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Cutting out damaged coils from large, low-speed machines

An emergency repair to keep your customer operating with minimal disruption

  • June 2010
  • Number of views: 3723
  • Article rating: No rating

Chuck Yung
EASA Senior Technical Support Specialist 

Historically, one emergency repair used for large, low-speed machines (motors as well as generators) was to remove the damaged/failed coils from the circuit. Cutting out a single damaged coil permitted the machine to be quickly returned to service with minimal disruption.

As long as some basic principles are followed, this method can be safely used. It is still popular with operators of large, low-speed synchronous ma­chines. One common application for such machines is hydro power stations. There are many old hydro generators operating with a dozen or more coils bypassed. The underlying goal when cutting out coils is to minimize the negative side effects and keep coil groups intact for future removal.

WARNING: This procedure is not recommended for 2-pole machines. The odds of success are slim.

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EASA Technical Manual

More information on this topic can be found in EASA's Technical Manual
  • Section 2: AC Machines

Related Reference and Training Materials

Principles of Medium & Large AC Motors (NEMA Standards)
  • Section 7: Stators

Principles of Medium & Large AC Motors (IEC Standards)
  • Section 7: Stators

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