Slide 1: Arc Flash and Selective Coordination
PowerHour webinar series for consulting engineers Experts you trust. Excellence you count on. Arc Flash and Selective Coordination Wednesday June 8 1:00 CDT / 2:00 EDT (1PDH issued by Cummins)
Slide 2: Welcome!
Welcome! PowerHour is designed to help our engineer partners to… Keep up to date on products, technology, and codes and standards development Interact with Cummins experts and gain access to ongoing technical support Participate at your convenience, live or on-demand Earn PDH Technical tips:
Slide 3: Meet your panelists
Meet your panelists Cummins presenter: Rich Scroggins Technical Advisor, Global Application Engineering Cummins facilitator: Tom Bakritzes, Global Sales Training Manager Your local Cummins contacts: IL: John Kilinskis, Cummins Sales and Service, Central region TX: Scott Thomas, Cummins Sales and
Slide 4: Learning Objectives
Learning Objectives Participants will be able to: Describe NFPA requirements for arc flash incident energy calculation, labeling and PPE so that their designs appropriately address arc flash hazards. Define generator control arc flash mitigation capability so that their designs will minimize arc
Slide 5: The Challenge
The Challenge Arc Flash Incident Energy is directly proportional to arcing time – Minimize Arc Flash Hazard by instantaneously interrupting fault current Selective coordination isolates faults so that outages are limited to faulted circuits or equipment – Coordination is simplified by delayed in
Slide 6: What is Arc Flash?
What is Arc Flash? NFPA 70E Definitions Arc Flash Hazard – “A dangerous condition associated with the release of energy caused by an electric arc” Arc Flash Boundary. “a distance from … which a person could receive a second degree burn” – Incident energy = 1.2 cal/cm2 Arc Rating – The value at
Slide 7: NFPA 70E Requirements
NFPA 70E Requirements NFPA 70E requires an energized work permit when a “likelihood of injury from an exposure to an arc flash hazard exists” 130.2(A)(1)(2) The work permit shall include the results of an Arc Flash Risk Assessment The Arc Flash Risk Assessment shall determine 130.5(1) – Approp
Slide 8: Arc Flash Incident Energy Calculations
Arc Flash Incident Energy Calculations NFPA 70E refers to IEEE 1584 calculation method for three phase systems from 208 V to 15 kV. Arcing current is calculated as a function of bolted fault current Incident energy is not necessarily maximum at maximum arcing current – Lower arcing current may
Slide 9: Arc Flash with Decaying Current
Arc Flash with Decaying Current Some analysis programs account for decaying generator current in arc flash incident energy calculations *Reference – SKM Power Tools PowerHour Experts you trust. Excellence you count on.
Slide 10: NFPA 70 240.87 Arc Energy Reduction
NFPA 70 240.87 Arc Energy Reduction “Where the highest continuous current trip setting is 1200A or higher … one of the following or approved equivalent means (to reduce clearing time) shall be provided… … Energy-reducing maintenance switching … an energy reducing maintenance switch allows a worker t
Slide 11: Maintenance Mode on a generator set
Maintenance Mode on a generator set When maintenance mode is enabled genset will shut down instantaneously in the event of a short circuit, bypassing all time delays −Generator shuts down within 50 msec −Can also be configured to shunt trip a downstream breaker Running the genset in maintenance m
Slide 12: Modeling Arc Flash Incident Energy
Modeling Arc Flash Incident Energy Cummins PowerCommand AmpSentry is included in SKM as an overload protection device PowerHour Experts you trust. Excellence you count on.
Slide 13: Arc Flash Energy Reduction
Arc Flash Energy Reduction Reduce generator For maintenance mode set contribution based on Max Arcing Duration to 50 decrement curve msec + Td’ Set to 300% of rated – 50 msec for sensing current after Td’ Maintenance Mode results – Td’ for voltage decay in a substantial reduction Similar to
Slide 14: Selective coordination
Selective coordination Without Selective Coordination With Selective Coordination OPENS NOT AFFECTED OPENS UNNECESSARY NOT POWER LOSS Fault AFFECTED Fault NEC Article 100 Definition Coordination (Selective). Localization of an overcurrent condition to restrict outages to the circuit or equipment a
Slide 15: System Design Tradeoffs
System Design Tradeoffs Coordinated systems present challenges and tradeoffs – Fault Isolation – System Reliability – Equipment Protection – Safety Downstream equipment is exposed to fault current for a relatively long period of time – Is the equipment rated for this? NEC 110-10 violation – Incr
Slide 16: NEC 110-10 Overcurrent protection
NEC 110-10 Overcurrent protection : “The overcurrent protective devices, the total impedence, the component short circuit ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective device used to clear a fault to do so witho
Slide 17: Cable Protection
Cable Protection NEC 110-10 requires that cables are sized for short circuit current Delayed interruption requires larger cable Larger cable results in lower resistance Lower resistance results in more arc flash energy downstream PowerHour Experts you trust. Excellence you count on.
Slide 18: Coordination Studies
Coordination Studies Coordination Studies are based on available fault current in the event of a 3 phase bolted fault – A 3 phase bolted fault rarely occurs in practice – Delayed interruption results in extremely high arc flash energy Single phase arcing ground faults are much more common – Lowe
Slide 19: Definition of Selective Coordination for Health Care Facilities
Definition of Selective Coordination for Health Care Facilities NFPA 99 and NEC 517 do not require coordination in the instantaneous region “Overcurrent protective devices serving the essential electrical system shall selectively coordinate for the period of time that a fault’s duration extends beyo
Slide 20: Selective Coordination in Health Care Facilities
Selective Coordination in Health Care Facilities NFPA 99 Health Care Facilities code requires coordination for the fault’s duration beyond 0.1 sec – Coordination not required in the instantaneous region of the breaker trip curve NFPA 70 definition refers to “full range of overcurrent protective
Slide 21: Selective Coordination in other facilities
Selective Coordination in other facilities NFPA 110 Standard for Emergency and Standby Power Systems – 6.5.1: “The overcurrent devices in the EPSS shall be coordinated to optimize selective tripping of the circuit overcurrent protective devices…” – A.6.5.1 “It is important that the various overcur
Slide 22: Conclusions and Recommendations
Conclusions and Recommendations Arc flash incident energy is directly proportional to arc clearing time Maintenance switching is recognized by the NEC as a means of arc energy reduction Delayed interruption of fault current exposes cable, equipment and operators to high levels of energy Sizi
Slide 23: Q&A
Q&A Type your questions, comments, feedback in the WebEx Q&A box. We will get to as many questions as we can We will publish consolidated FAQ along with presentation and webinar recording on powersuite.cummins.com Your local Cummins contacts: AZ, ID, NM, NV: Carl Knapp (carl.knapp@cummins.com)
Slide 24: Closing
Closing Watch out for a follow-up email including – A Link to webinar recording and presentation – A PDH Certificate Visit powersuite.cummins.com for – PowerHour webinar recording, presentation and FAQ archive – Other Cummins Continuing Education programs – Sizing and spec development tool Ple