National Electric Coil (NEC)

Salient Pole Rotors


Hydrogenerators and other salient pole machines consist of a rotating spider mounted on a shaft with field poles mounted on the spider rim. We have manufactured new field poles for more than a dozen units whose frequency was increased from 25 cycles to 60 cycles, as well as cases where pole laminations were damaged in some way. We have also repaired casting cracks in older rotors, and we have made modifications to rotor rims and pole key assemblies to allow more pole weight and resolve distortion and re-fit issues. Because of the long lead time required to fabricated replacement rotors, our ability to fully rehabilitate these rotors can benefit your project budget and schedule.

For many years, NEC has provided hydrogenerator refurbishment services to several U.S. Government agencies and large investor owned utilities. These projects have involved the complete rehabilitation and refurbishment of large hydrogenerators.  Work scopes typically have included the refurbishment and re-insulation of rotor field windings. Our Rotating Equipment Service Center is set up to rewind salient rotor poles and to repair, refurbish, and re-qualify salient pole rotors.

With our engineering capabilities and dedicated manufacturing production line, we can easily address your field pole refurbishment needs, or should your project scope require it, the manufacture of completely new pole pieces.

NEC has identified several critical issues related to the rehabilitation and refurbishment of field poles in older hydrogenerators.  These include:

  • Bowing of the rotor field poles
  • Looseness of the field poles on the rotor
  • Fatigue of field pole connectors and leads
  • Cracking of field pole damper bars

These conditions have been seen repeatedly and can ultimately affect your unit's performance if not addressed properly. For an owner, prior knowledge of these types of problems may save time and money when planning a refurbishment project. Including provisions to address these conditions in your project scope work, should they be an issue with your machine, can mean improved reliability over the operational life of the unit once the project is complete.

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