A utility customer needed an emergency replacement motor for a high-inertia ID fan. PMW pulled a Siemens Allis 4500 HP, 8-pole, 6600V WPII squirrel cage induction motor from our large inventory, redesigned the stator winding for optimized temperature rise at 5000 HP with a 1.15 service factor, rewound it with new Class F insulated VPI windings, and completed full diagnostics and assembly. This was the second of two machines provided from PMW inventory on an emergency basis for the same customer.
From Inventory to Redesigned 5000 HP Machine
The original motor was nameplate rated at 4500 HP and 893 RPM. Rather than simply refurbishing it to original specifications, PMW's engineering team redesigned the stator winding to optimize operational temperature rise, bringing the machine up to a 5000 HP rating with a 1.15 service factor. This kind of redesign work requires careful thermal analysis of the winding configuration to ensure the motor can handle the increased output without exceeding safe temperature limits, particularly important in a high-inertia ID fan application where starting duty and continuous load both stress the insulation system.
Stator Rewind and VPI
The stator was completely stripped and rewound with new Class F insulated windings. After winding, the stator went through our vacuum pressure impregnation (VPI) process, which forces resin deep into the winding structure to eliminate voids and lock the coils in place. VPI provides superior resistance to moisture, contamination, and the mechanical forces that act on the windings during starts and normal operation.
Rotor Inspection and Bearing Work
The rotor was removed and set up on a workbench for detailed examination of the shaft, spider assembly, and rotor bars. On a high-inertia fan drive, the rotor sees significant mechanical stress during every start, so thorough inspection is essential.
Our technicians inspected and serviced the sleeve bearing assemblies, confirming proper fit and oil clearance in each pedestal.
Air Gap Measurement and Assembly Diagnostics
With the bearings set and the rotor installed in the freshly wound stator, we performed air gap measurements at multiple points around the bore. Uniform air gap ensures balanced magnetic pull and smooth operation. The air gap measurements came back satisfactory.
Every accessory on the motor, including temperature detectors, space heaters, and junction box connections, was inspected and functionally tested. All accessory checks returned satisfactory results. We also completed a full set of horizontal motor dimensions to confirm that all fits and tolerances were within specification. The assembly diagnostics covered the complete mechanical and electrical build, and every checkpoint was verified satisfactory before the motor moved to final paint and closeout.
Final Assembly and Delivery
Once all inspections and tests were complete, the motor was fully reassembled, painted, and prepared for delivery to the customer.
This project demonstrates what PMW can do when a customer needs a motor fast. By maintaining a deep inventory of large medium-voltage machines and combining that with in-house redesign, rewinding, and VPI capability, we can deliver a motor that is not just refurbished but engineered specifically for the application.
Need an Emergency Motor Solution?
If you need a large motor on short notice, or if you have a machine that needs redesign and rewinding, contact PMW at (918) 752-0309 or visit our contact page. Browse our repair services or check our AC squirrel cage motor inventory for available units.
