Customer: 

Quarry Operator

Customer Job Reference: 

1491RPM, 930A, 400 Frame, B3 400V/690V

JJ Loughran Job Reference: 

Job No: 17735

Background: 

Customer was concerned about excess noise from the motor onsite. Motor was critical to Quarry operation. As a result JJ Loughran had a reduced time window to assess motor & carry out all necessary repairs.

The Solution: 

JJ Loughran had to first verify the noise issue with the motor, so we initially checked the motor and found no obvious issues.

We then connected the motor to our VSD Drive and ramped to 50HZ in 10Hz stages (we record vibration levels at each stage). We quickly concluded that there was excess noise and vibration.

We then proceeded to remove the motor fan and fan cowl and dismantle the motors front and back end caps. The motor had the following bearings.

Drive  End  = Fag  NU 224 E + FAG-6224 C3 ( front bearing housing had 2 bearings)

Non Drive = FAG-NU 224 E ( Had one bearing only, which was a roller bearing)

The non-drive bearing was not insulated even though the motor is supplied by a VSD drive. This is against industry standard for this size of motor.

After removing the motor end caps, we fully inspected the motor, we found liquefied grease in the bottom of the stator housing

We cleaned and checked the bearingswe had found the Inner race & rolling elements had started to become “frosted”. Which will eventually lead to, Vibrations + arcing = Fluting, Flutes form on outer race on the bearing . This will increase Noise, temperature & vibration dramatically.

Engineering manager briefed the customer of all our finding in a detailed report.

We then changed all three motor bearings on the motor including a non-drive end insulated back bearing.

We Checked with Siemens the motor tolerances for this motor in regards to the front end cap and the horizontal tolerances of the rotor.

We balanced the rotor to ensure it is in tolerance, using JJ loughran’s state of the art IRD soft balancing machine.

We Ensured Grease used by customer had a high enough melting point (dropping point). As our reports showed liquefied grease inside the motor. However this may be a result of the Non drive bearing not being insulated, and not as a result of the grease that has been used.

A Full varnish / Re- lacquering and stoving of motor windings was carried out.

Reassembly of all parts and a test run of the Siemens motor at different frequencies on our test bed. All results including vibration, rpm, torque, speed and amps were recorded. As a result of all works carried out there was no excess noise or vibration.

Full re-spray of generator to original Siemens paint specification.

Dispatched the Motor back to the customer on a 3 day turnaround.