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| Variable Frequency Drives and Arc Flash Warning Labels https://brainfiller.com/arcflashforum/viewtopic.php?f=33&t=2968 |
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| Author: | Jim Phillips (brainfiller) [ Sun Sep 01, 2013 3:46 pm ] |
| Post subject: | Variable Frequency Drives and Arc Flash Warning Labels |
Continuing the series about what equipment should receive an arc flash warning label, here is another question that a member submitted: Do you believe arc flash warning labels should be on variable frequency drives?
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| Author: | Larry Stutts [ Tue Sep 03, 2013 6:47 am ] |
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I think the arc flash ratings are a bit more complex with a variable speed drive. You have the input bridge section that is AC, and the DC Bus section that is DC, then there is the output bridge section that is PWM AC. Depending on where the short occurs and the state of the inverter when the short occurs determines the magnitude of the arc flash incident. If you have a short on the output before the drive energizes, you would get an instantaneous overcurrent trip. |
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| Author: | jdsmith [ Fri Sep 06, 2013 6:29 pm ] |
| Post subject: | |
This gets into a hairy subject since the DC link of the drive has stored energy in addition to some DC voltage and short circuit availability based on the short time rating of the rectifier and the upstream AC source. The output stage of the drive is not of particular concern since the incident energy there is almost certainly less than the incident energy on the AC input ahead of the rectifier. Since the idea is to apply labels at locations where personnel could be exposed to arc flash hazards, most customers will want to take voltage or current measurements while the drive is energized and therefore ask for a label on their drives. Typically the DC link and the inverter output are neglected and the incident energy is calculated at the line side terminals of the drive assuming a panel-sized bus gap. |
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| Author: | Ricky [ Mon Sep 30, 2013 4:40 pm ] |
| Post subject: | |
I have a concern about a panel that is HRC 0 and has a arc flash boundary of 9 inches. If i operate the keypad of the VFD , the way I interpret the code, I would need my PPE on, including gloves to do this . Is this correct ? Has anyone had difficulty using the keypad on a VFD with their gloves on ? Under the definition of a Arc Flash Hazard, informational note #1 says "Under normal conditions, enclosed energized equipment that has been properly installed and maintained is not likely to pose an arc flash hazard. " (NFPA 70E). Does a vfd meet this requirment ? thanks, Ricky |
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| Author: | wbd [ Tue Oct 01, 2013 8:28 am ] |
| Post subject: | |
I don't think operating a keypad is interacting with the equipment in a manner that may cause an arc flash. Most likely that keypad is the HMI to the microprocessor which will output a low voltage signal to a relay to provide power to a contactor to turn on the motor. That is simplistic and I did not talk about the power electronics but I would and have never seen anyone operate a keypad with PPE |
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| Author: | Larry Stutts [ Thu Oct 03, 2013 5:27 am ] |
| Post subject: | |
I have operated a speed potentiometer on the front of a 40Hp inverter one time where it resulted in a catastrophic failure - a large amount of plasma shot out the front of the drive. It was a case where an OEM had just reassembled the power bridge incorrectly (he put the flyback diodes in backwards and as soon as the output voltage exceeded 0.6V, they acted as a dead short across the output phases). I, of course, was standing to the side of the inverter when this happened. This was in the 1990's, so typically there was no PPE used. |
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| Author: | Ricky [ Wed Oct 09, 2013 3:57 pm ] |
| Post subject: | |
Sounds scarry Larry. The way I understand the code from nfpa 70e, your hand would be in the flash boundary zone and would require ppe. I figure when we need to do this , we could use a pen or stylus to tap the keypad. Most of our drives are on a network , so we can connect using a pc . |
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| Author: | Larry Stutts [ Thu Oct 10, 2013 5:34 am ] |
| Post subject: | |
Ricky wrote: Sounds scarry Larry. The way I understand the code from nfpa 70e, your hand would be in the flash boundary zone and would require ppe. I figure when we need to do this , we could use a pen or stylus to tap the keypad. Most of our drives are on a network , so we can connect using a pc . This happened 20 years ago. There was no keypad - it was actually a potentiometer on the front of the drive at that time. |
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| Author: | Flash [ Thu Oct 10, 2013 2:35 pm ] |
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If you mount your input fuses/disc sw outside the the main drive cabinet you will normally have a HRC #0. This is similar to the Hoffman Sequestor option. The fuse type can be a Class j fast acting fuse up to 400 amps and it must be a semi-conductor fuse over 400 amps and as high as 1200A. In affect, if I mount a fuse like Mersen A50QS800 on the outside of the drive cabinet, you are going to be Hrc#0 way over 50% of the time inside the drive cabinet. You need to use the Hoffmann door solenoid interlock and aux contacts on the remote switch. When I say remote, it is typically attached to the right side of the drive cabinet. I keep using HRC#0, I basically mean less than 1.2 ca;/sqcm. |
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| Author: | Larry Stutts [ Fri Oct 11, 2013 5:14 am ] |
| Post subject: | |
In this particular instance, the inverter was NEMA 1 mounted directly on the wall - the top cover was open to make the adjustments during the start up |
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