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Induction,jbartos, weak coil wraps were certainly checked for when we found the motor had failed. This was also a concern we had. But on inspection we could not find any bad wraps. Henkv

Location was 40 cm into the slot, from the side of the iron, sorry for the confusion. So firmly fixed. Startup is current limited and no load, so we don't see these high forces in the slot or outside the slot. On inspection after the failure, we checked for both moisture and corrosion, but...

Induction, You are right in saying to not only to depend on the water. Actually we are having an outage soon where the water system will be down and then we will use the space heaters. The motors are TEWAC with the coolers sitting on top of the motors and we use chemically treated water to...

Electricpete: Yes the air is forced through the cooler into the motor. Unfortunately the weather here in Holland is not that warm so 27 C is always a couple of degees above dewpoint. And yes we have checked this on the RTD's. The water is used for cooling lots of installations and is designed to...

Coils of this motor have both wire insulation and 2 layers of mica tape turn insulation. After long discussion, decision was made to replace whole stator and not rewind. So we eliminated the risk of finding damages to the iron package. When inspecting with a boroscope through the ventilation...

We do have a plan in place where we will test the rest of the stator both electrically (surge, PI, PD) and then mechanically to see if we can find root cause. So we will have a comparison with other "first" coils to see if they have aged more than average. But we are interested to find...

Induction, could you please explain what a vandergraf roller is? I don't think ours is. This motor drives a so-called 4-high mill through a 1:2 gearbox. We do use the Baker surge tester. Will look into the high freq wire, but I know that the wire for this motor has been insulated for surges...

Thanks for responses all. -Motor is part of a steel rolling facility with a load cycle of say 3 mins full load, 6 mins idle mode(15% speed, 5% current, power factor ??)It is a 12 pole motor running at 170 rpm nominal speed. -Inspection after failure showed no moisture. Some contamination was...

Recently we have had a ground fault in the stator of a 11MW synchronous motor. A condition measurement(PI,PD, surge) 1 month before the event showed no indication of deterioration. The motor is directly powered by a VF drive.Cable length is too short for voltage doubling. Measured rise times do...