300 hp DC motor knocking noise

[mturcott]

I have a 300 hp DC motor with a ABB DCS800 drive. While running the motor makes a knocking sound. When power is removed from the motor the noise goes completely away as it winds down, so it doesn't seem like the bearings. The noise is there when going up in speed and when going down it stops and then starts making the noise again when it meets desired speed. Am new to DC motors so any help would be appreciated.

 

[panter]

Look at the coupling and shaft connection. A loose joint can be a problem .

 

[itsmoked]

How about a loose stator?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Thrust bearing?


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[dArsonval]

The OP's third sentence, "...When power is removed from the motor the noise goes completely away...".

This statement declares fairly accurately the issue is electrical and not mechanical as other's are suggesting.

Direct Current motors in most instances are horizontal machines. They do not have thrust bearings. Vertical machines have thrust bearings.

Direct Current motors have a different nomenclature than Alternating Current motors.
D.C. motors have Field Frames. A. C. motors have stators.

Again, if the noise goes completely away with no power feeding the motor, a loose coupling/shaft fit would still be making noise.
According to the OP the noise disappears completely upon removal of power.

It's a control electrical issue. What that may be is going to take some careful study.

John

 

[dArsonval]

One more theory:
There is an OUTSIDE chance some portion of the machine is twisted per se.
During energized operation some part of the apparatus is "pulled" or "twisted" just enough to create a noise.
To pursue this theory the motor must be dismantled to fully inspect.

John

 

[waross]

What does the motor drive?

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

 

[btrueblood]

What is the frequency of the knocking sound, does it occur at the shaft rotation frequency (rpm/60 = Hz) or at some multiple of same? You can get smart phone apps that do a pretty good job of FFT spectra for noise, we diagnosed a vibration problem using one.

What is used to vary the speed, a potentiometer or a digital input? Have you scoped the input to verify that the signal going to the motor control is clean? Does the amplitude of the noise increase with rpm?

 

[ScottyUK]

Bearing not retained properly in the endshield, poor magnetic centering and/or axial thrust from the driven load causing the shaft to move axially?

 

[Tmoose]

OP ain't been back since OP on April 1.

April 1 . hmmm .....................