10 MW Synchronous Generator Cleaning

We have a large 10 MW 6600 volt synchronous generator that was rewound in 2016. Lube oil was leaking inside the generator from DE bearing which caused a dirty winding. We performed a megger test (5 KVdc - 1 min ) and all readings were good and more than 2G ohm.

  • What is the effect of operating the generator in this case?
  • How can we clean without dismantling the generator? (We do not have the ability to pull up the rotor shaft from the stator.)
  • Which solvent we can use ?

Below is a photo:


2016 NFPA 70B Recommended Practice for Electrical Equipment Maintenance (2019 is published, I have not seen it yet - I suspect little difference in this area)
Chapter 25, Rotating Equipment recommends using a cleaning solvent.

Alstrom generator maintenance manual recommends using “white spirit” (Yep, turpentine - paint thinner). And don’t let the solvent soak into the windings.

Most of the techs I work with like CRC Electro-Clean. After a wipe down (as recommended by Edison and Bill, they will get a case of the CRC, spray, wipe, meg after dried.

Considering the capital investment was $10M - $20M, I highly recommend getting out the mfg maintenance manual and following their recommended procedure - really, that first.

All the maintenance specs say oil contamination degrades the insulation. It needs to be cleaned up.

Personal opinion:
As said, wipe up all you can.
Spray solvent and wipe the rest.
Thoroughly dry and meg before putting into service

Above is a snippet.