Disastrous trafo failure in Russia 15

[edison123]

BBC reports

At least 54 people are missing after an explosion at Russia's largest hydro-electric power station killed eight workers, investigators say.

The accident at the Sayano-Shushenskaya power station in Siberia happened when an oil-filled transformer exploded in a turbine hall, they added.

This damaged the wall and ceiling of the turbine hall which then flooded.

http://news.bbc.co.uk/2/low/europe/8204860.stm

Aren't oil filled trafos banned in the generator/turbine halls to eliminate exactly this type of disaster ?

 

[wolf39]

Keith:

So-called "stoplogs" are installed at the intake of every single penstock. These stoplogs are sort of steel plates which are dropped in front of a penstock intake, thus sealing the penstock. Similar devices are available downstream of the turbine outlet.

Regards

Wolf

http://WWW.HYDROPOWER-CONSULT.COM

 

[edison123]

Keith

They have emergency shutters called stop-logs in the upstream of water conducting system for such eventualities.

Five years back, I was personally involved in a 50 MW generator under stator rewind by us, when the stop-logs failed suddenly. Fortunately, my team had left the work site for the night. The turbine and the intermediate shaft started turning along with our work platform mounted on top of this shaft, no bearing oil was available and it took the power station more than 30 hours to repair the stop-logs ans stop the water.

By that time, the bearings were cooked, the intermediate shaft with the thrust runner got damaged, the upper bracket got cracked. Our work platform was totaled. Luckily no fatalities. It took two more years for the power station to bring back the unit.

From that time onwards, we insist on removing all the rotating parts in the generators we work.

 

[jan63]

one possible cause can be the water hammer developed in the penstock due to sudden load rejection,Normally there are relief valves for relieving the water hammer.A transformer explosion inside the gen.hall will mean a damage to the gen.If a vertical shaft gen.the turbine will be one floor below and then a damage of transformer will not cause flooding.Only detail studies can reveal cause of damage and specially the flooding.Loss of life is regretable.

 

[wolf39]

Edison:

Your team was lucky not to be at site under these circumstances. On the other hand: Had the intermediate shaft been removed in your case, there would have been most likely no guide bearing left to center the rotating parts. And without thrust block the turbine runner couldn't have rested on "solid ground". Can you imagine what would have happened then? Your team may have escaped in time but the power house propably would have been flooded.

A stoplog failure is the worst case accident in a hydro power plant.

Regards

Wolf

http://WWW.HYDROPOWER-CONSULT.COM

 

[edison123]

Keith

You can see the stop-logs in this BBC graphic (named as control gate here)

http://news.bbc.co.uk/2/low/europe/8209663.stm#map

Hi Wolf

I don't ever again want to be involved either of the scenarios (turbine with shaft or turbine without shaft).

Once in a lifetime is fine with me.

 

[itsmoked]

Thanks wolf39 and edison123. That has got to be a really bogus situation when the stop log can fail.

At a plant I toured they had a eight foot ball valve in front of the turbine. It was run with a hydraulic ram that was immense. As the arm that connected to the ball was run down, a huge eye moved down a stud that was about a foot in diameter. Once the valve was closed they would crane a nut onto the stud and spin it all the way down the ten foot stud. I'd probably feel safe below that.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[marks1080]

In a hydro set up this big it takes only seconds to flood the entire plant. I once worked at the 2nd largest underground hydro plant in the world (I believe the one in russia is the biggest). We had a 'safe' room underground where in case of emergency the workers could get into and giant steel doors would seal them off. People often joked about this because if there ever was a major failure the plant would flood before the doors would be able to close.

Also, in the plant I worked in there was a catastropic failure of one of the main output (13.8/230) transformers years ago. The damage can still be seen (huge gouges in the rock wall) but the failure of the trafo did not result in a failure of the plant or genny connected to the trafo.

I have a feeling there might be several causes for the huge amount of damage here. It looks like the unit connect to the transformer must have been obliterated.

 

[ScottyUK]

In the event of a fault on the generator bus the machine speed will suddenly increase. How quickly can the governor or trip valve on a hydro machine cut off the water supply to prevent a catastrophic overspeed?


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[marks1080]

the stop logs are slow moving. even if they were fast i would imagine the water already in the penstocks of a plant that big would be enough to flood the plant. I would guess that the surge chamber would flood first unless one of the gennys blew up. maybe the trafo blew -> genny started over speed and then something happened to blow it to bits...

 

[slavag]

Wolf:
"One possible cause of this terrible accident was a rupture at or near the turbine spiral. From looking at the pictures available it seems that the top generator bracket is lying away from the generator itself, after being lifted by the water stream and pushed aside. The transformer failure most likely followed this incident."

According to not official data, you are right!!!!

 

[waross]

In the video posted by alehman and others at

http://news.bbc.co.uk/2/hi/europe/8206998.stm

You can see enormous surges of water destroying the turbine hall. Over to the right you can see a electrical flash. The water starts first. Looks like a massive failure of the penstock or scroll case.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[wolf39]

In the event of a serious generator fault the unit is electrically disconnected from the grid by breaker action. This is resulting in a unit overspeed. The turbine governor steps in at once but the closing speed of the turbine wicket gates is limited, otherwise the water column in motion would result in an unacceptable penstock pressure increase. We must congratulate the staff that they were able to seal the penstock.

Overspeed-wise the generators and turbines are designed to withstand the so-called run-away speed, which for units of this type are in the region of 80% above rated speed. If - as in this case - the generator rotors are still in motion and all of a sudden being flooded, the resulting hydraulic forces are extreme. One of the videos emerging in YouTube shows a generator rotor, still looking quite intact but the stator, which was surrounding the rotor, is completely gone.

Regards

Wolf

http://WWW.HYDROPOWER-CONSULT.COM

 

[rasevskii]

In view of what other information has already been posted it would seem that the two units which failed disastrously were subjected to a full load rejection due to a fault or disturbamce on the 500 KV system. The resulting guide vane closure caused first an overpressure beyond the design value, resulting in a burst at the scroll case or lower penstock.

It seems these are not steel but reinforced concrete constructions, possibly deteriorated.

It could be that the unit gate openings were over-opened to increase output. This is possible if the gate limiter settings were set beyond the values set at the original commissioning. The generator temperatures being monitored, and if operation was near zero MVAR such a trick is possible on these probably overdimensioned units.

At the time of loss of load, the burst occured, carrying away all the control and protection, the station service AC, and the DC system also. Therefore the generator breakers on the 500 KV side did not trip, resulting in the unit transformers remaining connected to the 500 kV system, with effectively a dead short circuit on the generator side, resulting in the later explosion.

Having been involved in water turbine governors and commissioning of hydro plant, This would be my assessment, further to the assessments of Wolf39 with which I agree.

These units are rated at 640 MW 15.75 KV with two parallel
stator windings. I assume no breaker was between the generator and transformer. Is this actually the case?

It can be that the governor settings had been changed from the original ones or that new equipment had been installed.

I was recently involved with a similar plant which was Russian built.

regards, rasevskii

 

[wolf39]

Rasevskii raised a point. From a Google maps satellite picture one can see 10 penstocks (feeding 10 generators) and 5 main transformer banks, installed outdoors between dam and power house. Each transformer bank consists of 3 single phase transformers, i.e. each transformer bank is fed by 2 generators. If there is a fault on the transformer side, two generators trip and go to overspeed simultaneously. This scenario would mean that a transformer fault was the primary cause of the resulting unit overspeed and failure of hydraulic components.

If the other 8 units were running at the time the power house was flooded, certain damage to these units must be expected as well. Re-commissioning after repair can only be initiated after the cause of this accident has been examined thoroughly. This can take time.

BTW: The generators are equipped with very effective direct-water cooled stator windings. Overload conditions therefore may have been present.

Regards

Wolf

http://WWW.HYDROPOWER-CONSULT.COM

 

[slavag]

Yep, this reason is possible too.
Please take in account, last 5-6 years one company provide retrofit of hydro control systems.

 

[itsmoked]

rasevskii; Welcome to Eng-Tips.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

The complete rotor seen reposing in a hole in the concrete may be an exciter or smaller auxiliary generator.
In other pictures there was a spider with salient field poles, the radius was much greater than the thickness. Another picture showed a similar spider from which the field poles had been stripped.
I cannot now find the picture with the field poles intact online.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rasevskii]

Yes it would appear that the other units have been flooded out to about the level of the lower part of the stators. In any case the turbine guide bearings, the main thrust bearings and a lot of LV panels,motors, etc have been damaged even on any unit that was not running.

In this case it will not be so easy to start up the other units. Flooded out electrical equipment usually is easier to replace than to repair.

I am sure that a large army of contractors, equipment suppliers, personell from other stations, etc will soon mobilize to the site to get the remaining units operational.

As Wolf39 pointed out, there was one trafo bank for two units, therefore there had to be a generator CB for each unit on the 15kV side.

rasevskii

 

[alehman]

Did anyone else notice on Google Maps that the roof of the generator hall is a darker color over the area almost exactly corresponding to the portion that was destroyed? Probably just a coincidence, but I wonder if there had been other recent work in that area.

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[waross]

Not to do with the turbine hall, but possibly pertinent:
From:

http://www.penetron.com/newsletter/apr06/penetron_apr06.htm#sing

CASE STUDY - Dam Focus
SAYANO-SHUSHENSKAYA HYDROELECTRIC POWER STATION, Russia
Sayano-Shushenskaya is the biggest hydroelectric power station in Russia and features the third largest dam in the world. The dam is 240 meters high and 900 meters wide. It has a capacity of 6400 megawatt.
The project faced a typical problem; severe deterioration of the steel reinforcements in the concrete.
Uralpromservice, Penetron distributor in Russia, came up with a detailed repair proposal and won the tender.
Since then, the Penetron system has been used extensively on this project; in 2004 the powerhouse cable sections were repaired, in 2005 major work was done on reinforced concrete elements throughout the project and 2006 will continue to see Penetron repairs on various sections of this project, including the flood-gates.

Bill
--------------------
"Why not the best?"
Jimmy Carter