2 Speed 2 Wind Motor Won't Cold Start After 9 Months in Full Operation 2

[GrimesFrank]

Could use some 3rd Party Expertise please.
New motor replacement for 30yr application (Circ Pump LP/HP); 60 Hz, 575V, 13.3/40 HP, 1200/3600 RPM, 17.5/37.4 FLC, Wye Motor
- In 30yr nary an electrical issue; only bearing failures.
- New motors run for ~9 months then 1200 RPM won't cold start; gets to ~100 RPM before O/L kills. Loud electrical noise (screech not hum)
- Can run with bump from 3600 RPM. No loud noise just normal starting harmonic.
- Cold Start has balanced Voltage/Current as measured by Baker/Meggar Explorer Dynamic @ motor (490 V RMS ph-ph and 45A RMS ph)
- When bump started; Starting voltage dips to 305 V RMS ph-ph but and SS(s) @ 340 V RMS ph-ph.
- When bump started; Starting current maxs at 34A RMS ph and SS(s) @ 2.4A RMS ph

I have a bit more data from the Explorer but I don't want to influence opinion. My rudimentary reading has formed an opinion but would like to hear from all.
What are your suspicions, can we expect 3600 RPM to fail too, what physically would you inspect and finally are there specific tests you would perform to confirm suspicion?

Thanks.

Today is gone. Today was fun.
Tomorrow is another one.
Every day, from here to there,
funny things are everywhere. ~'Dr.' Theodor Geisel

 

[electricpete]

I have come back to find out it has "intermittently" failed to cold start.

If you revisit my discussion 16 May 23 14:53, the only thing the slot combination could not explain was the initial report that this seemed to be a degrading condition. So this new info reinforces the opinions I expressed 16 May 23 14:53. Namely it's a slot combination-induced spatial harmonic problem (scenario 2). It may or may not be accompanied by rotor degradation before (scenario 1) or after (scenario 3). In order I'd rank most likely scenario 2, then less likely 3, then least likely 1.

If it were a simple degrading rotor, you would have other symptoms like pulsating noise and vibration while carrying load. The speed would be lower than expected while carrying load. You probably would have more problems starting in high speed than low speed (And of course as discussed we expect slot related problems to affect only one speed, unlike simple rotor bar degradation). During start it would not jump immediately to 150-200rpm and then stay there (it would be slow from the get-go... it might end up stalling wherever it met the load torque but it would be quite a coincidence to stop at 150-200rpm speed band... where right in the middle is 171rpm =1200/7 which is the most commonly mentioned frequency for spatial-harmonic cusps).

[to edison]Are you sticking with your previous claim that problematic rotor/stator slot combinations do not depend on speed (15 May 23 14:06), or have you revised your position on that?

EDISON - It's interesting that you keep posting your random rotor photos, but you ignore the question directed specifically to you. Let's recall you "corrected" me in this matter. It would be common courtesy to me to admit if you were mistaken on that "correction". It would also be common courtesy to the entire thread audience to acknowledge when/whether a contradiction that you introduced into the thread has been resolved. It is not a random piece of trivia of no consequence to the thread ( It could explain why the problem only occurs in slow, and it might also be relevant to explaining how the problem arose to begin with as Lionel suggested in rewinding an existing motor for multiple speeds without considering slot combinations)

 

[electricpete]

Trying to decontam motor

It seems we work in the same industry / sector.
thread466-211053