It is currently Mon Sep 27, 2021 3:32 pm



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Correct Arc Flash label
PostPosted: Thu Dec 15, 2016 9:51 am 

Joined: Fri Nov 21, 2014 10:14 am
Posts: 23
Location: Edmonton, Alberta, Canada
If I have 2 Variable Frequency Drives fed from 2 different sources (protected by 2 different circuit breakers) and installed inside the same cabinet. what is the arc flash label that I should generate for this cabinet if the arc flash calculations for each VFD are different?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Correct Arc Flash label
PostPosted: Thu Dec 15, 2016 11:28 am 
Arc Level

Joined: Mon Jan 18, 2010 11:35 am
Posts: 544
Location: Wisconsin
jorgepaz wrote:
If I have 2 Variable Frequency Drives fed from 2 different sources (protected by 2 different circuit breakers) and installed inside the same cabinet. what is the arc flash label that I should generate for this cabinet if the arc flash calculations for each VFD are different?


I prefer to use a single label that shows the worst case hazard which are usually the highest voltage present and the largest Arc Flash Incident Energy.
The actual specifics for each calculation are contained in the report, so they are available for use with energized work permits.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Correct Arc Flash label
PostPosted: Thu Dec 15, 2016 2:38 pm 

Joined: Fri Nov 21, 2014 10:14 am
Posts: 23
Location: Edmonton, Alberta, Canada
thx a lot.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Correct Arc Flash label
PostPosted: Fri Dec 16, 2016 5:05 am 
Sparks Level
User avatar

Joined: Fri Jul 08, 2016 10:01 am
Posts: 227
Location: Indiana
Without seeing a pic of what you're describing I can't say for sure but for "normal" single standalone drives I don't label them. I don't consider them equipment that would be opened up while energized to maintain.

Since you have 2 drives though that situation may be different. I agree with the worst case suggestion if you indeed would likely need to access exposed live parts.

_________________
SKM jockey for hire


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Correct Arc Flash label
PostPosted: Fri Dec 16, 2016 10:50 am 
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
Label what they hook into since that's the largest incident energy you will see.

Within the drive you are limited to the drive's internal DC link storage which doesn't amount to enough to matter.

Externally/downstream of the drive you are severely limited by the drive's maximum output current which is normally in the specs. or often printed on the label. Another approach is to realize that the thyristors in the drive are rated according to their RMS rating so the maximum current output is sqrt(3) times that rating and this assumes that the switching device faults for some reason and goes into 100% conduction for a short period of time (2 seconds).

This is still vastly less current than you are likely to ever see on the input side and with regenerative drives, assumes that somehow you have a double fault across both thyristor bridges (very unlikely) or that the front end is a free wheeling diode bridge and actually allows this kind of thing to hapen...I don't see how but at least it gives you an ultra conservative worst case possible output even considering arbitrary hardware failures occur.


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 

All times are UTC - 7 hours


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
cron
© 2019 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883