arc flash study

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anbm

Senior Member
If arc flash study indicates that incident level at main gear (480Y/277V, 3PH) exceed level 4? What will we do to comply with code? Most of the time when you have poco xfmr larger than 2,000kVA (480V secondary), the arc flash incident level will likely over level 4.
 

jim dungar

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Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
What will we do to comply with code?
What are you trying to do? Walk past the equipment or maybe "interacting with the equipment in a manner that could cause an electric arc (NFPA70E)"?
 

anbm

Senior Member
No, I meant we can specify the main gear with main shut trip breaker and we can remotely turn it off when servicing the gear... but then, I am wondering how we turn on that breaker back on...
 

charlie b

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Location
Seattle, WA
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Electrical Engineer
Depending on the type of gear (i.e., switchboard construction versus switchgear construction) and the manufacturer, you may be able to get a main breaker with a "maintenance mode" feature. That will allow for a faster trip time, and therefore a lower arc flash energy, and can be manually selected whenever you need to "interact" with the board. This feature essentially disables any selective coordination you might have established, so that a short circuit in a 100 watt 120 volt light bulb might cause the main breaker to trip. But you must accept that risk, during the time that maintenance is being done, and you must manually return the main breaker to its normal trip mode after the maintenance is finished.

There are other features available that can reduce the arc flash hazard. There is an arc quenching cubicle, and there is a board designed to cause all arc energy to be forced upwards (i.e., blowing off the top of the board, but not harming a person standing in front of the board). In addition to remote operators, there are tools that provide an arc shield (kind of like an umbrella) that protects the worker (standing behind the shield) while operating the equipment. Check with the manufacturer, to see what they offer.
 

zog

Senior Member
Location
Charlotte, NC
Depending on the type of gear (i.e., switchboard construction versus switchgear construction) and the manufacturer, you may be able to get a main breaker with a "maintenance mode" feature. That will allow for a faster trip time, and therefore a lower arc flash energy, and can be manually selected whenever you need to "interact" with the board. This feature essentially disables any selective coordination you might have established, so that a short circuit in a 100 watt 120 volt light bulb might cause the main breaker to trip. But you must accept that risk, during the time that maintenance is being done, and you must manually return the main breaker to its normal trip mode after the maintenance is finished.


That is a great solution for the feeder breakers and switchgear but does not reduce the hazard at the main breaker.
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
This might reduce fault current but that often (at least in my calculations) results in longer OCPD clearing time and higher PPE requirements.

Yes, that is possible, agreed. :thumbsup: Would need to reduce the current AND increase time coordination to achieve desired result assuming you have adjustable relays.
 

OBI213

Member
why you cant turn the breaker back on. Just close the switchboard back up and close the breaker. You will not be exposed to the gear.
 

GearMan

Member
Location
WI
Not to sound like a GE commercial but below is a great product we have used. A bit spendy. Below is the GE ad.

It doesn't take much to unleash an arc flash- but the consequences can be devastating. A wrench slipping from a worker's hand can produce a disastrous explosion that can maim or kill employees, destroy equipment, and disrupt a facility for weeks.

The main line of defense against arc flashes is to prevent them, but when flashes do occur, most electrical systems are ill prepared to contain them. That's because the traditional techniques used to handle flashes are rudimentary. Traditional arc-resistant switchgear is designed not to eliminate the flash, but to muffle it, exhausting its energy through a chimney or plenum. It provides no protection for equipment. Even worse, its effectiveness can be severely compromised if a cabinet door is open or a panel is off- as it is likely to be during routine maintenance.

GE's innovative Arc Vault? takes a different approach. It doesn't exhaust the arc flash; it extinguishes it. Arc Vault? can stop an arcing fault in less than eight milliseconds, a fraction of the time that traditional systems need to stop a flash.

Arc Vault? sets the new standard for arc fault protection, but that's not the whole story. It also saves you money. By reducing downtime, decreasing switchgear damage, and the ability to be added as a retrofit, it enables you to maximize your return on your existing equipment.

Arc Vault? is another way GE uses technology to add value to your business.

Request Publications: Receive a set of Arc Vault publications.
 
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