing Arc-Flash Hazard Calculations

• NFPA 70E®, Standard for Electrical Safety in the Workplace

Arc flash hazard studies shall be conducted during the design phase of the power distribution project. Findings shall be the basis for modifying the system to make it safer, and "engineer-out" hazards.

The following points are recommendations for implementing of an Arc Flash study in an existing facility:

a. Arc flash studies shall be conducted in existing facilities and shall be updated every 5 years or if the system has been modified.

b. Hardware changes often cannot be accomplished quickly due to the need for budget planning. An Approach for more complex hardware changes (such as circuit breaker replacements) is outlined below:

(1) Review the study and accept or reject the recommendations. Some recommendations (such as circuit breaker setting changes) can be readily accomplished; others cannot and will require more planning (such as circuit breaker replacements) and funding source identification.

(2) Before changes are implemented, any necessary safety risk assessments will be performed. The assessment should include approved written procedures ensure mitigating risk to the NAS during changes to circuit breakers and settings, including returning to original conditions.

(3) If possible, test the recommended circuit breaker settings onsite prior to finalizing the study and printing labels.

(4) The study is finalized and labels are printed.

(5) Draft modification documents, Technical Instruction changes, and handbook changes are created when applicable.

(6) Modifications are issued if necessary and the trip to the site is planned.

2-7

(7) The site is modified and operational testing is performed.

(8) Labels are applied to equipment.

(9) Feedback is provided on the testing results and any missing or incorrect labels. If necessary the study is updated and labels are reprinted.

2-8

Chapter 3. Determining the Need for a Study

This chapter provides guidance on determining who, when, and to what extent or level, a SCA, PDCA, or AFRA is needed. Figure 1, the Calculations Decision Process Flowchart, provides an overview of this decision process.

The calculation decision process starts with an assessment by a qualified engineer, who, in consultation with Engineering Services, the District/System Support Center (SSC) manager, EOSH, and/or Program manager (s) as appropriate, will determine if there is a need to conduct full analysis and calculations. The assessment process can take place in the planning or design phase, and will be documented.

The engineer shall assess the project and shall consider factors such as: modifications that lead to changes of short circuit currents, changes of protective devices coordination, or changes of incident energy. These modifications include, but are not limited to, (1) increasing or decreasing the capacity of a transformer or an engine generator (EG); (2) changing type or model of circuit breaker; (3) modifying settings of a circuit breaker; (4) considerable change of conductors either by increase or reduction of size and /or length; (5) addition of sources of alternative of energy;

(6) changing settings of E/G control in such a way that it results in increase of incident energy;

and (7) modification of topology; or (8) addition of 50 HP motors or larger. Details concerning each of these modifications are contained in this chapter. The assessment process also shall consider lack of existing calculations, and or outdated calculations (more than 5 years old).

An accurate determination of short-circuit currents is necessary for proper sizing and selection of electrical equipment such as switchgear, switchboards, panelboards, OCPDs, and disconnects.

Post-installation modifications to the utility transformer, facility load and power distribution system may change the short-circuit currents. These changes may require that the SCA be redone, to verify the adequacy of the existing system and/or indicate where the existing system is now inadequate.

The scope of the study for projects such as Uninterruptible Power Supply (UPS) systems and EGs retrofits shall includefrom the service entrance to the equipment serviced by replacement.

During the assessment process the data required to conduct the study as well as the practical operating scenarios shall be determined.

The generally accepted methods of determining Incident Energy and PPE are ultimately based on short-circuit current and clearing time. Modifications to the facility load and/or power distribution system, including circuit breaker or protective relay setting changes, may also impact the AFRA.

In the event that the site, district, service area, Power Services Group, and/or program office cannot agree upon the level of study required, the issue will be elevated to Technical Operations for resolution.

3-1

Figure 2. Calculations Decision Process Flowchart

In accordance with Chapter 3 of the Order, Qualified Engineer in consultation with Engineering Services, the SSC/District manager, and/or Program manager(s) as appropriate will conduct an assessment of the project as early as practically possible in the design phase, and will determine if there is a need to conduct complete calculations.

Yes

Conduct SCA, PDCA, AFRA, and other calculations as required.

No Proceed with project

3-2

Chapter 4. Coordination Guidelines

Selective coordination is both an art and a science. A perfectly coordinated system can not 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 goals: (1) Protection of people and equipment; (2) Continuity of service. The following guidelines will assist in the process:

1. Minimize the number of protective devices between the main service disconnect and the branch circuit breaker of any particular load. The elimination of main breakers at branch panel boards will assist in this process. However, in all cases a coordinated electrical system must comply with the NEC.

2. Consider using larger ampere frame circuit breakers to facilitate proper coordination.

Ensure that available space limitations can accommodate physical circuit breaker sizes.

3. Consider the use of electronic programmable type circuit breakers.

4. Use the protective device coordination study to design a coordinated distribution system.

5. Use national standard designs as indicated in the Critical Power Distribution System Program Implementation Plan (P6980.00) wherever possible.

6. Verify short circuit ratings of components used in the electrical distribution systems are adequate for the application.

7. Elevators shall be coordinated in accordance with the NEC.

8. Examination of the load's power continuity requirements shall be taken into account. As an example, if an interruption in a chiller motor on the essential bus of a manned facility will not affect the NAS, coordination may have less stringent requirements. If the power feeds equipment that directly controls the landing of airplanes, coordination must be followed to the extent possible.

9. When difficulty is encountered consult with appropriate regional or national authorities.

10. Protection of people and equipment must always be accomplished. Protection is not to be compromised to obtain coordination.

11. In instances of unmanned facilities where substantial time may elapse before a loss of power is identified, coordination is required.

12. Ground fault protection should be accomplished for circuits in accordance with the NEC.

In these cases, the ground fault system should have a separate coordination study and analysis performed.

13. Power distribution system protective devices should coordinate to a level such that no conductor, device, or circuit not directly critical to the safety or function of Air Traffic systems, should ever cause or allow an interruption in service to any device or circuit necessary for the safety or direction of Air Traffic.

14. Power distribution system protective devices should coordinate to a level such that a fault on the A bus of a dual redundant system will not disrupt or interfere with the operation of the B bus of the power system.

4-1 http:P6980.00

15. 100% selective coordination between the branch circuit breaker and the circuit breaker upstream, such as the panel main circuit breaker, is a must.

16. Ensure selective coordination in the path to critical loads.

17. Comply with the appropriate NEC articles regarding coordination.

18. Dynamic impedance is an important concept in circuit breaker coordination and can be considered by selecting OCPD based on actual published test data from the device manufacturers.

19. Ensure that there is no penetration of the OCPD TCC curve to the feeder thermal curve in the instantaneous region.

20. Ensure that OCPD will not trip or clear due to inrush currents.

21. Ground fault protection may be used to detect and interrupt arcing fault currents.

22. Time-Current coordination, i.e. PDCA, must be based on accurate short-circuit current calculations.

23. While SCA and PDCA use only the maximum available utility short circuit current, the AFRA must consider both the maximum and minimum available utility short circuit current.

24. The electrical utility data shall be obtained very early in the design phase.

25. Set Short Time Delay I2t out/off whenever possible.

4-2

04/13/2016 6950.27A

Chapter 5. Administrative Information

5-1. Distribution. This order will be distributed electronically.

5-2. Background.The NEC defines coordination as "Localization of an overcurrent [i.e.

overload, short circuit, or ground fault] condition to restrict outages to the circuit or equipment affected, accomplished by the choice of OCPDs and their ratings or settings." Coordination starts with the load. A panel branch circuit breaker needs to coordinate with the panel main circuit breaker, to allow the other branch circuit equipment to remain operational should that one branch circuit develop an overload or fault. The switchboard branch circuit breaker upstream of that panel main may not need the same level of discrimination.

Several other NEC Articles and Paragraphs address additional requirements regarding coordination. These include but are not limited to: Paragraph 620.62 (Elevators); Paragraph

695.3 (Fire Pumps); Paragraph 700.27, (Emergency Systems); Paragraph 701.27 (Legally Required Standby Systems); and Article 708 (Critical Operations Power Systems).

The NEC requires that signs and/or labels shall be provided on all electrical equipment such as medium and low voltage switchgear, switchboards, panel boards, transformers, industrial control panels, meter sockets, motor control centers, standby/emergency generators, automatic transfer switches, Elevator Motor Controllers, Fire Pump Motor Controller and Automatic Transfer Switches, Chiller and other HVAC Power/VFD controllers as required. The NEC also requires labeling of service equipment with the maximum available fault current.

5-3. Definitions.

Form / Fit / Function replacement: Replacement of existing equipment with new equipment that has the same:

integral part of another item;

• Function, i.e., the action or actions that the equipment is designed to perform.

5-1

Appendix A

Appendix A. Power Systems Analyses and Calculations

This table summarizes the various types of analyses that are necessary for a properly designed power system.

Table 1. Power System Analysis and Purpose

Type of Analysis / Calculation Load Analysis: Designer shall use actual load whenever possible, Designer shall use already existing load data studies such as the Jacobs Study of May 25, 2012, "Facility Power Load Analysis", and shall consider load profile, demand factors, and diversity factors, designer shall consider similar actual loads from similar existing facilities if actual loads are not available, designer shall use name plate data if no actual load data are available. Load analysis shall be submitted at the 35% deliverable, and shall be updated with every deliverable.

Load Flow: Designer shall conduct a load flow calculations, using the load data and topology, and shall provide the load flow calculations as a part of the 35% deliverable, and shall update this calculations for every submission.

Voltage Drop: Designer shall conduct voltage drop calculations, special attention shall be paid for low voltage long run circuits serving remote panels or remotely distributed loads. Voltage drop calculations shall be submitted in the 35% deliverable and shall be updated and submitted with each subsequent submission.

Conduit Fill: Designer shall conduct conduit fill calculations in low voltage circuits and shall confirm compliance with NEC rules, including derating factors.

Purpose This is the base for all calculations, and careful collection of data, verification, and documentation is required during the initial planning stage of the project and during initial survey.

This calculation shall be the basis for sizing conductors and shall be modified by the voltage drop calculations. The load flow study shall also serve as the basis for sizing circuit breakers and fuses, and shall be the basis for the long time pick up current setting of electronic circuit breaker and the thermal setting in the thermal magnetic circuit breakers in the Protective Device Coordination Analysis.

This calculation shall be the basis for sizing conductors in long run circuits.

This calculation shall be the basis for sizing conduits in low voltage distribution.

A-1

Table 1. Power System Analysis and Purpose (continued)

Type of Analysis / Calculation Short Circuit: Desianer shall conduct short circuit calculations and submit it with the 70% deliverable.

Designer shall conduct short circuit calculations based on the utility available maximum short circuit currents.

The short circuit calculations shall be updated with the following deliverables (90%, final, and the released for construction deliverable. The short circuit calculations shall be verified by the constructor of the system and modified if necessary. Designer shall use the short circuit current as basis for both (1) Sizing the circuit breakers; and (2) Selecting circuit breakers. Designer shall consider the dynamic impedance in selecting circuit breakers by means of selecting circuit breakers from manufacturer's published data for tested circuit breakers and the actual selectivity level ( Designer shall contact Power Services Group - System engineering if they need clarification). Designer shall attempt to reduce short circuit currents if he needs to do so.

Protective Device Coordination Analysis: Designer shall conduct a time current study on the protective devices in the topology under consideration. Designer shall submit the first time current study at the 90% deliverable and shall upgrade the study for the following submissions including the released for construction submission. Designer shall use both (1) The graphical method; and (2) Manufacturer's published data {time current curves and tested circuit breakers tables}. Designer shall show the following data as a minimum: Decrement curves of electrical generators, damage curves of equipment, In rush currents, Starting currents, short circuit currents, full load currents, settings of circuit breakers, protective device data, portions of the topology associated with the graphical method. Designer should limit number of protective devices to 4 devices on one graph. The time current coordination study shall be verified by the constructor of the system and shall be modified if the constructor used hardware different from the hardware used in the design.

Purpose The calculations based on the utility maximum available short circuit current shall be the basis for the sizing of the circuit breakers and the time current coordination. Both the minimum and maximum short circuit calculations shall be the basis for the arc flash calculation. The short circuit current calculations shall be the basis for setting the short time pick up, and the instantaneous settings in the time current coordination and the magnetic setting in the thermal-magnetic circuit breaker.

Time current coordination shall be based on the short circuit calculations. Time current coordination shall be an input to the arc flash calculations and shall be modified (if necessary) to reduce the incident energy. The study shall ensure achieving the following goals: (1) Protection of people and equipment;

and (2) Continuity of services. The settings of protective devices are a major output of the time current coordination study. One hundred percent (100%) selectivity is required between downstream circuit breakers protecting the load feeders and the circuit breaker directly above it; however 100% selectivity is not required as we move upstream (towards the power source). Achieving a balance between reduction of incident energy and selectivity shall be required.

A-2

Table 1. Power System Analysis and Purpose (continued)

Type of Analysis / Calculation Arc Flash Calculations: Desianer/ Investiaator shall conduct arc flash calculations and shall submit it with the 90% deliverable. Designer/ Investigator shall upgrade the arc flash calculations and submit it with the following deliverables including the released for construction deliverables. The Designer/ Investigator shall comply with NFPA 70E in its entirety including the informative annexes, and shall comply with IEEE 1584™. The Designer shall consult with appropriate EOSH organization, facility personnel, and Power Services Groups operations and maintenance teams in determining the need for conducting detailed calculations and determining the operating scenarios to include in the calculations.

Purpose The purpose of the arc flash study is several folds: (1) Identify inadequate protective devices; (2) Estimate incident energy at every bus; (3) Provide recommendations to reduction of incident energy; (4) Production of warning labels; and (5) Recommendations of Personal Protective Equipment. The arc flash calculations are based on short circuit calculations and time current coordination and the relationship between the three types of calculations are intertwined, designer may have to loop back in the design process in an attempt to reduce the incident energy by reduction of short circuit currents, protective devices settings, protective devices types, modifying of topology, and/ or recommending hardware.

A-3

04/13/2016 6950.27A

The various power systems calculations and analyses described above are a part of the project life, not only the initial design. The table below helps identify when each is required.

Table 2. Power System Analysis and Project Phase

Planning & Design

CD

Oo £ O O OCO CD 3 w

SOW addresses the calculations submittals and identifies them.

Drawings upgraded and submitted, and Calculations conducted, upgraded, and submitted with every stage of the project as agreed upon in the statement of work. *

100%.

Calculations reflect the contents of the One Line

Diagram and the electrical layout of equipment.

Recommended:

Collect data during initial survey.

Construction &

Commissioning

Construction Commissioning

Design calculations verified and/or updated to reflect actual installed hardware and circuit breakers including cable length and size.

Circuit breakers settings verified during commissioning.

Labels per JO 3900.64 produced and affixed to affected electrical equipment.

PPE ordered.

Necessary performance testing conducted, including ground-fault performance test as per National Electric Code Article 230, Paragraph 230.95(C)**

Operations &

Maintenance

Operations and

Maintenance procedures

Calculations updated every 5 years or as required to reflect the changes in electrical circuits and or available power from utilities.

Facilities keep an updated As Built One Line Diagram and electrical layout of equipment.

Labels per JO 3900.64 upgraded.

PPE upgraded.

* See Appendix D FPPS Data System ** Based on NFPA 70™, 2011 Edition. User shall use the latest edition.

A-4

Appendix B

Appendix B. Setting Circuit Breakers

The Time-Current Characteristic Curves shown in this appendix are general curves for the Thermal-Magnetic Trip Units and Electronic Trip Units. The separate curves show in general terms the effect of changing the various adjustments, pickups, and delay settings. The adjustments, pickups, and delays shown on the curves are not necessarily identical to actual adjustments, pickups, delays on field equipment. Time-current characteristic curves for specific circuit breakers are to be used when setting circuit breakers in the field.

B-1. Circuit Breaker Settings - Thermal-Magnetic Trip Units

Figure B-1. Typical Time-Current Characteristic Curve for Thermal-Magnetic Trip Unit i

^ Light over load trip here after long time a(li,t,)

\ >— Heavy over load trip here after short time b(b,fc) E i -y— Short Circuit trip here after short time y / (Instantaneous Trip)

'—Trip lime Independent of Current

/ Current i-— Rated Current (Ir)

B-1

Figure B-2. Typical Time-Current Characteristic Curve for Thermal-Magnetic Trip Unit showing effect of Thermal Adjustment

I i

Thermal adjustment range 0 *> 0. 75 1 from 0.5 to 1

- 6 — —9«~ lr 075 l ify xln

E

Current / / /r1=0.5xln— ' / 1

Ir2 = 0.75xln—' /

Ir3 = 10xln—'

B-2

Figure B-3. Typical Time-Current Characteristic Curve for Thermal-Magnetic Trip Unit showing effect of Magnetic Adjustment

Magnetic adjustment range from 5 to 10

Im ** ttj:

xln i F

Currer Im1 = 5xln - ^ / / / Im2 = 6 x l n ^ / / \

Im3 = 7 . 5 x l n ^ / / Im4 = 8.5xlrt^ /

Im5=10xln-J

B-3

B-2. Circuit Breaker Settings - Electronic Trip Units

Some models provide only Long Time/Short Time/Instantaneous (LSI) selective protection, with display.

Some models also include ground-fault protection for equipment in addition to selective protection (LSIG), with display.

Figure B-4. Typical Time-Current Characteristic Curve for Electronic Trip Unit

Time-Current Characteristic Curve

10000 T

J + +

CONTINUOUS CURRENT

LONG TIME DELAY

ftSLOPE

SHORT TIME •/,*

4!

PICKUP ****

-5 »—< U

'SHORT TIME PRAY Jt ft SLOPE

01 =•

» , » • * INSTANTANEOUS

PICKUP

0 01 SHORT TIME

DELAY PICKUP

0 001 11 u i 1- H 1 1—I I M i l l 1 1—I I I I

01 1 10 100 1000

Multiples of Current Rating

B-4

Long-Time Protection

Long-time protection is 11IDMT (Inverse Definite Minimum Time):

• Incorporates the thermal image function.

• Is set with the Ir pickup and the tr trip time delay.

Long-time Pickup (Ir pickup)

This is the magnitude of current that a circuit breaker can carry without tripping. Ir is a percentage of the circuit breaker nominal rating (In). Adjustment of this setting will vary the continuous current from about 20% to 100% of the circuit breaker nominal rating (I„).

Figure B-5. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Long Time Pickup Adjustment

8* s

Multiples ef Circuit Breaker Continuous Current Rating

B-5

Long-time Delay (tr trip time delay)

Long-time delay causes the breaker to wait a certain amount of time to allow temporary inrush currents, such as starting a motor, to flow without tripping.

Usually, the time adjustment is on a multiple of the continuous current rating (Ir). A common setting 6 x Ir as most motors draw current 6 times its full load current during starting. The setting depends on the motor driven load. The unit adjustment for this setting is seconds. The long-time delay effects the position of an I2t slope which means that lower levels of continuous current setting will allow the circuit breaker to remain online for longer periods of time.

Figure B-6. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Long Time Delay Adjustment

Long Sees @ 12 20

Z7'A I

L Mulfiplss of Circuit Blister Contiiwofls Currant Bating

B-6

Short-Time Protection

Short-time protection is definite time:

• Incorporates the possibility of an I2t inverse time curve function

• Is set using the ISd pickup and the tscj trip time delay

Short-time Pickup

Short-time pickup is used for discrimination or selective tripping. The short-time pickup function determines the amount of current the circuit breaker will carry for a short period of time, allowing downstream protective devices to clear short-circuits without tripping the upstream device. If this function is set to "OFF" position, the short-time pickup and short-time delay will be disabled.

Figure B-7. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Short Time Pickup Adjustment

Short Tim© Pickup 4 6 xlr 3

%m » 7 * k 1.S

Off 1C

.5 i=

Multiples of Circuit Breaker Continuous Current Rating

B-7

04/13/2016 6950.27A

Short-time Delay

Short-time delay, used in conjunction with short-time pickup, controls the time duration before a short-time pickup trip.

There are two modes:

• Fixed time - A fixed instantaneous trip point trips the breaker automatically and overrides any pre-programmed settings.

• I2t ramp - The I2t ramp mode is adjustable providing a short inverse time ramp. This allows better coordination with downstream thermal-magnetic circuit breakers and fuses.

Figure B-8. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Short Time Delay Adjustment

Short Time Delay Sees. .3 ,5

.45 t*m

. 1 - ».3I |2t

.06' Delay m\m @8xlr.18 .22

Fixad Tim© Settings

A |2T

Ramp

Multiples of Circuit Breaker Continuous Current Rating

B-8

Instantaneous Protection

Instantaneous Pickup

Instantaneous protection is definite time, set as I; pickup and without time delay.

Instantaneous Pickup is used to trip the circuit breaker with no intentional delay at any current between 2 and 40 times the breaker's continuous ampere setting (Ir).

Figure B-9. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Instantaneous Pickup Adjustment m M t-

MdtiplBs of Circuit Breslwr Continuous Zwmt Rating

B-9 i

Appendix B

Ground Fault Protection

Ground fault Pickup and Delay

Figure B-10. Typical Time-Current Characteristic Curve for Electronic Trip Unit showing effect of Ground Fault Pickup and Delay Adjustments ui Ground-fault HI Ground-fault Delay = Ground-fault Delay ""** Pickup s (PtOUT)ort=k H

( I , , N ) $

L ^ — Current Sensor or (IxS)

Fraction of Sensor Current(S)

B-10

Appendix C

Appendix C. Projects Requiring SCA and AFRA.

The following items address typical factors that affect the level of analysis or assessment, and the need for calculations.

Modification: Motor loads greater/equal to 50 HP using (1) direct-on-line/across the line starters; (2) starters such as reduced voltage starters, VFDs, soft starters, and smart controllers, any of which equipped with a bypass. This includes (a) single motor 50HP or greater; (b) multiple motors totaling 50HP or greater (Modeled as one larger motor).

Applies to the following situations:

a. Addition of new equipment.

b. Form / Fit / Function replacement. See Calculations Decision Process Flow Chart.

Modification: Power panels. There are special considerations for panels that are remote, i.e., are some distance from the upstream protective device.

• Feeder circuit breakers protecting long distance feeders may not be able to sense a fault far enough from the circuit breaker due to the attenuation of the short circuit…