Rotor Maintenance, Repairs & Overhauls

The ability to manufacture new rotor windings and insulating materials and machine retaining rings in-house, makes NEC a one-stop solution for any rotor project.

National Electric Coil has developed proven solutions for a number of generic design issues discussed in various OEM TILs and OMMs. These problems can be unique to machines of a certain age or to those made by specific OEMs. To name a few on a long list, these include:

  • rotor dovetail cracking
  • rotor turn insulation migration
  • retaining ring stress corrosion
  • J-strap fatigue
  • pole-to-pole crossover cracking
  • top turn cracking
  • brazed joint cracking
  • ground failures
  • lead failures

With our experienced engineering team, we have been able to provide our customers with timely solutions to these and other problems, with no sacrifice of quality workmanship or machine reliability.

Rotor Flux Probe Test

With peak values of no more than 1 mil, NEC leads the industry in balancing your rotor down to the lowest possible vibration levels. NEC's engineers and skilled technicians also are experienced with all aspects of troubleshooting rotor balance problems, including running shorts. The photo at the left shows a large turbogenerator rotor undergoing a flux probe test. The rotor is spinning. The flux probe is located in the red cylinder hanging above the rotor.



Below is a summary of various features and pit capabilities.

  • Ability to accommodate rotors up to 45 feet long
  • 30-, 50- and 85-ton cranes for pit service
  • Rail-guided transport dollies for the larger rotors above crane capacity, up to 100 tons
  • Large inventory of bearings and stub shafts to fit nearly every rotor
  • SCR Digital Drive System and 4000 HP drive train motor
  • System redundancies and 24/7 availability
  • Proven track record balancing large three-bearing rotors, as well as, exciter assemblies

Various testing functions are also possible while the the rotor is in the balance pit.

  • Overspeed testing at rotations up to 3960 rpm
  • Running electrical tests for Insulation Resistance, Impedance and Flux Probe
  • Rotor Thermal Sensitivity Testing, including performing Heat Runs and locating Running Shorts
  • Absolute Vibration Monitoring System for detection of shaft vibration
  • Seismic probes for bearing and pedestals

NEC's balance facility is one of the few in North America capable of performing thermal sensitivity testing. Rotors can be heated up to 80°C above ambient temperature allowing tracking and plotting of changes in vibration, from cold condition to hot.

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