Induction Motor Failure Modes

[Technician]

Same old story about not wanting to part with cash

but I thought that a CNC machine would benefit from

a variable speed drive,  cutting speeds and all that.

 

[Sidewinder]

It does, they say they can live without it!

 

[revjames]

I remember a fault like this when I worked in a quarry. There was a bucket elevator which took washed gravel from the bottom of a crusher up to the top of the bins to be screened. The operator reported that after switching it off (DOL starter) the motor would continue running (quite quickly ) for a while. I went through everythiung, mad a few phone calls - one spark came up with a long winded plausible sounding but BS theory - which I can't recall.

I then remembered seeing the operator hosing down the elevator buckets (they built of a lot of mud inside after a while). I soon realised he hadnt finished cleaning them out so when the heavier muddy buckets were at the top and the motor stopped, they would drag the belt round until equilibrium was found!

 

[ProDave]

Cue the Barrel of Bricks

 

[Andy™]

Cue the Barrel of Bricks

well, you asked...

https://www.youtube.com/embed/Vt230Pd1oSo?feature=oembed

 

[OnOff]

Thinking back we maybe had something like this years ago on Tirak electric winches lifting man riding cradles. The winches, DOL, used in pairs, tended to be working near their load limit. Seem to remember it was to do with back EMF and the brake coil. The Lenze brakes themselves were all properly gapped etc. Same thing would happen even with a new brake! We videoed one system with the insurance man once.........you could be descending in the cradle with your finger on the down button and get someone to literally pull the mains plug - the cradle would carry on descending even though your finger was off the button. Banging the em.stop button didn't work either! The suppliers in Sheffield came up with a wiring mod but it was all kept pretty quiet. 

 

[Technician]

ProDave, on 22 May 2013 - 7:53 PM, said:
Cue the Barrel of Bricks
well, you asked...

Hoffnung did something exactly like this in

one of his sessions at the Oxford Union.

I fall out of my chair every time I hear it.