Powder coated generator field coils and related method

#This invention relates to the manufacture of generator electromagnetic rotors, primarily for use in power generating equipment.

#In conventional processes for manufacturing generator electromagnetic rotors, the current-carrying copper coils (called “field coils”) are laboriously hand insulated. Each coil must be insulated from other coils, and the entire coil package must be insulated from the steel of the rotor. Significant cost savings and productivity improvements could be realized with a simpler and faster insulation system.

#It is now proposed to coat the copper field coils with a suitable powder resin. The coating can be applied by electrostatic spraying or other suitable process. In one technique, the field coils remain stationary while electrostatic spray guns revolve around the coils. In an alternative technique, the coils are carried along a conveyor through a power spray booth. With either technique, the resin powder can be cured onto the field coils using resistance heating, induction heating, convection heating or infrared heating. Two coats of the resin powder are required to ensure complete coverage. In addition, and depending on the coil configuration, the ends of the copper bars may be masked to prevent powder coverage where not desired (for example, at the site of the electrical connections).

#FIG. 1 is a partial perspective view of a known field coil configuration; and

#FIG. 2 is a flow diagram of a field coil coating process in accordance with this invention.

#With reference to FIG. 1, a copper field coil 10 is shown that is of the helical wound type, with multiple layers or windings 12 formed from a single copper bar. The longitudinal sides 14, 16 of the windings are received within radial slots in the rotor body, while the ends 18, 20 of the windings project beyond the slots. In an alternative coil construction, each layer is comprised of a single winding or bar, the windings ultimately secured together in a stacked arrangement within the rotor slots. The present invention is equally applicable to either field coil construction.

#The invention here relates to the elimination of known wrap-type insulation in favor of a powder resin coating. In an exemplary embodiment, two coats of a suitable resin powder coating are applied to the field coil 10. Prior to coating, the coil ends where the electrical connectors are located, are masked off, one such connector shown at 22. The masking can be done with Teflon® sleeves or other suitable means.

#Three classes of powder resins are preferred as coating compositions for the field coils. They include epoxy powder resins, silicone powder, and silicone hybrid resin systems (silicone/epoxies and silicones/acrylics). Examples are provided in Table 1 below.