UFC 3-540-01 Engine-Driven Generator Systems for Prime and Standby Power Applications (1 August 2014, Change 3, 26 January 2023)

Overview

UFC 3-540-01 supersedes UFC 3-540-04N (16 January 2004); this copy includes Change 3 of 26 January 2023. It is mandatory for the design and installation of fossil-fuelled engine-driven generator systems at DoD installations, gives minimum design requirements and does not apply to tactical generators. Backup power design follows IEEE Std 446, and permanently installed systems comply with NFPA 110 emergency power supply system (EPSS) requirements, designated Class X where X is the required operating hours. The NFPA 70 Articles 700 (emergency), 701 (legally required), 702 (portable) and 708 (COPS) are distinguished. A remote manual stop station, a remote control and alarm panel and a remote common audible alarm to a 24-hour staffed location are required, each deletable with the activity's documented concurrence. Some provisions are Service-specific (Air Force, Army).

For fuel, diesel or jet fuel is the primary source where on-site storage is required; natural gas may be primary only where on-site storage is not required, and diesel/natural gas dual-fuel units are allowed (not for the Air Force). At least seven days of fuel is provided either in a dedicated on-site main tank or from a confirmed delivery source that can deliver reliably during long outages; if delivery meets the seven days, each generator set still needs a local tank of at least 24 hours at full-load consumption. Design analysis covers transient and steady-state loads, start-up, transformer inrush, motor starting and UPS loads, and a harmonic analysis is performed where switching power supplies make up 25 percent or more of the load.

The power rating category follows EGSA 101P for DoD facilities and ISO 8528-1 for host nation facilities; prime ratings typically allow a 10% overload for 1 hour in 12, and emergency standby ratings apply to up to 200 operating hours per year. Performance classes are defined by transient limits: for a 100% load step, frequency deviation within -10% (G2) or -7% (G3), voltage deviation within -20% (G2) or -15% (G3), and recovery times under 5 s and 6 s for G2 and under 3 s and 4 s for G3. Steady-state voltage regulation is within 2.5% for G2 and 1% for G3, and the frequency band within 1.5% and 0.5%. For G3 and G4 loads the designer of record must document system behaviour.

For the Air Force, generators are sized to exceed 50% of rated load using facility loads only, and whole-building generators are allowed only when the mission-essential load exceeds 70% of the facility load. Prime generators may serve varying loads without hour limits but the average load factor must not exceed 70% of the prime rating; where spinning reserve is required, multiple generators each run at no more than 50% load so one can pick up the whole load if another fails. Three-phase systems use four-pole devices and UL 1008-listed ATS to switch between sources. Paralleling follows the IEEE 1547 series and the utility's rules. Controls, starting (pneumatic up to 3 MW; electric for emergency and legally required units), DC power (two battery banks), black start and commissioning are covered.

UPS systems can have a detrimental effect on generator control systems. Per Appendix D, the design must address communication so the UPS knows it is on a generator, minimising allowed battery charging current while on generator (charging is not a critical load), power walk-in limiting the rate of transfer from battery to generator, and energising the UPS input filter only after adequate load is established. A UPS typically applies load gradually over 3 to 60 seconds, and an unloaded input filter can present a leading power factor beyond the generator's voltage control. Appendices give example one-line configurations, design checklists, generator sizing, portable generator connections and power plant considerations.

Key points

1. Generator sizing must account for transient and steady-state loads, start-up and UPS battery charging; for the Air Force, UPS charging load is sized for a float charge, not recharge from deep discharge.
2. At least seven days of fuel storage is required, on-site or from a confirmed delivery source; even with deliveries, each generator set needs a local tank of at least 24 hours at full-load consumption.
3. Harmonic analysis is required when switching power supplies make up 25% or more of the system load.
4. Prime ratings typically allow a 10% overload for 1 hour in 12; emergency standby ratings apply to up to 200 operating hours per year.
5. For a 100% load step, frequency deviation is within -10% (G2) or -7% (G3), voltage deviation within -20% (G2) or -15% (G3), with recovery under 5 s / 6 s for G2 and 3 s / 4 s for G3.
6. Steady-state voltage regulation is within 2.5% for G2 and 1% for G3; steady-state frequency band is within 1.5% and 0.5% respectively.
7. Air Force generators must be sized to exceed 50% of rated load using facility loads only; whole-building generators are allowed only when mission-essential load exceeds 70% of the facility load.
8. Prime generators may serve varying loads without hour limits, but average load factor must not exceed 70% of the prime rating.
9. Where spinning reserve is required, multiple generators run at no more than 50% load each, so one can pick up the whole load if another fails.
10. UPS integration needs generator-to-UPS communication, minimum battery charging on generator, power walk-in limiting and delayed energising of the UPS input filter.

Using it in design

• Include transient and steady-state loads, transformer inrush, motor starting and UPS load in the generator sizing study, and calculate UPS charging load using the minimum charging current allowed while on generator.
• Set fuel to seven days of mission-load consumption; if relying on delivery, verify the supplier's reliability in long outages and provide a 24-hour local tank per generator at full-load consumption.
• Choose the performance class (G2, G3, G4) from load sensitivity and write the 100% load-step frequency and voltage deviations and recovery times into the generator and UPS specification together; document system behaviour for G3 and G4.
• Run a harmonic analysis where switching power supplies are 25% or more of the load and carry the result into generator sizing.
• Test the leading-power-factor risk from the UPS input filter and 3-60 s walk-in during generator and UPS commissioning, and ensure the filter energises only after adequate load and the UPS detects generator operation.
• For paralleled generators needing spinning reserve, run each at no more than 50% load; check four-pole switching, UL 1008-listed ATS and IEEE 1547 requirements for paralleling.

Who should read it

Electrical and mechanical engineers who design standby and prime generator, fuel and ATS systems for data centres and mission-critical facilities, and commissioning teams.

Document contents

1. Introduction
2. Reissues and Cancels
3. Purpose and Scope
4. Applicability
5. General Building Requirements
6. EMI/EMP Protection Systems
7. Project Requirements
8. Mission Facility Support Requirements
9. Cybersecurity
10. Standby Power Generators Design Criteria
11. Applications (NFPA 110 and NFPA 70 compliance)
12. Authorized Fuel Types
13. Onsite Fuel Storage Capacity
14. Analysis Requirements (design analysis, environmental, seismic classification)
15. Utility Requirements for Paralleling
16. Power Rating Category
17. Performance Class Transient Limits
18. Design Criteria (circuit wiring, automatic operation, single generator sets, paralleling)
19. Prime Power Generator Design Criteria
20. Prime Power Generator Classification
21. Prime Power Generator Design (RAM, capacity factors, fuel, cooling, exhaust, starting, control, DC power, paralleling switchgear, black start)
22. Environmental
23. Commissioning
24. Generator Plant Security
25. Appendix A References
26. Appendix B Examples of System Configurations
27. Appendix C Design Checklist
28. Appendix D Generator Sizing (load evaluation, generator rating, UPS systems, power quality)
29. Appendix E Connection Methods for Portable Generators
30. Appendix F Facility Design Types
31. Appendix G Air Force Generator Authorizations
32. Appendix H Power Plant Considerations
33. Appendix I Glossary

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Publication details

Authors

Air Force Civil Engineer Center (AFCEC); U.S. Army Corps of Engineers (USACE); Naval Facilities Engineering Command (NAVFAC)

Publisher

U.S. DoD (UFC)

Year

2023

Document language

English

Source type

Government / public

Access

Open licence — downloadable

Licence

U.S. public domain — U.S. Government work; free to reuse

Licence evidence

www.copyright.gov

Citation