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World Safety Conference Expo presentation

World Safety Conference Expo presentation

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Nfpa Wsc&E 080602 Presentation Transcript

  • 1. Emergency Power System Selective Coordination NFPA 2008 World Safety Conference & Exposition Monday, June 2, 2008
  • 2.
    • Douglas R. Strang, Jr., P.E.
    • BTEE, MEng
    • Licensed Professional Engineer in NY, NJ, & PA
    • Active member of IEEE, NETA, & IAEI
    • Electrician for several years before engineering
    • President of S & S ENGINEERING, P.C.
    • Specialized in power system studies
      • Fault current analysis
      • OCPD coordination
      • Arc flash hazard analysis
      • Forensic investigation
    Emergency Power System Selective Coordination
  • 3.
    • Outline:
    • What is Selective Coordination?
    • Why is Selective Coordination important?
    • What are some of the challenges?
      • Protection vs. Selectivity
      • Overload vs. Fault
      • Phase vs. Ground Fault Protection
      • Utility vs. Generator Source
    • Examples
    • Coordination Methods
      • Fusible system
      • Circuit breaker system
      • Zone Selective Interlocking (ZSI)
    • Parallel generators
    • Points to remember
    Emergency Power System Selective Coordination
  • 4. Emergency Power System Selective Coordination What is Selective Coordination?
  • 5. N.E.C. Definition: Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings. Emergency Power System Selective Coordination What is Selective Coordination? The Goal: To isolate the faulted portion of the electrical system quickly while at the same time maintaining power to the remainder of the electrical system .
    • Protect equipment
    • Minimize power outages (size & severity)
  • 6. Emergency Power System Selective Coordination What is Selective Coordination? Without Selective Coordination With Selective Coordination OPENS NOT AFFECTED UNNECESSARY POWER LOSS OPENS NOT AFFECTED Fault Fault
  • 7.
    • N.E.C. Articles:
    • 230.95 GFP of Equipment. FPN No. 2. (Services)
    • 240.12 Electrical System Coordination. (Overcurrent Protection)
    • 517.26 Application of Other Articles. (Health Care Facilities)
    • 620.62 Selective Coordination. (Elevators…)
    • 700.27 Coordination. (Emergency Systems)
    • 701.18 Coordination. (Legally Required Standby Systems)
    • 708.54 Coordination. (Critical Operations Power Systems [COPS])
    Emergency Power System Selective Coordination Why is Selective Coordination Important?
  • 8. Emergency Power System Selective Coordination A Brief History Lesson
    • 1971 NEC Articles
      • 230 Services (Ground-Fault Protection of Equipment)
    • 1993 NEC Articles
      • 620 Elevator Circuits
    • 2005 NEC Articles
      • 700 Emergency Systems
      • 701 Legally Required Standby Systems
      • 517 Healthcare Facilities
    • 2008 NEC Articles
      • 708 Critical Operations Power Systems
  • 9.
    • Life Safety – protect the public health and welfare
    • Life Safety Operations – ensure continuous power to vital loads, even during times of emergency such as fire, flood, earthquake, etc.
    • Evacuation & Rescue Operations – ensure operation of critical systems such as communications, egress lighting, fire pumps, and smoke removal equipment
    Emergency Power System Selective Coordination Why is Selective Coordination Important?
    • Why Emergency & Legally Required Standby Systems?
    • Emergency Systems – “…those systems legally required and classed as emergency by municipal, state, federal, or other codes, or by any governmental agency having jurisdiction.”
  • 10. System Protection vs. Selectivity An Overcurrent Protective Device Coordination Study evaluates the selection of devices and determines proper settings and ratings for protection AND selectivity Emergency Power System Selective Coordination What are some of the challenges? Protection : To disconnect faulted equipment from the system BEFORE damage occurs [requires FAST and SENSITIVE tripping] Selectivity : Requires some devices employ TIME DELAY tripping or HIGHER activation (pickup) levels [Time delays are dependent on location in system] Can be contradicting objectives
  • 11.
    • System Protection vs. Selectivity
    • Because of the application specific variables involved, an OCPD Coordination Study is as much an art as it is a science
    • Complete selective coordination can be very difficult, if not impossible, to achieve if not addressed in the system design phase
    Emergency Power System Selective Coordination What are some of the challenges?
  • 12. Overload vs. Fault Emergency Power System Selective Coordination What are some of the challenges? Overload – operation of equip in excess of normal, full load rating, or ampacity of conductor causing damage or dangerous overheating Typical range: 101% < I < 250% full load rating Fault – an unintentional and undesirable conducting path in an electrical power system. Can take many forms; 3L, 3i0, LL, LL-G, L-G Typical range: I > 250% full load rating
  • 13. Phase vs. Ground Fault Emergency Power System Selective Coordination What are some of the challenges? Phase Protection : OL or OC, LL faults, 3ph faults, usually of higher current levels GF Protection : L-G faults, LL-G, 3ph-G faults GFP: (Art. 100) – system intended to provide protection of equipment from damaging L-G fault currents by disconnecting all ungrounded conductors of faulted circuit A B C SLG L-L 3ph
  • 14. Emergency Power System Selective Coordination What are some of the challenges?
    • Utility vs. Generator Source
    • An OCPD Coordination Study must address BOTH sources
    • The idea is not to depend on the alternative power source (i.e. emergency power system) unless there is a loss of normal power
    • N.E.C. 700.27 Coordination .
    • Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. (There are 2 exceptions)
  • 15. Emergency Power System Selective Coordination What are some of the challenges? ATS Emergency Source N E Normal Source Panel ATS Emergency Source N E Normal Source Panel
  • 16. Emergency Power System Selective Coordination Example 1
    • Consequences
    • Non-coordinated OCPDs
    OCPD Opens OCPD not affected ATS Emergency Source N E Normal Source Panel Fault
    • No transfer activated
    • Unnecessary outage
  • 17. Emergency Power System Selective Coordination ATS Emergency Source N E Normal Source
    • Consequences
    • Non-coordinated OCPD's
    OCPD Opens OCPD not affected Panel Fault
    • Reliability concerns whether generator or transfer equipment operate properly Why increase possibility of unwanted outcome?
    • Unnecessary blackout persists (hatched)
    • Transfer activated
    • Blackout all emergency loads temporarily (shaded)
    Example 2
  • 18. Emergency Power System Selective Coordination The Two Exceptions Exception 2: Two devices of same amp rating in series Exception 1 : Transformer primary and secondary Same Circuit Neither exception reduced life-safety because no additional parts of the electrical system would be shut down unnecessarily Hashed OCPDs do not have to be selectively coordinated Same Circuit 400A OCPD 400A OCPD
  • 19. Emergency Power System Selective Coordination Coordination Methods
    • Fuses
    • Each fuse manufacturer has conducted fuse testing and analysis to develop a simple fuse type/ampere ratio method to select fuses that are selectively coordinated
    • Includes all overcurrent levels up to the fuses’ interrupting ratings (up to 200 kA), including the sub-cycle region
    • Based on:
      • Fuse types lineside and loadside
      • Meeting at least minimum ampere rating ratio between lineside/loadside fuses
  • 20. Emergency Power System Selective Coordination Coordination Methods No plotting required Line Side Fuse Load Side Fuse
  • 21. Emergency Power System Selective Coordination Coordination Methods
    • Fuses
    • Branch circuit panelboards are available using class CC fuses for typical 15, 20, and 30 A branch circuits
    • Full selective coordination is achieved for the full range of fault current as long as the selectivity ratio guide is followed
    • Note the TCC is only useful for overcurrents represented by the fuse curve shown on plot. Not applicable for Isc greater than arrow
  • 22. Emergency Power System Selective Coordination Coordination Methods
    • Fuses - Summary
    • Use fuse manufacturer’s Selectivity Ratio Tables which are valid up to 200kA (the fuses’ interrupting ratings)
      • If ratios are not satisfied, investigate another fuse type or design change
    • Every fuse manufacturer’s ratios apply only to their fuses
      • Do not mix fuses of different manufacturers in system
    • Contractors & maintenance personnel must install fuses per plans
    • Life-cycle considerations:
      • Ensure proper spares are readily available
      • System and fault current changes over time will not affect selective coordination when ratios are used
      • Periodic maintenance of fuses is not required, but check terminations & switches with IR scan
  • 23. Emergency Power System Selective Coordination Coordination Methods
    • Circuit Breakers
    • Investigate different types based on available fault current and required trip functions:
      • MCCB
      • ICCB
      • LVPCB
    • Instantaneous trip (IT)
    • Fixed high magnetic IT
    • Short time delay (STD) w/ IT override (MCCB/ICCB)
    • Short time delay (STD) w/o IT override (LVPCB)
  • 24. Emergency Power System Selective Coordination Coordination Methods Up to where the circuit breakers cross, it is interpreted to be coordinated. See 800A 200A 30A Up to 7600A Up to 1500A X X 1500A 7600A 30A 0.01s 0.1s 800A IT = 10X 200A IT = 10X Circuit Breakers
  • 25. Emergency Power System Selective Coordination Coordination Methods Illustrates two instantaneous trip MCCBs: Lineside: 400A (7X IT) Loadside: 100A (Fixed IT) Where they intersect is point of non-coordination 0.01 seconds typically lowest time on TCCs CB IT unlatching times are less than 0.01s Circuit Breakers 0.1s 0.01s 0.001s
  • 26. Emergency Power System Selective Coordination Coordination Methods Interpret CB curves: 800A CB does not coordinate with the 200A CB above 5400A, even though the curves do not cross on the plot. 2250A 5400A 800A 30A 200A 0.01s 0.1s 800A 200A 30A Up to 5400A Up to 2250A X X Circuit Breakers
  • 27. Emergency Power System Selective Coordination Coordination Methods Circuit Breakers
  • 28. Emergency Power System Selective Coordination Coordination Methods Circuit Breakers 1500A Crossing Point Interpreting Curves Max. 2700A: CB Mfg. Coordination Testing CB Manufacturer’s Coordination Tables can help show coordination for higher fault current than simply plotting curves Example: 30A & 200A MCCBs 800A 30A 200A 0.01s 0.1s
  • 29. Emergency Power System Selective Coordination Coordination Methods Circuit Breakers Selective coordination for all overcurrents up to the interrupting rating for each circuit breaker Still need to plot curves to ensure there is no crossing of circuit breaker curves. Must have time settings with enough separation. 800A 30A 200A 0.01s 0.1s
  • 30. Emergency Power System Selective Coordination Coordination Methods Circuit Breakers - ZSI 1 2 3 X Fault Here 3 2 1 1200A 175A 400A 0.01s 0.1s CB3 Trips Instantaneously Restraint signal Restraint signal
  • 31. Fault Here Emergency Power System Selective Coordination Coordination Methods Circuit Breakers - ZSI 1 2 3 X No signal Restraint signal CB2 Trips Instantaneously 3 2 1 1200A 175A 400A 0.01s 0.1s
  • 32. Emergency Power System Selective Coordination Coordination Methods
    • Tested coordination tables for some CB to CB combinations
    • Wide range of interrupting ratings (many models)
    • MCCBs, ICCBs, LVPCBs
      • Different options available for each type
      • Different range of settings available
    • Use larger frame or more sophisticated CBs to achieve selective coordination for higher available fault currents
    • Coordination can be achieved with standard molded case, thermal-magnetic circuit breakers if the fault current is just right
    • ZSI will not make a system coordinate , but can provide better protection for a coordinated system using short-time delays
    Circuit Breakers - Summary
  • 33. Emergency Power System Selective Coordination Coordination Methods Parallel Generators
    • Typical of hospitals or large data centers
    • Fault current available can be as much as the utility or greater
    • Available fault current will vary with the number of generators on line
    • Fault and coordination study must address different modes of operation
    • Plot generator decrement curve for each number of generators on line
      • Verify enough fault current to activate overcurrent devices
  • 34. Emergency Power System Selective Coordination Coordination Methods Parallel Generators
  • 35. Overload protection only. Coordinates with overload characteristics of downstream OCPDs Emergency Power System Selective Coordination Coordination Methods Parallel Generators Normal Source N E N E N E G 87B G Bus differential relaying provides short-circuit protection for bus & generators for bus fault (between CTs) Fuses or CBs selectively coordinated with downstream OCPDs for all overcurrents Emergency Source Bus Differential Relay
  • 36. Emergency Power System Selective Coordination
    • Points to Remember
    • Complete selective coordination can be achieved with circuit breakers or fuses, if addressed during the system design phase – No one size fits all solution
    • Plan on an increased project cost, whether for stocking spare fuses or for more extravagant circuit breakers
    • Be aware of the typical thermal-magnetic, molded case circuit breaker TCC overlap in the instantaneous trip region
    • Consider how to apply required ground fault protection when using a fusible system
    • Consider main lug only (MLO) panelboards in the design to provide a fault current differential between OCPD’s
  • 37. Emergency Power System Selective Coordination
    • Points to Remember
    • Consider zone selective interlocking (ZSI) of circuit breakers in series if short-time delays are employed
    • Use manufacturer’s selectivity guides (for both c.b.’s and fuses) to ensure coordination in the sub-cycle region (< 0.01 sec) not typically captured by analysis software
    • Analyze with actual generator alternator sub-transient reactance and X/R ratio. Pay attention to excitation method and decrement curve.
    • Know that selective coordination is a Code requirement for life safety , and is not optional for emergency and legally required standby systems
  • 38. Thank you! www.sandsengineering.com Contact : Douglas R. Strang, Jr., P.E. PO Box 345 Batavia, NY 14021-0345 585-235-3530 [email_address] [email_address] Emergency Power System Selective Coordination