Synchronous Generator PMG Rotor Damaged

[vish1711]

TL;DR 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?

 

[Baluncore]

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?

 

[anorlunda]

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.

 

[vish1711]

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.

 

[vish1711]

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?

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]

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.

 

[anorlunda]

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?