In today’s market, it is not always necessary to replace the entire Eddy Current Variable Speed drive system. Budget restraints and construction costs on large projects can hinder a complete remodel of an operation. This has been the case for large-horsepower applications that require medium-voltage (2,300 or 4,160 volt) motors. Variable Frequency Drives (VFD) in these applications are large, expensive and often require space that must be added on to existing buildings and be equipped with air conditioning systems that consume more power.
A recent refurbishment, done by Drive Source International/Dynamatic was a project of four pump motors housed in a pumping station for a New England Wastewater Service Plant. They were originally supplied by Electric Machinery in 1974. Replacing these units (and the pumps they serve) would have been a very expensive proposition, costing the municipality millions to replace them. Since all four units were still operational, it was decided to refurbish the pumps, motors and eddy current drives, replacing all bearings, carbon brushes, slip rings, and restoring worn machined surfaces to “as new” specifications.
Two of the units, are rated 1250 hp at 360 rpm and two at 800 hp 450 rpm, all equipped with brushless synchronous motors. Originally these units were chosen for their superior efficiency and power factor performance. The 1250 hp units were also equipped with eddy current drives for variable speed operation, but the 800 hp were constant speed. It was decided to retrofit the 800 hp motors with new SPMV-8240 eddy current drives to give all the units variable speed capability and increase flexibility of operation at the pumping station.
The scope of this refurbishment included:
- Perform incoming test run with vibration analysis per Dynamatic Specifications
- Disassemble complete motor per Dynamatic Procedures
- Micrometer check all bearing, housing and shaft clearances
- Check and document rotor and shaft run outs
- Mega-ohm meter prior to cleaning components
- Polarization index prior to cleaning components
- Surge test motor stator prior to cleaning components
- Inspect all motor stator blocking, welds, top sticks, connections, leads and overall integrity of the coils and stator frame
- Visually inspect the condition of all the motor components
- Core loss test motor stator
- Core loss test motor rotor
- Steam clean and bake dry all parts
- Test the insulation resistance of the motor brush holder assembly per Dynamatic Manufacturing Standards
- Micrometer inspection of slip ring TIR per Dynamatic Manufacturing Standards
- Meg-ohm meter after cleaning components
- Polarization index after cleaning components
- Surge test motor stator after cleaning components
- Re-torque all amortisseur-winding connections if bolted and not welded
- Precision balance motor rotor to Dynamatic Manufacturing Testing Standards
The fact that Eddy Current variable speed drive units can be in operation with minimal maintenance for decades, their controllers may become obsolete when it comes time to replace the aging system. The ability to retrofit the drive systems with new upgraded controls for increased monitoring capabilities is key. Drive Source International/Dynamatic supplied the refurbished pumping station for the Boston Metro Wastewater Service Plant our high-power EC-2000 controller. The programmable EC-2000, is carefully designed to be a compatible replacement, regardless of coil voltage or speed feedback format, for any known manufacturer of Eddy Current Drive, creating the total system.
This “refurbish instead of replace” strategy has been used with other Drive Source International/Dynamatic clients: St. Louis MSD chose a similar approach with a 1650 hp Ideal Electric synchronous motor and eddy current drive for their Bissel Point Treatment Plant. Metropolitan Water Reclamation District of Greater Chicago used this approach to restore reliable operation to a 1976 vintage 2250 hp 600 rpm synchronous motor and eddy current drive at another water reclamation plant.
The benefits of eddy current variable speed drives have long been recognized to include, lower energy cost, lower ownership cost and lower capital cost, but simplicity to maintain and repair, must be added to the list of benefits, extending the overall lifetime of the equipment. Before doing a complete teardown and replacement, an owner or engineer would do well to investigate if aftermarket re-manufacturing of an eddy current variable speed drive system might be a better an option to extend the life of the system.
Watch a short video of the refurbishment of one of the 1250 hp at 360 rpm units below: