Case Studies: Brushless Exciters

Case Study: Hydrogen-Cooled Exciter

Exciter unit incoming at NEC's Rotating Equipment Service Center. During operation, this vessel is pressurized with hydrogen.
Rewind of the AC exciter armature in progress.
Exciter unit incoming at NEC's Rotating Equipment Service Center. During operation, this vessel is pressurized with hydrogen.
Reassembled unit prior to transport to owner's site.

Project involved the total rewind and refurbishment of a hydrogen-cooled exciter, one of the largest of its type.

  • Unit nameplate: Siemens MarkII, 4500 kW, 525 Volts, 8575 Amperes, and 3600 rpm. This unit provides excitation for a generator rated at 970 MVA, 22 kV, and 3600 rpm.
  • The unit had been exhibiting an increasing demand for field current over a period of about a year.
  • During the scheduled outage, inspection of the unit showed the failure of phase its lead retention band and the unit was scheduled for immediate refurbishment and rewind,
  • Because the the failure of the retention banding there was considerable damage to phase leads and deformation of 34 of 36 phase lead connectors resulted.
  • Lack of support also lead to extensive damage to inboard and outboard armature coil connections
  • NEC redesigned phase lead connectors to add more stability. Profile was reshaped and cross section was increased.
  • Diode wheel fuses and capacitors were tested and replaced.
  • All parts of the exciter were thoroughly cleaned: two diode wheels, PMG, AC armature and its components.
  • NEC rewound the unit's AC Exciter armature and replaced and the glass banding.
  • After the start-up was completed and the unit running at full load, the exciter DC currents was measured
    at lower levels than the pre-outage level.
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