Multiple motors on same feeder issue

[powersoff]

I had (13) 20hp,480volt 3phase motors running at the same time . The 480volt feed terminates at a tap block which then feeds fuses for each motor, contactor and ol's.
15 fuses feeding 5 motors blew.
That left me with 8 motors running.
Only 1 of the 5 motors was identified with a problem no continuity phase to phase.
The other 4 motors fuses were replaced and have been running ok.
The fuses that blew were mounted adjacent to each other on a din rail.
If 1 motor has a open winding could this have caused all 15 fuses to open?
The fuses are 45amp LPJ.
Thanks

 

[itsmoked]

Fuses for motors... Yuck.

If one leg has a different voltage than the others, the voltage imbalance can cause large current imbalances that could result in what happened.

A failed motor winding could precipitate this. It could also be a loose connection causing a brief single phasing of the whole bus that could blow lots of fuses and damage motors.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

The motor with an open winding may have had short circuited windings that then burned open. Probably did because open circuits rarely cause fuses to fail. Depending on the topology of your distribution system, the shorted motor may have dropped the bus voltage enough that the back EMF of the motors connected to the adjacent fuses caused enough regeneration to blow all the fuses.
Probably, but given the variety of fuse types available and not knowing your system topology it's not possible to say for sure.
Again depending on the system layout, don't be surprised if you start having random fuse failures on other motors. If you do, replace all three fuses in a group, not just the failed fuse(s). Even though all three fuses may not blow on a motor fault, the fuses that seem to have survived are often damaged by the surge that blew the other fuse(s) and may no longer be able to withstand normal duty.

Bill
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"Why not the best?"
Jimmy Carter

 

[jraef]

Bill, that is one of the biggest problems out there with fuse protection. People get "penny wise - pond foolish" after a fault, especially a costly one, and inadvertently end up creating the next failure point.

Then they get frustrated and start putting in bigger fuses...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[itsmoked]

quod erat demonstrandum - Q.E.D.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Hi jraej. I'd love to have a coffee (or whatever) with you and itsmoked and several other regulars here. We could swap stories for hours about the creative ways our clients have "Let the magic smoke out". LOL

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Hey Bill, at least it is your clients that let the magic smoke out. I seem to have gotten the knack for it myself.

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If we learn from our mistakes I'm getting a great education!

 

[waross]

Hi Scotty. Well I may have "Blown smoke" a few times myself as well. You are certainly welcome to join the virtual coffee club.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

"Now did I ever tell you about the time that I..."


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If we learn from our mistakes I'm getting a great education!

 

[powersoff]

Where no counsel is, the people fall: but in the multitude of counselors there is safety.


thanks