Motor slows down ? and speeds up ?

[brinkmann27]

A while back we built a motor control panel for a customer, which controlled six 230/3/60 VAC motors. This system ran fine for many months. Customer had the system shutdown for a couple of months. Upon restart of the system, one motor (1/2 HP Fan motor) starts up, slows down and then speeds up a few times. Then the motor starter ( ABB DLA module)shuts the unit down. Customer claims all 3 phases are present at the motor, the contactor stays in (not cycling in and out) and the voltage is correct. Any ideas? Thanks in advance for all the help.

 

[testtech]

Your post did not indicate that this occurs in one or multiple fans. I assume that only one fan has these symptoms.

Unless this fan is in a critical operation, trouble shooting efforts will probably be limited since with such a small fan, replacement of components may be cheaper than extensive testing. Thus--low cost/no costs tests first.

I would also check to see that no fans are rotating backward during start-up, and, if dampers are present, they are closed for start-up. Make sure that static pressure characteristics cannot cause the motor to overload.

Observe the contactors during startup to ensure that chatter is not occuring. Check that all connections, particularly overload connections are tight so that there is no chance that the motor is single phasing. A visual inspection of the motor peckerhead terminations should be made.

Next, conduct vibration or ultrasonic testing on the fan bearings and motor to determine whether a bearing or other mechanical condition were causing this condition.

If desired, a disturbance analyzer can be used to confirm voltage condition seen by the motor during start-up. This will confirm proper contactor operation. Simultaneous current monitoring can indicate whether the motor loading during start-up is consistent with the motor rating and design.

If the fans and motors pass these preliminary tests, I would suspect an electrical fault in the motor.

Both rotor or stator faults could produce behavior of the sort described here. Since this is a small motor, the simplest approach at this point to trouble shooting may be to simply replace the motor, rather than pay for additional testing to deterime the condition of the motor rotor and stator.

 

[imok2]

Sounds like one set of motor windings are leaking and /or ready to fail

 

[jbartos]

Suggestion: The ABB DLA module tech support might be contacted.

 

[skiier]

check the bearings in your motor and see that you have good rotation. Tigten all your electrical connections.
Oh yes, what was the last thing that was done on this equipment? Sometimes troubleshooting is more detective work than anything else.
Connect the fan to a seperate supply and verify that it is ok. If fan ok then drive is suspect.
Isolate the problem. Good luck.