FEMA P-1019, Emergency Power Systems for Critical Facilities: A Best Practices Approach to Improving Reliability (September 2014)

Overview

The guide examines why emergency and standby power systems fail during and after natural hazards and how to prevent it. It first explains the NEC and NFPA categories: emergency systems, legally required standby systems, optional standby systems and critical operations power systems. Under the NEC, an emergency system needs an automatic transfer switch that moves load within 10 seconds of loss of normal power; legally required standby systems must transfer within 60 seconds, and optional standby systems have no timed transfer requirement.

The second chapter describes how winter storms, high winds, floods and earthquakes affect power lines and building systems, with case studies such as the 2007 winter storms, the 2011 tornadoes, the June 2012 derecho winds, Superstorm Sandy and the 1994 Northridge earthquake. Chapters 3 and 4 cover deciding whether a facility is critical, emergency preparedness and a detailed assessment of needs: life-safety equipment, fire pumps, lighting, mechanical equipment and other building systems.

Chapter 5 compares sources. Battery systems typically give about 5 minutes of ride-through when backed by generators and up to 2 hours for life-safety loads without a generator; data centers and telco offices may design for 24 hours or more. Flywheel systems provide 1 minute or less, enough for generators to start and take load (typically about 10 seconds). Generators over 300 kW are almost exclusively diesel. NFPA 110 requires onsite fuel for full-load operation of 5 minutes to 48 hours (typically at least 90 minutes); high-seismicity critical facilities need 96 hours, and FEMA 543 also recommends 96 hours of run time without refueling.

Chapter 6 treats holistic design, layout and hazard mitigation. For flooding it recommends protecting critical facilities to the greatest of BFE plus 2 feet, the local DFE and the 500-year flood elevation, and emergency power systems to the greatest of BFE plus 3 feet, local DFE plus 1 foot and the 500-year elevation plus 1 foot. Elevation is preferred to dry floodproofing because once water overtops the protection equipment is inundated quickly. Seismic anchorage, fuel tank and piping protection, and selective coordination (the protective device nearest a fault opens first) are also covered.

Chapter 7 covers optional standby power in existing facilities: identifying critical loads, reconfiguring distribution and connecting through the electrical service. Appendix C addresses generator sizing: use demand and diversity factors that represent emergency operation and choose step voltage and frequency dips. The guide is not a data center standard and rests on U.S. codes, but it offers directly applicable checkpoints for generator plants, fuel storage and distribution resilience.

Key points

1. NEC emergency systems require an automatic transfer switch that transfers load within 10 seconds of loss of normal power.
2. NEC legally required standby systems must transfer load within 60 seconds of loss of normal power; optional standby systems have no timed transfer requirement.
3. Batteries typically provide about 5 minutes of ride-through when backed by generators and up to 2 hours for life-safety loads without a generator; data centers and telco offices may design for 24 hours or more.
4. Flywheel systems provide 1 minute or less of emergency power, enough for generators to start and transfer load (typically about 10 seconds).
5. Generators over 300 kW are almost exclusively diesel-fueled.
6. NFPA 110 requires onsite fuel for full-load operation for between 5 minutes and 48 hours (typically at least 90 minutes); critical facilities in high-seismicity areas require 96 hours, and FEMA 543 also recommends 96 hours without refueling.
7. Emergency power systems in critical facilities should be protected to the highest of BFE + 3 ft, local DFE + 1 ft, or the 500-year flood elevation + 1 ft.
8. Critical facilities themselves should be protected to the greatest of BFE + 2 ft, the local DFE and the 500-year elevation; elevation is preferred over dry floodproofing.
9. Manufacturers commonly recommend continuous diesel generator loading of at least 30% of rated capacity to avoid wet stacking; oversizing beyond double the current load is not advised.
10. A 6% allowable frequency dip and a 20% voltage dip may be preferable to the 10% and 35% defaults some manufacturers list for sensitive electronic loads; tighter limits require a larger generator.

Using it in design

• At critical-facility data centers, place generators, ATS, fuel tanks and pumps above the greatest of BFE + 3 ft, DFE + 1 ft and 500-year elevation + 1 ft, and prefer elevation to dry floodproofing.
• Size onsite fuel volume for the target run time; NFPA 110 durations range from 5 minutes to 48 hours and reach 96 hours in high-seismicity areas. Check refueling access, protection of tanks and piping, and that fuel supply does not depend solely on the grid.
• When sizing generators, use separate demand and diversity factors for loads operating in an emergency, plan stepwise load application and set allowable voltage (for example 20%) and frequency (for example 6%) dips.
• Avoid generators sized beyond twice the current load and keep continuous loading at 30% or more of rated capacity; leave room in the generator room for added units, switchgear and synchronising gear for growth.
• Match UPS, battery and flywheel ride-through to generator start time and to the transfer requirements (10 seconds, 60 seconds), and justify battery runtime of 24 hours or more for a data center.
• Make selective coordination a design requirement for emergency distribution: the protective device nearest the fault must open, and a main breaker must not black out the whole facility.

Who should read it

Electrical engineers who design emergency and standby power for data centers or critical facilities, specifiers of generators and fuel systems, and resilience planners.

Document contents

1. Chapter 1 - Introduction
2. Emergency Power from a Code Perspective (Emergency, Legally Required Standby, Optional Standby, Critical Operations Power Systems)
3. Planning for Facility Resilience
4. Chapter 2 - Natural Hazard Effects on Power Systems (Winter Storms, High Winds, Flooding, Earthquakes, Other Events)
5. Chapter 3 - Critical Facilities and Emergency Preparedness
6. Chapter 4 - Determining Emergency Power Needs
7. Chapter 5 - Emergency Power Sources and Systems
8. Emergency Power Sources: Stored Energy Devices and Generators
9. Emergency Power Distribution and Optional Standby Generators
10. Electrical Control and Coordination: Selectivity and Coordination
11. Chapter 6 - Design Considerations for Emergency Power Systems in New Facilities
12. Layout, Location and Protection from Natural Hazards
13. Chapter 7 - Design Considerations for Optional Standby Power Systems in Existing Facilities
14. Appendix A - General Code Considerations for Emergency Power in Critical Facilities
15. Appendix B - Redundancy of Electrical Power Systems
16. Appendix C - Generator Sizing
17. Appendix D - Emergency Power System Operational Checklist
18. Appendix E - Examples of How to Utilize this Document

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Publication details

Authors

Applied Technology Council (ATC)

Publisher

FEMA

Year

2014

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