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Disastrous trafo failure in Russia
15

Disastrous trafo failure in Russia

Disastrous trafo failure in Russia

(OP)
BBC reports

Quote (BBC):

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 ?

 

RE: Disastrous trafo failure in Russia

(OP)
Oil filled trafos are silent beasts.  

RE: Disastrous trafo failure in Russia

"Oil filled trafos are silent beasts."

Tell me about it.  Our local utility company lost one of the 230-34.5 kV 50 MVA feeding my facility a couple of weeks ago in an apparent HV bushing failure.  It was two years old.

They're scrambling.  Fortunately they have a system spare, but we're a couple of weeks from getting it.

old field guy

RE: Disastrous trafo failure in Russia

(OP)
Yipes, two bushings gone... Did they find the root cause ?

RE: Disastrous trafo failure in Russia

Edison--

Our local utility company is being a bit quiet on this one.

As a former employee of said utility, AND a client representative now, I got into the sub and snapped a few pictures.  It appears that the H2 (center) bushing blew out.  The fragments flew fifty meters.  Fragments from H3 fell straight down on top of the transformer.  There was a fire from the arc igniting the oil from two bushings.

Oil samples of the main tank and LTC show no effects from the bushing failure.  Fragment dispersal of the glass oil pot lead me to suspect internal arc within the bushing.

I asked the utility folks if there was any history on these bushings and there doesn't appear to be anything abnormal with them as a group.

The transformer was subjected to the standard battery of tests two years ago during commissioning with no abnormal findings at that time.  Routine DGA is normal, but that wouldn't show a bushing problem anyway.  Post-failure DGA is also normal.

The transformer is less than two years old, and very lightly loaded.  It's been stripped down and trucked back to the factory.

old field guy

RE: Disastrous trafo failure in Russia

Thanks for the inside info Old Field Guy. LPS

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

RE: Disastrous trafo failure in Russia

(OP)
Thanks OFG. Interesting that the main tank oil showed no effects. Is there a history of lightning strikes in that area ?

RE: Disastrous trafo failure in Russia

edison--

Yes.  I am sitting right under a pretty good thunderstorm right now.

However, that transformer failure was at 0530 and no storms anywhere in the broad area.  The local fire department was still cooling things down when I arrived at 0645.

On a happy note, the relays and breakers cleared it in 3.5 cycles.  That's all the voltage dip I saw in the plant.

old field guy

RE: Disastrous trafo failure in Russia

2
"Aren't oil filled trafos banned in the generator/turbine halls to eliminate exactly this type of disaster?"

Oil-filled types are pretty much the only option in the multi-MW class, although I think Toshiba (?) were playing with an SF6 cooled transformer a few years ago.

A sad day for the guys in Siberia.
  

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

RE: Disastrous trafo failure in Russia

Some hydro installations use a cable tunnel to carry the output of the generators to outdoor mounted Generator Step Up transformers. As far as being banned, that would be a local regulatory issue. Possibly code, possibly insurance, possibly both. Depends where in the world.

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

RE: Disastrous trafo failure in Russia

oldfieldguy   - did you happen to power factor the bushings as part of your acceptance tests

RE: Disastrous trafo failure in Russia

Thank you edison for giving this failure detail.It is not understood how the turbine hall got flooded.I was a witness several years back where a hydro station with turbines ,generators and all got flooded as the dam overflowed due to suddeninrush of water in the dam and the
gates did not operate!

1) In hydro-electric stations it is not always  practical to put the generator transformers far away from genertaor hall as the busduct length will go up enormously causing loss and cost.So transformers are put near to turbine-generator hall and switch yard is put some distance away(usually several  metres higher altitude) where space is not a premium.
2)To prevent such catastrophic failures SF-6 filled transformer is a solution( Toshiba made up to 330 MVA 350 KV)but not practical due to cost and size.There are better solutions to prevent such tank exlosion and oil spills.

3) Problems will be more severe in underground power stations where the transformers will be underground.With GIS, even switchyard is also brought underground.

4)Transformer fires and consequent transformer damages are frequent due to failure of oil impregnated paper condenser bushings.One way to avoid is is to monitor the power factor of bushings and remove the same as soon as the PF go to dangerous zones.Better bushings are available today-RIP bushings-Resin impreganted paper condenser bushings which are dry type and fail safely.I hear that in Europe many utilities are retrofitting old critical  transformers with RIP bushings.

RE: Disastrous trafo failure in Russia

(OP)
Looking at the pictures posted later at that BBC site, the transformers were not inside the turbine hall but just outside the powerhouse. Sad that so many lives were lost.

RE: Disastrous trafo failure in Russia

I agree. And the explosion looked too clean (and powerful) to be a transf.  

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

RE: Disastrous trafo failure in Russia

hilotech--

the utility company contracted the testing out.  I have not seen the actual report but I did speak with my former boss there, a man I consider to be honest, and he said the bushing power factors and measured capacitances were within tolerance for new equipment.

i didn't mean to hijack this thread..

old field guy

RE: Disastrous trafo failure in Russia

2

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.

The unit main transformers in question were not installed inside the power house but outdoors, which is common practice. For underground stations unit main transformers are always installed in a separate transformer cavern, away from the machine hall.

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM  

RE: Disastrous trafo failure in Russia

Did someone have any information about the role of transformer explosion in the German Nuclear power station few weeks ago?

RE: Disastrous trafo failure in Russia


dga1960:

The nuclear plant "Kruemmel" has one 1400 MW el boiling water reactor installed with two parallel unit transformers of 27/380kV in operation. One of these transformers had an uncontained winding short June 28, 2007, resulting in a fire.

After comprehensive modification work on the entire plant and after transformer replacement a second transformer winding short occured July 04, 2009. This short was contained and there was no fire. Before re-commissioning a PD measurement on the transformers was scheduled but not carried out.

In both cases the nuclear part of the plant was not effected.

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM   

RE: Disastrous trafo failure in Russia

2
If you have a disaster so bad that it actually pulverizes the generator and floods everything how did they manage to turn off the water? (Pretty amazing really.  Something must've gone right.)

Keith Cress
kcress - http://www.flaminsystems.com

RE: Disastrous trafo failure in Russia


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
WWW.HYDROPOWER-CONSULT.COM  

RE: Disastrous trafo failure in Russia

(OP)
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.

RE: Disastrous trafo failure in Russia

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.

RE: Disastrous trafo failure in Russia


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
WWW.HYDROPOWER-CONSULT.COM  

RE: Disastrous trafo failure in Russia

(OP)
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. 3eyes

RE: Disastrous trafo failure in Russia

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

RE: Disastrous trafo failure in Russia

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.

RE: Disastrous trafo failure in Russia

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!
 

RE: Disastrous trafo failure in Russia

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...

RE: Disastrous trafo failure in Russia

2
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!!!!
 

RE: Disastrous trafo failure in Russia

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

RE: Disastrous trafo failure in Russia


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
WWW.HYDROPOWER-CONSULT.COM

RE: Disastrous trafo failure in Russia

2
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

 

RE: Disastrous trafo failure in Russia


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
WWW.HYDROPOWER-CONSULT.COM

RE: Disastrous trafo failure in Russia

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

RE: Disastrous trafo failure in Russia

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

RE: Disastrous trafo failure in Russia

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

 

RE: Disastrous trafo failure in Russia

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

RE: Disastrous trafo failure in Russia

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

RE: Disastrous trafo failure in Russia

Having read Waross post on the Penetron work, and looked at their site, It would seem that this method only prevents further deterioration of the existing rebar.

We are not civil engineers but the drilling of holes in the concrete to inject the preserving material would in fact weaken the construction initially. Was this a factor?

The two machines that were wrecked were according to the photos not adjacent to each other. There was a unit in between that seemed to remain intact. Was it not running or unloaded only? In this case the load rejections that wrecked the two units involved two transformer banks not one. As wolf39 points out two adjacent? units are on one bank.

If the water flooded out units are in fact recommissioned it may be only at reduced permitted maximum output. However, these being Francis units the minimum permitted continuous load has to respect the cavitation area which may possibly be at, shall we say, less than 70 percent load.
Unless modifications are made. But that is the business of the turbine supplier.

Only some thoughts.

rasevskii




  

RE: Disastrous trafo failure in Russia

Further to this item, note that there are a series of excellent detailed photographs of the damage posted under theoildrum.com, comments, username ++syndroma++ dated on yesterdays Drumbeat, 21 August. Follow the link there to the Russian site which has the photos.

It would appear that the stators of the wrecked units have just disappeared/exploded into small bits/as if electrical forces were involved...The only stator section seen intact is in fact from the auxiliary generator which supplied the thyristor excitation system. Seen in one photo.

Forum members are invited to add their expertise here...

regards, Rasevskii

RE: Disastrous trafo failure in Russia


It would take too much time to comment on all the drumbeat pictures. It is interesting, however, that the status quo of every single unit is documented.

The entire unit 2 is completely wrecked and this unit seems to be the one where everything started. The turbine runner is visible in the generator pit, amoungst all the other rubble. Generator units 7 and 9 are also complete losses, both stators having disappeared entirely. These units seem to have sped up uncontrolled but with the turbines left hydraulically intact. This can be seen from the video of 1:08 duration, where the water column is visible in the unit 2 region only. The roof is gone at this time already but in the region of unit 7 there is some heavy flashing. These flares shine through the front window and may have their origin in generator 7 which propably was still running in an excited mode, its stator winding then failing. All this despite the fact that the machine floor was flooded already. There is room for some speculation here. A failure of the main transformer bank belonging to unit 7 propably can be ruled out as this bank is placed behind the massive back wall of the powerhouse.  

Unit 6 was under repair and not running. It therefore may have been flooded only and is very likely the first one to be operational again. However, the root cause of this accident has to be fully understood before re-commissioning can be initiated.

A video of 0:37 duration is showing unit 9 in the backgroud with a cloud of water spray visible inside the generator pit. It may well be that this unit was still in motion this moment, whirling the water around which was trapped in the generator pit. It must have taken quite a time to have all 10 stoplogs installed.

Is there anybody around who can translate us the Russian comments audible in all these videos?

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM     

RE: Disastrous trafo failure in Russia

(OP)
Thanks Keith for that link. May be some one can answer this.

1. Powerhouse seems to be curved. Is it because of the dam wall ? Wouldn't it make it tougher for a crane to travel in an arc ?

or is it an optical illusion ?

2. I don't see any crane rail on the tailrace side. ???

RE: Disastrous trafo failure in Russia

The track on the tailrace side is probably along the walkway. I believe that there are one or two rails on the back edge of the walkway. The crane bridge will have gantry legs on the tailrace side. With the proper drive ratios side to side, it is probably no harder to run a curved track than it is to keep a crane straight on a straight track.
By the way, edison123, thank you for making the original post.
Thanks also to Keith for the link.

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

RE: Disastrous trafo failure in Russia


Videos are placed in You Tube. Search for "Sayano Shushenskaya".

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM

RE: Disastrous trafo failure in Russia


The "Blog post" issued by Syndroma on August 21, 2009 at 1:03 pm (see for rasevskii's post dated August 22, 2009, 07:33) show some penstock pictures. These penstocks consist of large diameter steel pipes, encased by concrete. The surface quality of this concrete looks poor and one can only hope that the steel pipes under the concrete look better.

The power plant staff has undoubtedly done an heroic job by sealing the 10 penstocks inmidst of all the chaos. God bless them.

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM

RE: Disastrous trafo failure in Russia

There is nothing interesting in audio of these videos. In that one where they show the HPP during the disaster from the roadside and somebody is running towards the station they say on the back "Look, look, look ! ... May be it is a high time to run away from here... That is the end!" Normal comments of people who are under stress and probabbly still cannot realize the extents of the catastrophe.
Much more interesting are comments in the forum, but they are too long to translate
 

------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant
 

RE: Disastrous trafo failure in Russia

Unfortunately Youtube is blocked at my location here.

A possible scenario/this is speculation/would be as follows-

1. A fault on the 500KV results in a load rejection of all running units, likely nine.

2. Unit 2 is destroyed due to failure of the spiral casing.

3. The resulting flood wipes out all the AC and DC supplies,
that is, vital cables are ripped up. It seems unit 2 is located near the center of the station, oddly.

4. The turbine governors on the other units fail to close the guide vanes or transfer to manual control, as all electrical supply is lost. Assumption is that the units have electronic speed pickups /several/ but no power supply is available. Or possibly were om manual before. See item on load limit settings.

5. The remaining units go to runaway speed and stay there until something fails.

6.The operators manage to close the intake gates/stoplogs/ manually inside the dam after some time eventually stopping the runaway units. The ones not destroyed that is.

7. No electrical protection trips operate/no DC supplies.

8. The 500 KV switchyard /some distance away/ would have its own DC system and protections, these may have operated
partially but some may have been interlocked with circuits in the station whose cables were destroyed.

In the good old days the turbine governor was independent of all outside supply having its own PMG on the turbine shaft. Possibly not the case here. There was likely also no mechanical-hydraulic overspeed tripping device on the turbine shaft, independent of all electrics. A usual feature of old stations before anybody trusted electricity..

regards, rasevskii
 

RE: Disastrous trafo failure in Russia

Babelfish works effectivly on the forum pages "Itsmoked" pointed us to. The results are not perfect by any means, but the basic statements are clear enough. There are a couple of plant employees posting, and dicussion of a governor retrofit, the first starting of a recently repaired unit on that day, etc. Early on, the dialog indicated local news media as saying "hydroshock" was the cause, perhaps by abrupt opening of flow controls somehow.    

   

RE: Disastrous trafo failure in Russia

Some new information can be found on page 170 of the Russian blog, item 3389. Translate this by babelfish.

I would not post this here.

It seems a new governor was being tested and it all went wrong on unit 2. Runaway, then an out of sync closure onto the grid. The rest is history...

Members are invited to read this for themselves.

Scroll down for a model view picture of the units also.

regards, rasevskii

RE: Disastrous trafo failure in Russia

I have some questions as below,

 1. Is there anyone has the single line dia.(w/relay) of this plant?
    Please upload for reference.

 2. How to prevent the disaster like this from the viewpoint of protection and control?

 

RE: Disastrous trafo failure in Russia

Hi.
Please see attached, it's Russian, but photo isn't need comments. History of station and views.
http://4044415.livejournal.com/51285.html

For my pinion we need wait for the some real information.
On this moment, talk about problems in the unit 2 with control. Operation personal start with stop of turbine, but regular stop, not emergency stop and this step in some not stability zone initilizaied crash of system.

RE: Disastrous trafo failure in Russia


I'm at present studying the internet discussion going on in Russia. This is a difficult task as the babelfish translation into English is far from perfect. Still, it is obvious that quite a few of the comments contradict each other and that the posts are all highly speculative. Fact seems to be, however, that unit 2 was decommissioned mid January 2009 for welding repair on the turbine runner and that the turbine governor was replaced. Also, there was an increase of vibration prior to the accident.

Until an official accident report is published we all have to stick to the videos and photographs available. The video of 1:08 duration has been taken shortly after the accident occured. It shows a black cloud of smoke in the vicinity of the collapsed roof behind the machine hall (this is better visible in another video), this propably being an indication of a transformer fault. Then there is some flashing going on behind the machine hall window in the vicinity of unit 7 or 9, lasting for about 6 seconds. About 10 seconds later an air blast breaker bang is audible, suggesting that some power may still have been available in the powerhouse at this time.

At first I was most surprised that the generator stators of units 2, 7 and 9 were gone completely. They seem to have been pulverized. To me there is an easy explanation for this. The generator was running in a pit filled with water. The generator rotor with a circumferrential speed of 80 m/s or more was acting like the impeller of a centrifugal pump. The hydraulic pressure entered the stator core cooling ducts and the lifting force ripped off the nuts of the core pressure bolts. The stator core must have delaminated in seconds and the stator frame then disintegrated and was washed into the turbine pit below or was disposed off somewhere else. In some of the pictures taken early, before the cleaning-up activities started, some stator core laminations were lying on the machine hall floor but most of these may also have been washed into the pit.

Some generator units look quite intact with the top covers still in place. Maybe these covers were tight enough to prevent pit flooding and/or unit speed was low enough already when flooding occured.    

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM  

RE: Disastrous trafo failure in Russia

Agree with Wolf 39.

I am also babelfishing the Russian blog, and on page 262 are interesting diagrams of the governor system as it was newly upgraded.

The turbine guide vanes/aka wicket gates/are positioned by individual oil servomotors which are evidently controlled by a digital system. A discussion about Omron follows. It would appear that each servomotor gets a position command signal and follows that by some kind of comparator mechanical linkage, with electrical feedback.

The turbine pit is not the place for electronics.

In the classic water turbine all the guide vanes are positioned by a regulating ring which is rotated over a small angle by two large servomotors/cylinders if you like/each guide vane is connected by link to this ring. For emergency shutdown the main distributing valve which controls the main servomotors, is forced to the -close- postion by a separate device independent of the governor. This can be completely mechanical-hydraulic, and  can operate even if all the electrics are disabled.

We are talking of an oil supply available, usually 40 bar, for this the large pressure tanks which are seen on the photos, at generator level, are provided.

In the case of the Russian disaster, possibly the governor system on unit 2 went awry, and the guide vane positions became unstable, resulting in loss of control and the oft reported vibrations.

We can say that at the time of the flood, all the control, governor, and protection cubicles were carried away which meant that all the other operating units had no governors anymore and went to runaway.

In other words the guide vanes did not close, but remained in an uncertain partly open position.

The assumption is that all the other units were upgraded with the new controls.

The flood reached far out into the yard next to the control building, it must have been meters deep at generator level. One can see many overturned and swept away cubicles.

That is a possible speculative scenario.

regards, rasevskii


  

RE: Disastrous trafo failure in Russia

(OP)
yup. The next shiny thing in the 'puter controlling these big behemoths is "The turbine guide vanes/aka wicket gates/are positioned by individual oil servomotors which are evidently controlled by a digital system". This was to "improve" the efficiency of the turbine or something like that. And I said nuts to that when I heard it first time around. I asked exactly the same question, what if the damn servo motor fails ?

I am finding more & more younger crop sitting in front of ther laptops controlling these machines without even understanding how they work.

/rant over.

RE: Disastrous trafo failure in Russia

I agree edison123.

This is the case in all new plants. We only hear of the really big disasters. Most are never reported publicly.

In fact unit 2 just had a new governor installed. They had replaced the servomotor position feedback to the old governor, a mechanical cable/common practice/to save maintenance costs....

Many operators of existing hydro plants must be sleeping badly these days.

regards, rasevskii

RE: Disastrous trafo failure in Russia

On page 325 of the Russian blog is an item /post 6494/which
is an answer to someone querying the controlled positioning of the guide vanes, indicating that not all of the vanes were being correctly controlled from the governor signal. Upon failure of /electrical/supply, uncontrolled and mismatched closure is mentioned. That could be the cause of the reported vibrations in the water column or on mechanical parts.

In the photos of the destroyed turbine partly in the water, The guide vane individual servomotors can be plainly seen. The guide vanes themselves have broken off and disappeared.

See the photos on the most recent pages of the blog.

regards, rasevskii

RE: Disastrous trafo failure in Russia

(OP)
There are allegations of mind-boggling corruption in that Russian blog about that company, rushydro. It's odd that such a big disaster has not attracted more coverage from the western media.

RE: Disastrous trafo failure in Russia

On page 336 of the Russian blog one can find diagrams of the generator, turbine, and also the servomotor control linkages. The turbine dwg shows conventional control via regulating ring and links to the guide vanes. It can be the machine was never built this way. Possibly had individual servomotors from the beginning.

Question for Wolf 39- did the stator have direct water cooled windings from the beginning or was that a later rebuild?

regards, rasevskii

RE: Disastrous trafo failure in Russia


The generator stator windings were direct water cooled from the very beginning.

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM

RE: Disastrous trafo failure in Russia

Power factor tests on bushings will normally indicate problems which megger tests do not detect. It is a pain but worth it if you have to get inside the transformer.  

RE: Disastrous trafo failure in Russia


The "forums.drom.ru" thread was opened on August 17, just after the accident occured. Today, 360 pages and almost 7200 posts later, there is still speculation on as to what caused this tragedy. Was there an entire power plant separation from the grid first or was it just unit 2 alone that was disconnected and sped up? If only unit 2 was involved first, were the other units, especially units 7 and 9, destroyed by the water entering their pits? Or were they subjected to overspeed as well? Was a transformer fault causing all this and why did no. 2 rotor not perform as designed?

I at first tried to read all posts translated from Russian into English. The translations are most difficult to read and understand and I therefore gave up. Who can say that he (or she) has read every single post, digested them and made intelligent conclusions? I for myself will wait for an official report but I assume that even then there will be more questions than answers. Remember the John F. Kennedy assassination, the 911 drama and, lately, the Air France flight AF 447.

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM

RE: Disastrous trafo failure in Russia

Yes, I agree, Wolf. Strange words appear that have nothing to do with power plants. Such as:

knitting needles= spokes of rotor
ravines=sequences
wear and tear=operation
/to name a few.

Speculative scenario:

Reportedly, as they were trying to take unit 2 off line on Monday morning, it was not possible to reduce the load, as they approached the cavitation region, large low frequency vibrations and heavy pulsations occurred. Likely this was due to the new guide vane positioning system going unstable, and no longer following the command signal from the governor. It was said the parameters of the positioning system were set such that the gv positions began to oscillate.

The oscillation built up as they were resonant with the construction of the unit and the water column.

After many attempts to get the unit unloaded, the bolts holding the turbine top cover to the spiral casing/called the stay ring, I think,/ failed, resulting in the entire turbine, cone, and rotor being ejected vertically.

This can be seen on the recent pages of the blog, with diagrams.

As the turbine ejected vertically, all the guide vanes broke away., leaving a clear water passage...

The resulting flood wiped out all the station AC and DC supplies, protection and control cubicles throughout the station were destroyed. The remaining units became disconnected from the system due 500 kV protections operating in the remote switchyard. This must have happened over several minutes. All the electronic governors failed.

As there was no longer any power supply in the station, all panels having been destroyed, the other units went to runaway speed and stayed there until eventually the intake gates in the dam were closed manually using the crane there, which was running on its own built-in Diesel generator.

All the backup systems and protections failed, no power supply.

That is my take on it. We await the next chapters...

Can anyone explain how the two transformers blew up...?

regards, rasevskii
 

RE: Disastrous trafo failure in Russia


rasevskii:

You wrapped it up nicely and with the information available the scenario you described may be pretty close to the actual events. Lets wait and see for more details.

The single blade guide vane actuators installed at this plant are not a new invention at all. I remember a large unit commissioned more than 30 years ago where this system was introduced and worked nicely. And I'm pretty sure that more are in service somewhere else. However, if a shear pin fails and one guide vane goes astray, the resulting vibration is immense.

The public expects hydropower plants to work properly for 50 years and more without serious accidents. And there are  in fact quite a few power plants in flawless operation worldwide for even up to 100 years already. A prerequisite for such a reliable operation is of course a proper service and maintenance program.

The manual installation of all ten intake gates prevented further complications. However, intake gates are provisional devices only. For long term penstock sealing sets of stop logs have to be installed. For a multiple unit power plant usually only two or three sets are available for penstock and turbine servicing. Stop logs are also required for the downstream portion of the turbines to seal the turbines from the tailwater side. For servicing turbine impellers and other turbine components, the penstock and the tailwater side of the turbine has to be completely emptyed.  

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM  

RE: Disastrous trafo failure in Russia

(OP)
rasevskii

You trying to scare the beejus out of people ? :)

Agoram Muthukumaran
www.edison.co.in

RE: Disastrous trafo failure in Russia

rasevskii

Your synopsis certainly fits what we can see.  I am shocked that the turbine controls are not fail safe.  Every hydro governor I have worked on, as soon as the control power AC or DC failed the gates close.  The timming of the gate closure rate was fixed by limiting the movement of the distributing valve or needle valves on the servos (for small turbines) which keeps the pressure and speed rise to within acceptable limits.

This is an unusual configuration to have a servo per gate but as wolf says it can work nicely.  If you break a shear pin on a conventional servo/swing ring/gate set up you will still get a gate vibrating in the flow but that is why you have shear pin failure detection which a) shuts the gates THEN opens the CB AND drops the head gate.

Which brings me on to the next thing that shocks me, which is that the head gates had to be lowered using the crane.  On all the hydros I've been on the head gates drop all the way automatically under gravity and the hydraulic lifting ram limits the rate of fall so they don't hit the seal too hard.  We regularly tested this function under full flow too, good fun that job.

Given some of the comments about the state of the concrete in this dam, I'm concerned about how long the spill way will last given that it will be in continuous operation for the next few years.  Glade I don't live down stream of it.

Like most accidents the questions just pile up.

Cheers Niallnz

RE: Disastrous trafo failure in Russia

I saw a ppt floating in internet originating from a turbine consulting engineer.According to him capacity is 650 MWx10 units( Rushohydrosite also says capacity of station 6400MW) 16 blade Francic turbine ,142 rpm,commissioned in 1978.
Cause of failure-Sudden closure of unit 2 wicket gates due to an external object( log,stay vane,broken wicket gate etc)entering in turbine runner aand stuck in it as it could not pass the exit of the blades due to its size.Piece turned with runner and hit all wicket gates causing their sudden closure with in a fraction of second.Heavy water hammer and explosion of spiral casing.Another scenario presented is rupture of governor oil pipe in the closing side of distributed servomotors.

How  each generator is connected to transformer? Through generator circuit breaker? If not there is chance of overvoltage and overfluxing causing damage to transformer from sudden load throw off.

RE: Disastrous trafo failure in Russia

Hi Niall,

I'm guessing from your handle that you're a fellow Kiwi.  A number of the hydro sites that I have worked at, which were generally very typical of ECNZ/NZED/(etc..) sites in the North Island, were not set up to trip upon loss of control power.  They were generally mechanical governors, and would maintain present setpoint to avoid motoring the generators with the circuit breakers unable to be opened, and would need to be shut via handwheel control.  Wicket gates would default to something near "speed-no-load" if hydraulic pressure was lost.

Excitation was also operated on a similar principle to avoid loss of excitation events.

The installation of digital controls is obviously changing this to something more akin to what you are describe.

I agree with your other points though, especially regarding the headgates - these should be dropped based on a "station flooded" trip signal in the event of a major event as described.

RE: Disastrous trafo failure in Russia

Judging by the 1-line posted by slavag, each generator has it's own transformer winding and a circuit breaker is connected between each generator and transformer.

It's quite possible there was overvoltage when the controls were lost, but the generators are probably not capable of producing voltage greatly in excess of their rating.

I don't see anything in this video that looks like a catastrophic transformer failure. Has anyone seen better photos of the trannys?

http://www.youtube.com/watch?v=mmOOZJ7mdqY&feature=PlayList&p=BBC9DDB8D1BCF99F&index=3

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

RE: Disastrous trafo failure in Russia


Hi Alan:

There is a video in the net with a duration of 1:08 minutes. Left of the "fountain" one can see a cloud of black smoke. I know this is hardly visible here but I remember having seen an early video taken behind the powerhouse, next to the dam structure where this cloud emerging from a transformer was clearly noticible. Unfortunately I'm unable to trace this clip again.

Nevertheless: One should not blame one of the transformers for being responsible for the accident before having more information. The transformer bank with some bushings missing may have been damaged by falling debris, i.e. right after the powerhouse roof collapsed.

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM  

RE: Disastrous trafo failure in Russia

In the Russian blog, on page 406, is a posting by ++nonedub++ with diagrams of the gv control mechanism. In the text above it says:

/pasted in here/:

Cable connects the control levers of the blocks of regulating all servodrives (encircled by green color in the figures). In the block of regulation the valve, which governs oil feed into the hydraulic cylinder of servomechanism, is located. This cable ensures the synchronization of the individual hydraulic drives of blades TO the turbines. Foreshortening placed the new blocks of the regulations, which do not have mechanical synchronization. The synchronization of hydraulic drives became now purely program, type sensor - > processor - > the block of regulation for the servodrive of each blade.

/end of paste/

This pretty much tells it all:

Foreshortening=costcutting.

The electronic feedback system/maybe a digital system using an internet protocol or similar/went wrong or was set with bad parameters, the result: guide vanes at unstable/oscillating/huge discordances between individual gv positions/...

Result: huge pulsations/vibrations/ sideways forces of tons onto the turbine runner, destruction of the labyrinth seals, then the turbine guide bearing/ swinging of the entire rotating mass/contact between the generator rotor and stator, the normal air gap was 30mm....

At this point a number of protections had to operate, taking the unit off line, next: overspeed/gv are still out of control/...The station had not yet flooded, electrics were intact elsewhere.

We know the rest already, the unit destroyed itself, came the flood, the rest is known.

A possible speculative scenario.

Some hydro station owners/operators should not be sleeping well these days.

regards, rasevskii

 

RE: Disastrous trafo failure in Russia

Resevskii

I'm not sure that the translation to 'foreshortening' should be read as cost cutting, I think it could be read as upgrade or refurbish or some thing else that indicates they were installing upgrading to a new electronic governor.

The cable synchronisation system, as far as I can tell from looking at the diagram, I think works so that all the servos are a slave to one master servo.  One would have to assume that the master would also set the slew rate.  This system has the advantage not requiring a large (expensive) distributing valve controlling the hydraulic oil to two large servos as in a conventional system.  But the disadvantage is that there will be differences in the opening distange of each gate which could lead to vibration.

The risk with going to individual control of the servos is that the programmers may a convinced the station that the slew rate could be controlled electronically on the slave servos.  it would be a cost saving to not have to modify the existing control valves to the servos to have a mechanical limit to the rate that oil could be ported in/out of the servo.

I don't think that owners/opperators of other stations will be sleeping that badly. Stations of comparable size in the USA, Canada, Brasil etc have a different attitude and culture to safety.

Cheers niallnz

RE: Disastrous trafo failure in Russia

Quote:

It's odd that such a big disaster has not attracted more coverage from the western media.
It's true.  I didn't hear a peep about this on CNN.  But at least the important things like President Obama's snack habits and Jon and Kate's breakup are well covered!

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Disastrous trafo failure in Russia

"Stations of comparable size in the USA, Canada, Brasil etc have a different attitude and culture to safety."

Over here there is the belief at senior level that reams of paper risk assessments and method statements will somehow provide protection. Protection from litigation perhaps. The real key to safety isn't paperwork, it is carefully designed and engineered plant to eliminate or minimise risks so far as possible, and experienced well-trained staff who understand the hazards and how to work safely with them who make the difference.

While I agree that at a governmental and corporate level there are some big differences in attitude between Russia and some Western nations, I've found that many of the Eastern Bloc engineers are better educated and better trained that their western equivalents. Western power plants of recent years are built down to a price, not up to a standard, and while maintenance outage intervals are being extended the overhaul work carried out is being pared to the absolute minimum, something we have the beancounters to thank for. Our plants and staff aren't so much better built, better maintained, or better staffed that we can afford to assume that the Russian accident couldn't happen here.
  

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

RE: Disastrous trafo failure in Russia

(OP)

Quote:

plants of recent years are built down to a price, not up to a standard, and while maintenance outage intervals are being extended the overhaul work carried out is being pared to the absolute minimum, something we have the beancounters to thank for.

Well said, Scotty. One must learn from such disasters instead of being complacently dismissive about them. That's why I am frustrated by the complete news black-out of this terrible accident with loss of precious lives. Pete nailed it with the media's obsession with ridiculous persons and events.

Muthu
www.edison.co.in

RE: Disastrous trafo failure in Russia

For niallnz:

Yes I agree that the translation to costcutting must mean instead upgrade, refurbish, or modernization. Or something similar.

Looking at the gv control diagram, it appears that the gv are controlled in groups of three by one master servo. I think that there are 30 gv therefore 10 groups. The master servo for each group is likely an intelligent linear actuator, itself controlled by a digital protocol.

I have researched out the likely supplier of this system and downloaded some info. We cannot publish that here of course. It is the type of system widely used in machine tool controls and other industrial applications.

Agreed that likely the regulating parameters, opening and closing speeds, etc, are protocol controlled. A VERY dangerous method. The gv slew speed should be limited by hydraulic means only.

What is incredible is that there was -?- no sort of overriding safety system, no purely hydraulic-mechanical overspeed device, etc, that would shut the gv directly even if all the electronics had failed.

Also the intake gate should have dropped upon ESD condition, apparently this was not operational or not foreseen.

The electronic system would have been likely located at generator top level, and supplied from the station DC via a UPS or similar, possibly with multiple backup supply.  However, no one was expecting the station to flood, and all electric supply to be lost.

But this would not be the first hydroplant to flood. I can think of one plant that flooded to the level of the crane rails, submerging 3 units. A few decades ago...

I agree with your view on the culture of safety, maybe there it was a culture of complacency...

regards, rasevskii

RE: Disastrous trafo failure in Russia

(OP)
Thanks Slavag for that link.

It's a terrible accident. The main culprit seems to have been just one machine but with incredible collateral damages.

The missing carne rail mystery is solved for me. One end of the crane beam is supported on a gantry, which travels on the walkway. Never seen anything like it before.

Poignant comment from one of the survivors:

And now he can not stand the sound of water flowing from the tap.
 

Muthu
www.edison.co.in

RE: Disastrous trafo failure in Russia

2
I received this from a coworker today, didn't see it referenced in anyone's posts so thought I would share.  I apologize if it is covered by one of the links people posted, as I have not had a chance to browse them yet.

Attached is a PowerPoint file (in the zip archive) that contains annotated photos and theories as to what caused the accident.
 

RE: Disastrous trafo failure in Russia

Matt--

Thanks for the file.

old field guy

RE: Disastrous trafo failure in Russia


The discussion now seems to concentrate on the studs holding down the turbine cover. Quite a few failed by breaking. The fine thread of other studs propable were out of tolerance or simply rusted away. With about 20 bars present at rated head, and even more under the circumstances present when unit 2 failed, the nuts may have popped away thus giving way for the flood water. See for post 9654 of

http://forums.drom.ru/hakasiya/t1151239745-p483.html

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM

RE: Disastrous trafo failure in Russia

(OP)
Scary stuff, wolf. Hope the "authorities" involved in this mess are smart enough.

Muthu
www.edison.co.in

RE: Disastrous trafo failure in Russia

Either the second or third link in Wolf's post triggered my anti-virus - something called bloodhound.exe. Probably not a great thing to have on your computer. wink
  

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

RE: Disastrous trafo failure in Russia


Hi Scotty:

Sorry to hear that you are having problems with your anti-virus protection. My internet security software is being  constantly updated when on-line and I had no problems with the links mentioned. Today a complete virus scan after update didn't show any irregularity on my computer.

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM

RE: Disastrous trafo failure in Russia

Hi Wolf,

It was at work and corporate IT use Norton which ain't my favourite AV software. Hopefully it's a false alarm. I probably will have to answer some interesting questions about trawling a Russian internet forum, ha-ha. smile
  

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

RE: Disastrous trafo failure in Russia

For information (probably mostly for Russian-speaking colleagues) here is the official report of investigation authority about the failure on Sayano-Shushenskaya HPP .
http://www.gosnadzor.ru/news/aktSSG___bak.doc

There is a difference from Soviet era - information is public and several officials are pointed out as guilty.

------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant
 

RE: Disastrous trafo failure in Russia

For information too.
For Russian-speaking or used translators,
I would recommend: be carefull with this report.
Lot of technical guys are not agree with this report.
Please see:
http://www.fedpress.ru/federal/econom/tek/id_156975.html
 Best Regards.
Slava

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