15MW Steam Turbine Generator coupling Breakdown
15MW Steam Turbine Generator coupling Breakdown
(OP)
Hello Everyone,
Hope everybody is doing great in this forum.
I am right now working on a commissiong of a 15MW steam turbine generator and have some questions for you guys to answer
I represent the customer who bought the generator unit.
While we were commissioning this generator two weeks before, we had an incident where the coupling broke due to wrong synchronization(or atleast we think-investigation still going on). But the project is proceeding and we have shipped the generator to the factory to check its integrity
I am schedule to go to the factory to inspect and monitor the testing process and report back to the customer.
Do you guys have some checklist where i should be focusing and looking for damages in the generator. This is the first time i am going to the generator factory.
BACKGROUND.
The generator was almost commissioned and was synchronized to the utility.
The night before the incident the generator was set to output 10MW and it ran for the whole night
The next morning we were going to check an EStop circuit and Auto synchronization function
So, we had to trip the unit and so we gradually reduced the output of the generator
We brought it to 500KW and ready to trip
But the Hyndai representative wanted to do some final point to point checks on the wiring diagrams
We they were doing this we heard sudden noise and the next thing we know, the coupling at the Turbine-Gear box end was broke.
The emergency lube oil circuit was broke and oil was splattered all over the place
But the Turbine and the generator rotate atleast for 3 minutes after the coupling broke. The vibration monitors did go to the alarm stage but never to a trip level state.
When we questioned the Turbine and Generator representative, they would not give us any answer as they claim the investigation is going on and they wont be able to issue a statement until their underwriters are given one
We questioned the Electrical Technician who helped the Hyundai Generator Engineer and he claims that the Hyndai guy had him bypass the sync check relay.
Now i have two questions:
What do you guys think would have happened here.
What would be the worst case damage to expect. When i got the inpsect the factory testing what should i focus on? What could have gone wrong as far as the generator is concerned- Shaft? End winding? rotor? Stator?
I would appreciate any insights and advice i can get from experts like you people.
Thanks
gokul
Hope everybody is doing great in this forum.
I am right now working on a commissiong of a 15MW steam turbine generator and have some questions for you guys to answer
I represent the customer who bought the generator unit.
While we were commissioning this generator two weeks before, we had an incident where the coupling broke due to wrong synchronization(or atleast we think-investigation still going on). But the project is proceeding and we have shipped the generator to the factory to check its integrity
I am schedule to go to the factory to inspect and monitor the testing process and report back to the customer.
Do you guys have some checklist where i should be focusing and looking for damages in the generator. This is the first time i am going to the generator factory.
BACKGROUND.
The generator was almost commissioned and was synchronized to the utility.
The night before the incident the generator was set to output 10MW and it ran for the whole night
The next morning we were going to check an EStop circuit and Auto synchronization function
So, we had to trip the unit and so we gradually reduced the output of the generator
We brought it to 500KW and ready to trip
But the Hyndai representative wanted to do some final point to point checks on the wiring diagrams
We they were doing this we heard sudden noise and the next thing we know, the coupling at the Turbine-Gear box end was broke.
The emergency lube oil circuit was broke and oil was splattered all over the place
But the Turbine and the generator rotate atleast for 3 minutes after the coupling broke. The vibration monitors did go to the alarm stage but never to a trip level state.
When we questioned the Turbine and Generator representative, they would not give us any answer as they claim the investigation is going on and they wont be able to issue a statement until their underwriters are given one
We questioned the Electrical Technician who helped the Hyundai Generator Engineer and he claims that the Hyndai guy had him bypass the sync check relay.
Now i have two questions:
What do you guys think would have happened here.
What would be the worst case damage to expect. When i got the inpsect the factory testing what should i focus on? What could have gone wrong as far as the generator is concerned- Shaft? End winding? rotor? Stator?
I would appreciate any insights and advice i can get from experts like you people.
Thanks
gokul





RE: 15MW Steam Turbine Generator coupling Breakdown
What event history do you have from the turbine controller and the protection? A well-configured Historian on the turbine and generator control system is the best window you can have into what took place - I hope the OEM took the time to configure it, otherwise the investigation could well descend into speculation and finger-pointing.
Worst case damage? Broken coupling or bent shaft, possibly damage to the long LP turbine blading, perhaps damage to the stationary vanes if they have been hit by the blades. Perhaps bearing damage - a wipe is certainly possible as the rotor was thrown about. The vibration data is a positive sign that you may have been fairly lucky, in as far as broken coupling is 'lucky'.
Look for endwinding movement and loose stator blocks, on the rotor look for copper movement under the endbell and signs of a rub anywhere on the bearings or fans. It would be useful if you could perform an RSO on the rotor to identify any anomalies.
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If we learn from our mistakes I'm getting a great education!
RE: 15MW Steam Turbine Generator coupling Breakdown
Forgive my ignorance but i do not know what is RSO means. If this is a test done on rotors then, i should inform you that this generator in discussion is a Permanent magnet Brushless generator. So can a RSO be done on this type of rotor too?
I too came to the exact conclusion on what may have happened. But regarding the auto synchronizer the synch selector switch was in the manual mode.
I have the event history from the SEL 300G relay which i downloaded and have attached. But i do not have anything from the Turbine PLC. They barricaded the whole area and the whole panel is switched off now.
I am also counting on being lucky.. but for record, the turbine rotor has been sent to the factory for inspection and repair.
I am schedule to go to the generator factory next week monday when they start tearing apart the generator. Thanks for you suggestion and locations where i need to focus. Is there any test that i should require those guys to perform on our generator that would prove the integrity of my generator?
Thanks again.
gokul
RE: 15MW Steam Turbine Generator coupling Breakdown
Sorry to say this, but it is absolutely irresponsible to allow anyone to be doing any wiring or "point to point checks" when the unit is running online or even if it running at all. By point to point checks what is meant? Was someone using a megger or bell tester or putting grounds or voltage here or there in the control wiring? Unbelievable. All panels and related equipment must be locked up or secured so that no one, NO ONE, goes in and does anything of this sort. Wiremen and cable terminators have to be ordered out of the operating parts of the plant.
It was bad management of the commissioning that was at fault. Not a uncommon problem on sites where many different contractors and suppliers are present.
Introduce proper lockout/tagout procedures. If there is no cooperation or respect for the procedures, the job has to be stopped.
Otherwise someone may get hurt next time.
rasevskii
RE: 15MW Steam Turbine Generator coupling Breakdown
rasevskii
RE: 15MW Steam Turbine Generator coupling Breakdown
rasevskii's comments about the poor control of the area are very fair. If the OEM's engineer requested that the check-sync relay be bypassed then he will have some explaining to do. I expect he is denying that he said such a thing, but it would be interesting to know what he was trying to do.
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If we learn from our mistakes I'm getting a great education!
RE: 15MW Steam Turbine Generator coupling Breakdown
I am not familiar with the format of the data file that you attached to your 2 Jun 11 15:33 post but, I am good with numbers and this is what I see:
http://ww
The voltage is shown to be in kV. VAB and VBC show no voltage. This would indicate a fault in the 'B' phase.
I am thinking that the current readings are secondary current from a CT such that 5 amps equals the CT rating. I do not know the convention that is being used. I assume that a positive current is power out of the generator and a negative current is power into the generator.
Regardless of the current/power flow convention, I see that there is a significant ground current that is 140% of CT rating. There is also power (current) going both ways (in and out of the generator) in the phases and significant currrent flow in the neutral.
This is a total guess because I only have the information that is provided in the thread but, I think that a generator stator ground fault is indicated. Other possibilities include a ground fault failure in the leads between the stator and the circuit breaker.
This is the cause of the broken coupling and any subsequent damage that resulted from the transient torque caused by reclosing after trip without synchronization.
The good news is that you have this data file that recorded the event. A person who is familiar with this format should be able to tell EXACTLY what happened. I would recommend that your company hire an Expert and a Lawyer to begin an investigation on your own.
This is because I am assuming that there are major costs associated with this event and, in the end, somebody has to pay...
RE: 15MW Steam Turbine Generator coupling Breakdown
While i agree that we should have not allowed nobody to do any check while the machine was running.... we had absolutely no idea the sync check relay was bypassed. I am not trying to defend myself here but just trying to provide more information. He was supposed to be the expert and in many cases we are compelled to go by what he requires.
Yes, as you suggested, the gearbox is already on its way to the manufacturer for inspection and repair.
We are also getting statement from whoever was there on sight and getting our lawyers involved in this matter.
Thanks for your comments. It never offended me but proved how safe you are. We were taking all kinds for safety measure when we first synchronized this machine... Thanks again
Scotty,
Thanks for the information. I will request the generator guys to perform the RSO on the rotor. Thanks again for the valuable information.
RE: 15MW Steam Turbine Generator coupling Breakdown
At the beginning of the event, the breaker is open and there is no current.
At relay time 10:46:12.250 in the event everything changes with the breaker closing. Way out of phase closing.
At relay time 10:46:12.246 VAB has a positive maximum. At relay time 10:46:12.251 VAB is at -6.5kV, about 108 degrees later. The next data point, relay time 10:46:12.252 (16 samples per each 60Hz cycle) VAB is 1kV rather than the expected (from prior cycle) -10.8kV. The first VAB negative maximum happens at relay time 10:46:12.257 (0.6875 cycles after the positive maximum). That extra 0.1875 cycles equates to 67.5 degrees.
The voltage collapses sufficiently that the instantaneous undervoltage element (supervised by 52a) trips the breaker as soon as the 52a contacts indicate closed.
The first positive peak of C phase current reaches 10082. This is a filtered 60Hz fundamental value and is the highest current seen. The actual peak would require a raw event have been downloaded from the relay.
Ugly, ugly, ugly. Shocked the he!! out of the machine.
RE: 15MW Steam Turbine Generator coupling Breakdown
However, I would like some help in understanding why there seems to be a ground fault current recorded in the data that I quoted above. I am not questioning davidbeach by any means since he obviously knows what he is looking at.
Am I reading the data file wrong? I would think that the ground fault current indicates a stator failure.
DavidBeach, what am I missing??? Can you give a simple explanation so that I can understand what you are seeing?
RE: 15MW Steam Turbine Generator coupling Breakdown
RE: 15MW Steam Turbine Generator coupling Breakdown
Excellent Explanation. Thanks.
I would also appreciate if you have any insights or pointers to look for and catch on the repair on the generator now. As you can see Scotty have given me good information but anything you may want to add might help as well.
Thanks again.
RE: 15MW Steam Turbine Generator coupling Breakdown
You had a bad day, that's for sure. Good luck.
David Castor
www.cvoes.com
RE: 15MW Steam Turbine Generator coupling Breakdown
Dave
David Castor
www.cvoes.com
RE: 15MW Steam Turbine Generator coupling Breakdown
RE: 15MW Steam Turbine Generator coupling Breakdown
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If we learn from our mistakes I'm getting a great education!
RE: 15MW Steam Turbine Generator coupling Breakdown
It was a very bad day..And as our legal guys are saying its going to get ugly as well.
Our folks are working on points to sue for compensation for downtime. Warranty wise it is for me to make sure that my client get the machine in a good condition he paid for.
I will post some pictures once i complete my factory inspection.
This forum has always been an excellent source of information.
Thanks for all those who contributed.
RE: 15MW Steam Turbine Generator coupling Breakdown
I am curious - so need to ask if the generator was a Hyundai Korea unit or Hyundai-Idal unit. I have a local client that has a bid from Hyundai.
RE: 15MW Steam Turbine Generator coupling Breakdown
It is a Hyundai Ideal unit. In all fairness to Hyundai, They are ready to work with us. They were really fast acting and mobilized their crews once the incident happent. If they take care of this issue as it is supposed to be, then i would not have no problems in buying an another Hyundai ideal unit.
Before this incident happen, the machine was so perfect we could hardly get any vibration and noise was next to nothing.
my 2 cents before you take any decisions.
RE: 15MW Steam Turbine Generator coupling Breakdown
With any luck, the coupling acted as a fuse and saved you from major turbine distress, but don't take that for granted. Check for cracking in anything that you wouldn't want to see accelerated suddenly - Scotty mentioned the LP blades - good place to start. Check the dovetail fits at the blade roots as well.
Rotor run outs all up and down its length.
Check the gear box frame. If it was cast you may be OK. If it was fabricated, it might be tweaked.
rmw
RE: 15MW Steam Turbine Generator coupling Breakdown
Very lkely that the jumper over the sync check relay was put in to allow the brkr to be closed during dry testing, but, unfortunately, it was forgotten about.
rasevskii
RE: 15MW Steam Turbine Generator coupling Breakdown
Just thought of giving an update on the findings of the inspection test performed for the benefit of those who are curious...
The stator looked fine... the end windings were all normal and were spared....
But one of our rotor windings was shorted. Further more to our agony the shaft was bowed before correctiive limits.
This has put us in a situation to wait for a whole new rotor to be manufactured... The lead time is 16-20 weeks...
Now, i still cant believe a machine which was jus running at a mere 500KW could have experience this much damage? If that machine would have been running at 15MW would be damages be more than this where it could have caused some catastrophy???
Also, Why was vibrations very low when they rolled down? Anybody could think of any logic behind that??
RE: 15MW Steam Turbine Generator coupling Breakdown
Was there a TIR measurement reported? Generally if you're reading prox probes you'd expect to see at least that much on the prox probes.
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(2B)+(2B)' ?
RE: 15MW Steam Turbine Generator coupling Breakdown
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(2B)+(2B)' ?
RE: 15MW Steam Turbine Generator coupling Breakdown
Bill
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"Why not the best?"
Jimmy Carter
RE: 15MW Steam Turbine Generator coupling Breakdown
RE: 15MW Steam Turbine Generator coupling Breakdown
as for the vibration, if the monitoring is only prox probes, during severe conditions, the bearing pedistal is moving in phase with the shaft and thus the prox will show little displacement
RE: 15MW Steam Turbine Generator coupling Breakdown
I understand that its a out of phase sync issue and so the loading of 500KW is not the influencing factor. But, it is hard for me to disregard that if that machine were to be running at 15MW then, it should have got to have more torque on that shaft. So when the out of sync condition happened it either tried to catch up(acclerate) or slow down(stop or deccelerate) with the utility speed... As i understand this if it had to accelerate it would have had less forces at that higher speed and if it had to decelerate it would have been more catastrophic failure.
Is my understanding right or am i way of on understanding what happen?
RE: 15MW Steam Turbine Generator coupling Breakdown
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If we learn from our mistakes I'm getting a great education!
RE: 15MW Steam Turbine Generator coupling Breakdown
rasevskii
RE: 15MW Steam Turbine Generator coupling Breakdown
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(2B)+(2B)' ?
RE: 15MW Steam Turbine Generator coupling Breakdown
The problem was that while running nicely at 60Hz, it was leading the system by 67.5 degrees and allowed to close in that condition.
RE: 15MW Steam Turbine Generator coupling Breakdown