Overhaul & Testing of a 900KW AC Motor

At Fletcher Moorland all motor repairs are performed to the highest standards that have been audited and certified by SKF to ensure you have a reliable repair that operates efficiently. Large AC motors especially, represent a considerable investment by the customer and downtime on them is often extremely costly too. Making sure a repair is reliable is therefore of the utmost importance.

Large AC motors such as the one above present special challenges that only an experienced company with the appropriate facilities like Fletcher Moorland can successfully undertake. This is especially true when the customer has special requirements too. The customer requested that this two pole AC motor was tested for not at 3000 RPM, but at 3600 RPM on a 60 Hz supply.

The motor was fully overhauled in our workshops. The winding condition and integrity was checked using a Baker Surge Tester, even the winding inductance and capacitance to ground was measured as modern on-line PdM tools measure these readings. All these tests ensure there are no windings faults that can cause premature failures or increased energy losses.

The bearings, journals and housings were checked against the industry recommended tolerances. New SKF bearings were fitted by engineers trained by SKF in the correct practices for fitting bearings and the correct equipment to be used. This includes using a temperature controlled and degaussing bearing heater to prevent heat damage and leave residual magnetism in the bearing that can attract metal particles (There is no point in compromising the bearing before it has seen any service life). This all ensures that the bearings will be give reliable. On this motor an insulated bearing was also fitted to eliminate the possibility of electrical discharge damage occurring within the bearings due to circulating rotor currents. This is something that can drastically reduce the lifetime of bearings on large machines.

The rotor was balanced to G1 Standard, a much higher standard than most rewind companies will perform. After balancing it was re-assembled and tested by running it at 3600 RPM on a 60Hz supply using our large AC inverter as required by the customer.

The motor was run until the bearing temperatures, observed using an infra red camera, reached their plateau temperature. Vibration and bearing analysis was then carried out using our SKF conformance checker. This measures the vibration and separates the readings into frequency bands and compares them against a tight tolerance to ensure the vibration amplitude, displacement and velocity does not exceed recommended levels. This is shown in a table with bands measuring sub synchronous, rotational, 2 x rotational and bearing defect frequencies. This large AC motor after overhaul achieved broadband vibration values below 0.63mm/s.

Finally a comprehensive report was prepared for our customer, showing in detail every photograph taken, every bearing tolerances and dimensional measurements, and every test performed on this motor. This is something that takes us beyond anything our competitors do.

At Fletcher Moorland we take pride in “reliability engineering”, isolating the root cause of the failure and repairing your machines to the highest possible standards with the highest standard of reporting in the industry.

Take a look at the repair reporting we provide for a motor repair and see how this compares to your motor repair company.