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Failed motor

Merry Christmas

kwired

Electron manager
Location
NE Nebraska
Occupation
EC
Little while back got a call for a crop drying fan not working. Though I fixed up some other shoddy things in the process, none of those were the cause of motor failure. An internal cooling fan on the motor shaft happened to decide to come off the shaft and ended up crashing into and damaging motor windings.

Not the first time I seen foreign material damage windings before but can't recall ever seeing such a fan come off the shaft without some external reason. I think welds simply gave up. I spread it open further than it was when I found it to get it past the bearing 1731514312570.jpeg

Replacement motor was about $1200, a definite purpose type motor for the application with a "air over" rating of 5 to 7 HP. Which is common thing to have that sort of rating on this type of equipment.

Not that many years ago same motor was only maybe about $400. :(

You can see near bottom right some arcing damage where it contacted motor windings. Couple other burns as well but near bottom is most obvious.
 

AJElectric

Member
Location
Iowa
Occupation
Electrical Contractor, instrumentation and controls integration
Never seen that before. Have seen the the actual fan blade come apart though - makes you think twice about where to stand when you're starting one up, especially newer dryers with thinner metal housing.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I had that happen on a 500HP Toshiba motor on an aeration blower when they started it across the line. I had built them a soft starter and they insisted on a bypass contactor rated to start it ATL in case the soft starter died. So we did the startup with the soft starter, everything went great. Switched to starting it ATL, the lights dimmed and the fan on the back of the motor came to pieces. Damned near peed my pants!

After that wherever someone asked for an ATL rated bypass for a large soft starter or VFD, I always ask them if they have enough power to do that anyway, and if they understand the mechanical risks…
 
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