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 Post subject: CB Operation Doors Closed
PostPosted: Wed Apr 15, 2009 5:34 am 
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Location: Canton, OH
Need some advice.....

The situation in question is the operation of 5kV switchgear breakers with the doors closed. I performed an arc flash study several years ago (2005) based on IEEE 1584 standards and the incident energy level was calculated to be 60cal. The PPE level is >4 and the label states never work on or near while energized. The arc flash protection boundary was calculated to be 168ft!

The client would like to know how they can safely open and close these breakers. There is a master control panel located 40ft away which allows you to remotely open/close these breakers. The electricians believe they can not open or close these breakers via the master control panel because it is located within the flash protection boundary.

My opinion is the arc flash protection boundary is used and PPE must be worn when there are exposed live parts. With the doors closed you should not have to wear PPE when you are standing 40' away operating breakers remotely. But what about control switch operation of a 5kV CB while standing in front of the gear. NFPA 70E 2009 has indicated there are inherenet risks associated when working on equipment with the covers on and for this specific task the task tables require CAT 2.

When do you distinguish between IEEE 1584 results and the task tables? When you label equipment based on IEEE 1584 studies do you distinguish between covers on/off? Do you follow the label when there are exposed parts and use the NFPA tables when covers are on?

Lots of question I know..............Please Help!!


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PostPosted: Wed Apr 15, 2009 6:04 am 
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GPD_Steve wrote:
The situation in question is the operation of 5kV switchgear breakers with the doors closed. I performed an arc flash study several years ago (2005) based on IEEE 1584 standards and the incident energy level was calculated to be 60cal. The PPE level is >4 and the label states never work on or near while energized. The arc flash protection boundary was calculated to be 168ft!

The client would like to know how they can safely open and close these breakers. There is a master control panel located 40ft away which allows you to remotely open/close these breakers. The electricians believe they can not open or close these breakers via the master control panel because it is located within the flash protection boundary.


Calulate the Ei at the control panel and wear the correct PPE based on that result.

GPD_Steve wrote:
My opinion is the arc flash protection boundary is used and PPE must be worn when there are exposed live parts.


Unless the swgr is arc rated you need to wear the same PPE doors open or closed to operate that breaker based on your calulated Ei.

GPD_Steve wrote:
With the doors closed you should not have to wear PPE when you are standing 40' away operating breakers remotely. But what about control switch operation of a 5kV CB while standing in front of the gear. NFPA 70E 2009 has indicated there are inherenet risks associated when working on equipment with the covers on and for this specific task the task tables require CAT 2.


Forget about the tables, you have done the analysis and identified the hazard level, you are obligated to protect your employees from that hazard, cant go back to the tables now.


GPD_Steve wrote:

When do you distinguish between IEEE 1584 results and the task tables? When you label equipment based on IEEE 1584 studies do you distinguish between covers on/off? Do you follow the label when there are exposed parts and use the NFPA tables when covers are on?


Again, you cant mix the tables and analysis results. Also there is no calculation for the doors closed, dosent exist (yet).


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PostPosted: Wed Apr 15, 2009 12:44 pm 
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"Unless the swgr is arc rated you need to wear the same PPE doors open or closed to operate that breaker based on your calulated Ei."

Thanks for the reply Zog.
If I understand correctly then anyone within the arc flash boundary of 168ft must wear PPE when work is performed. You don't enforce PPE requirments within the boundary when no work is being performed do you?


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PostPosted: Wed Apr 15, 2009 12:59 pm 
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Location: Charlotte, NC
GPD Steve:

if you recall, what was the clearing time of the 60 cal, 168 ft. equipment?


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PostPosted: Wed Apr 15, 2009 1:20 pm 
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Location: Canton, OH
4.16kV, 38.3kA, 36" working distance, 1.325 sec 3 phase fault duration.

It is a water puming plant with several large (2000HP) synchronous pump motors and three 2500kW generators that can be operated for peak shaving. Lot's of fault current! We are looking for ways to mitigate the exposure.


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PostPosted: Wed Apr 15, 2009 2:25 pm 
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Now that IS a stiff one! 1.3 secs. @38 kA seems long as well. Is the time required for the large motor starting? If so, could you ramp them up slowly so you could crank down on the time curve? How bout an instantaneous trip for maintenance settings?


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PostPosted: Wed Apr 15, 2009 4:16 pm 
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GPD_Steve wrote:
"Unless the swgr is arc rated you need to wear the same PPE doors open or closed to operate that breaker based on your calulated Ei."

Thanks for the reply Zog.
If I understand correctly then anyone within the arc flash boundary of 168ft must wear PPE when work is performed. You don't enforce PPE requirments within the boundary when no work is being performed do you?


You got it right, only when someone is interacting with the equipment.


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PostPosted: Thu Apr 16, 2009 7:24 am 
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Alan,
The local utility owns the upstream protection. We have the settings and will propose a modified setting to the utility. Since they are both city utilities I imagine the power utility will be more willing to accomodate us.


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PostPosted: Tue May 26, 2009 11:31 am 
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[ You don't enforce PPE requirments within the boundary when no work is being performed do you?[/QUOTE]

according to what i read in the code you have to wear the ppe for this hazard whenever you cross the arc protection boundry wheither you are working on that equipment or near that equipment provided that others are working on that equipment
correct?


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PostPosted: Tue Jun 02, 2009 2:15 pm 
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How about using current limiting fuses. These will reduce the arc flash boundry, can be installed on the incoming feed and will majorily reduce the chances of a severe arc flash failure. We retro fitted all of our medium voltage fuses to reduce the dangers of a flashover and meltdown. We have had two tests of the system and in both cases the fuses shut down the blast with minimal damage to the switchgear. In neither case did it blow open any doors or covers. It has made me a believer in current limiting fuses all the way to the utility.


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PostPosted: Wed Jun 03, 2009 11:14 am 
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Current limiting fuses on the primary will not be in the current limiting range for a secondary (through) fault. The current-limiting characteristic therefore will not reduce arc hazard risk on the secondary. The CL fuse might have a lower clearing time than the non-CL fuse that it replaces, but not necessarily. You have to consider inrush when sizing the primary fuse, whether current limiting or not.


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PostPosted: Wed Jun 03, 2009 6:35 pm 
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My first thought is that some information or assumption is wrong. A 168ft AFB is ridiculous. There is no way you have this magnitude of energy. It would level the building. What time duration did you assume on the primary protection? You said greater than 4 cal, did you mean greater than 400? There is a relationship between IE and AFB. AFB uses the same formula just solves for an IE of 1.2 cals. So if you have 1.2 cals at 168ft, you'd have to have 500 cals at the switchgear. Thats not likely.

Switchgear is the intent of the new stipulation of full PPE even with doors closed when switching high energy devices. I usually limit it to that and don't go further down the distribution line.

The CLF probably won't have much of an effect on Isc, but they would have a big effect on clearing time. You need lower t. The other idea would be inline reactors to reduce Isc. You should post the specifics so we can see if we come up with the same results. Also, there are multiple ways to calculate AFB, which formula are you using.


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