Field Pole Windings

NEC has expertise with both new and refurbished windings for salient pole rewinds.

With our engineering capabilities and dedicated manufacturing production line, we can easily address your field pole refurbishment needs, and should your project scope require it, NEC can manufacture completely new pole pieces. A general scope for field pole refurbishment is given below.

  • Remove field poles from rotor
  • Remove field coil from field pole
  • Remove all insulation and resin from coil and pole
  • Apply ground insulation to pole
  • Apply turn insulation to new or refurbished copper coil
  • Install newly insulated coil onto pole
  • Install refurbished pole onto rotor

Rotor Repairs &
Re-qualifications

Hydrogenerator rotors consist of a rotating spider mounted on a shaft with field poles mounted on the spider rim. Because of improvements in insulating materials, older hydrogenerator units can often be significantly uprated through the redesign of the stator winding. If a frequency change also is involved, the number of field poles may need to be changed. In either case, the rotor may require repairs or modifications to re-qualify it to meet the new rating.

NEC is experienced with cast and fabricated rotors, including those with segmented rims. 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.

Uprate Affects Rotor
Because of improvements in insulating materials, older hydrogenerator units can often be significantly uprated through the redesign of the stator winding. The mechanical impacts on the rotor of these changes must also be considered. Download a technical paper discussing these mechanical issues.
New Field Pole Manufacture
NEC has 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. In a recent 10-year period, NEC refurbished almost 2,000 field poles. For many, NEC manufactured new replacement copper windings for the poles.
Laminated Rotor Rims May Need a Shrink
Age can affect the concentricity of a laminated rotor rim causing the rotor poles to become loose at operating speeds. Our Technical Maintenance Memo, TMM 601, addresses the causes and repair solutions for the problem affecting older rotors. Download a copy.
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