400 HP Failure Yearly 2

[jnorris04]

thread237-329180

Coming back to this thread referenced above. The motor has been running for 9 years now and has not failed since fixing the vibration problem.

 

[waross]

Thank you for the update.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[electricpete]

Yes, definitely thanks for the feedback. Another LPS for you.

It's an interesting case study. If you have any more details to add (photos of windings) those would make it even better, but that's up to you.

I have a 400 hp motor on a hammermill that has failed every year for the past seven years.

The motor is equipped with a telamecanique altistart 48 soft start and is 3 phase 480 volt. This hammermill is used to grind corn for a feed mill.

When the motors are taken to a motor shop, it always reveals that it appears to be an overload. After studying how the hammermill is operated, it is never overloaded nor exceeds its nominal nameplate current. The softstart, I believe, has been programmed correctly.

We have tried several different brands of motors and all have had the same result. The insulation is deterioted and goes to ground.

....Motor is cleaned atleast once a day to remove buildup. I did a thermal study on this motor and the temperature of the exterior of the motor never got above 105 degrees.

UPDATE: I did a vibration analysis on the machine, and the result was the base was flexing and that the anchor system was not Sufficient. After reanchoring and grouting the machine, also found that the rotor inside the machine was out of tolerance by an eight of an inch causing an imbalance. Replaced rotor, vibration has disappeared.

....Motor shop confirmed, after going through the motor, that the losses were contributed by vibration. I will not be certain that this fixes the problem until after a year of running the new motor because failure usually occurs 10-12 months from installation. I am pretty confident this fixes the problem because everything from the peckerhead back to the motor control panel and components inside motor control cabinet have been replaced. Vibration on the horizontal plane of the motor was .933 in/sec, which is double the permissible limit.
After repairs were made, vibration was .185 in/sec.

1/8" out of tolerance is indeed pretty bad for a motor rotor assuming it reflects the position of the rotor in a certain axial plane (rather than localized roughness). It might well explain the 0.933 ips all by itself. If it's 1 / 8" TIR then it could be 1/16" on each side. I'd say for this size motor the airgap on each side might not be too much more than 1/16". Did they see any rotor/stator rubs? Do they have any idea how the rotor got that way?

I'm having a hard time imagining the rotor was that way throughout a series of trips to the shop for winding failures and they never identified it until the end.

How did the vibration track during the course of these stator failures (always there, slow increase, sudden increase).

Do you recall if they ran the motor uncoupled near the end, and whether that 0.9 ips vibration was the same level uncoupled?


=====================================
(2B)+(2B)' ?

 

[Compositepro]

I believe the mentioned "rotor" was in the hammer-mill, not the motor.

 

[electricpete]

All I see with reference to the rotor is "machine" which in itself is ambiguous. I had assumed it meant motor rotor because it was implied that the vibration was causing the winding failures and he did say "Vibration on the horizontal plane of the motor was .933 in/sec". But you know what they say about assumptions... it's worth for op to clarify.

=====================================
(2B)+(2B)' ?