CSE Pure Power - Summer 2008 - (Page 37)

37 ❮❮ © 2008 Caterpillar All Rights Reserved CAT, CATERPILLAR, their respective logos, “Caterpillar Yellow” and the POWER EDGE trade dress, as well as corporate and product identity used herein, are trademarks of Caterpillar and may not be used without permission. In a worst-case scenario, brand-new switchgear sections will have to be built from scratch, which requires several months of lead time. Meanwhile, manufacturing processes and budgets need to be reconﬁgured to account for an unexpected capital outlay, and the expectations of customers suddenly need to be managed. ACTIVE FAULT MITIGATION If you remove the source of heat from an arc fault as fast as possible to limit the pressure increase, potential damage to the switchgear and danger to nearby personnel is contained. That is the premise behind an active fault mitigation system, which is typically a bolt-on piece of equipment that is installed within the switchgear at the time of manufacture. (For more detailed information on active fault mitigation systems, see the IEEE article “Arc Terminator an Alternative to Arc-Prooﬁng,” authored by Ruben Garzon, paper No. PCIC-2001-19). Such systems use a high-speed electromechanical switch to control and direct the current ﬂow of the arc, as opposed to allowing the arc to continue in open air. The switch is closed by a signal from an electronic control module, which receives virtually simultaneous signals from two types of sensors: Current sensor, which detects discontinuity in the current waveform and the exceeding of a threshold current level Optical sensor, which visually detects the arc fault. The switch could be closed via the optical sensor signal alone, but the current sensor helps prevent a false trigger due to activation of the optical sensor by an irrelevant light source. When the switch closes, it provides a lowimpedance parallel path to effectively transfer the fault current from the arc to the switchgear’s three-phase main bus assembly. The main bus carries the fault current while it is being sensed and cleared by the switchgear’s current transformers, protective relaying and main breaker. Creating an alternate route for the arc fault by converting heat and pressure in this manner does result in mechanical stress within the capabilities of the switchgear on the main bus assembly, but that’s more desirable than switchgear replacement costs, or worse, accident litigation. In addition to reducing equipment damage, active fault mitigation systems also allow arc-resistant switchgear performance in rooms with low ceiling heights, since top-venting mechanisms are not required. Traditional passive systems must be vented to allow escape of ionized gases away from personnel in the immediate area. If inadequate ceiling height is avail- 10kW 4000kW One company is equal to both. • And everything in between, for that matter. With generator sets large and small, Caterpillar and your local Cat® Dealer can help you solve any challenge, whether it be powering large shopping complexes or supporting the small businesses right next door. And with service you can rely upon, Caterpillar is there for you every step of the way, backed by a powerful, worldwide dealer network. Need power in any shape or form? Caterpillar is equal to the challenge. To find out why, visit http://go.cateps.com/14b An active fault mitigation system uses a highspeed electromechanical switch to control and direct the current ﬂow of an arc. For more info, enter #415 on the Reader Service Card http://go.cateps.com/14b http://go.cateps.com/14b

Table of Contents Feed for the Digital Edition of CSE Pure Power - Summer 2008

CSE Pure Power - Summer 2008 Contents In the News Industry Roundup Risk Assessments for COPS Grounding Requires More Power Systems to Protect Healthcare Important Changes Coming in NFPA 70E A Look at Arc-Resistant Switchgear Agencies and Associations New Products Ad Index

CSE Pure Power - Summer 2008

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