Exciter Maintenance, Repairs & Overhauls

Brushless exciters are uniquely complex machines.
Maintenance? or Overhaul? NEC is a one-stop solution!

In the hands of the inexperienced, brushless exciters appear deceptively simple. The real expert will not fail to recognize their innate complexity. Indeed, the design of the brushless exciter – with its many rotating and high-voltage component parts – is often at the root of the most common failure modes. Age, contamination and stress are the triple enemies of reliable operation of rotating brushless exciters.

NEC's exciter rewind and maintenance programs assign the highest priorities to schedule and customer service. Our engineers and electromechanical technicians have extensive experience with all standard exciter failure modes and maintenance requirements. NEC manufactures replacement armature coils, leads and other electrical parts. Whether a complete refurbishment, including rewind, as shown in the picture above, or a maintenance overhaul and cleaning, NEC's goal is to get your machine back in operation expeditiously.

Expert Exciter Maintenance Services

National Electric Coil's Columbus Service Facility - The NEC service facility provides a unique combination of experience, shop capabilities and technical resources especially well-suited to the overhaul of single and double wheel brushless exciters. NEC has overhauled and rewound brushless exciters for over 20 years. Exciters can be received as a complete unit at the facility.

Additionally, NEC has the ability to dynamically balance exciters at rated speed and subject them to over-speed testing. This dynamic balancing is very important, considering the number of rectifier components present that can affect the unit's balance at running speed. Photo above shows the reinstallation of a large Siemens Westinghouse hydrogen-cooled exciter unit into its housing after balancing.

Regardless of the age or condition of your brushless exciter(s), NEC engineers can discuss your maintenance needs and expectations. With this information they will work out an appropriate schedule and implementation program that will provide you with the high level of reliability synonymous with NEC aftermarket services. From simple maintenance and testing programs to complete AC exciter rewinds and restacks, NEC has the skills and resources to meet your needs.

A typical scope of work is shown below: Bearing clearances to the journal and shaft seals measured; re-babbiting or machining of bearings scheduled if needed Components, including diodes and fuses, cleaned, tested, bagged and labeled; parts replaced as needed Heat sinks inspected and tested; insulation replaced as needed

  • Armature cleaned; winding inspected and tested; replaced or repaired as needed
  • Banding and phase lead risers inspected and replaced as needed Field poles cleaned, inspected, tested; replaced or repaired as needed. Brittle or damaged pole to pole connections replaced PMG stator and armature cleaned; connection wiring inspected and replaced as needed
  • All internal skid wiring inspected and tested; frayed, cracked or brittle wires replaced Operation of ground detector solenoids verified; all RTDs inspected and tested; replaced as needed. Screening inspected for damage and wear; replaced with non-conductive screening materials Optional balance at rated speed and 10 percent overspeed. Fuse and insulation resistances checked afterward Rotor, stator and base cleaned, degreased and repainted. Unit reassembled with a four-point alignment Entire skid wrapped and boxed for shipment
Experience With Large & Small Exciters
NEC has extensive experience with rotating rectifiers ranging from the largest hydrogen-cooled and skid mounted brushless exciters to the smaller shaft-mounted types.
Brushless Exciters Need Balancing
Dynamic balancing is a must for brushless exciter units. Any one of the numerous rectifier components could affect the unit's balance at running speed. Turbogenerator rotors with shaft-mounted excitation are also balanced with these components in place as a unit.
Services for Static Excitation Systems
NEC also refurbishes the slip rings, commutators and brusholders for static exciters.