Synchronous Generator PMG Rotor Damaged

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Discussion Overview

The discussion revolves around the issues faced with a synchronous generator, specifically regarding the damage to the PMG rotor after a large load was applied. Participants explore potential causes for the increased vibrations and subsequent tripping of the generator, as well as the condition of the rotor magnets.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes the generator's specifications and the circumstances leading to the damage, noting that the excitation voltage increased significantly when a large load was turned on.
  • Another participant questions whether the generator was a three-phase unit and if the load was balanced, suggesting that an unbalanced load could lead to different vibration patterns.
  • Some participants propose that the gradual increase in vibrations indicates that the issue may not be related to the load, speculating that the damage to the magnets could have occurred progressively.
  • There is a mention of the PMG pole cap fasteners being under-tightened, although it is noted that there are no visible cracks on the pole cap itself.
  • A participant raises the possibility of a loss of synchronism event, suggesting that such an event could lead to extreme power swings that might be misinterpreted as vibrations.
  • Several participants inquire about the availability of instrument recordings to better understand the events leading up to the damage.

Areas of Agreement / Disagreement

Participants express differing views on the cause of the vibrations and the damage to the rotor magnets. While some suggest that the load is not the issue, others propose various hypotheses regarding the generator's operation and condition. No consensus is reached on the exact cause of the problem.

Contextual Notes

There are unresolved questions regarding the relationship between the load and the generator's performance, as well as the implications of the PMG pole cap fasteners' tightness. The discussion also highlights the complexity of diagnosing issues in synchronous generators with both permanent magnets and internal excitation systems.

vish1711
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TL;DR
Synchronous Generator PMG Rotor Damaged
Generator - 1800rpm, 11kV, 656A. While running Gen, a large load was turned on, and excitation voltage went from 23V to 120V, but that's a normal situation that happens every time and on all Generators. But this time after turning on the large load, vibrations started increasing, and Gen tripped on high vibrations. When inspected PMG rotor magnets were broken inside the gen. We did all the testing and couldn't found anything. Does anyone has experienced a similar thing before?
 
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Welcome to PF.
Was it a 3 phase generator? Was the heavy load a balanced 3 phase load?
Did one of the three phases break due to load before the other phases?
 
vish1711 said:
Summary:: Synchronous Generator PMG Rotor Damaged

But this time after turning on the large load, vibrations started increasing,
If the vibrations increased gradually, the problem is probably not with the load. Perhaps one magnet cracked, then another, then another. If the load was unbalanced three phase, the vibrations would be a step, not a ramp.

Do you have recordings of what happened from the instruments?

I am not familiar with synchronous generators that have both permanent magnets and external excitation.
 
anorlunda said:
If the vibrations increased gradually, the problem is probably not with the load. Perhaps one magnet cracked, then another, then another. If the load was unbalanced three phase, the vibrations would be a step, not a ramp.

Do you have recordings of what happened from the instruments?

I am not familiar with synchronous generators that have both permanent magnets and external excitation.
It was balanced three phase load and started with 3 Generators. Other two Generators did handle the load very well. And it's not external excitation system. There is a exciter system within the generator. You are right, it has nothing to do with the load I guess but I can't see any reason of damaging magnets. All electrical and magnetic tests were fine.
 
Baluncore said:
Welcome to PF.
Was it a 3 phase generator? Was the heavy load a balanced 3 phase load?
Did one of the three phases break due to load before the other phases?
Baluncore said:
Welcome to PF.
Was it a 3 phase generator? Was the heavy load a balanced 3 phase load?
Did one of the three phases break due to load before the other phases?
It was balanced three phase load and started with 3 Generators. Other two Generators did handle the load very well. It has nothing to do with the load I guess but I can't see any reason of damaging magnets. All electrical and magnetic tests were fine.
 
vish1711 said:
Summary:: Synchronous Generator PMG Rotor Damaged

Generator - 1800rpm, 11kV, 656A. While running Gen, a large load was turned on, and excitation voltage went from 23V to 120V, but that's a normal situation that happens every time and on all Generators. But this time after turning on the large load, vibrations started increasing, and Gen tripped on high vibrations. When inspected PMG rotor magnets were broken inside the gen. We did all the testing and couldn't found anything. Does anyone has experienced a similar thing before?
PMG Pole cap Fasteners were tighten less than 20 Nm whereas it should be between 35-37 Nm. But still there is no crack on Pole cap but magnet under the pole cap are damaged.
 
How about a loss of synchronism event? After loss of synchronism, as frequency departs from synchronous frequency, you would see extreme and wild swings in power. When the frequency difference became big enough, those swings might be interpreted as vibrations.

I ask again. Do you have records from the instruments?
 

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