Russian Hydro Accident - Armchair photo forensics

Submitted by Jeff Buster on Tue, 08/18/2009 - 11:31.

Take a look at the lower two images from BBC and help me understand how a transformer explosion could lead to the generator breaking loose from it's foundation and blowing a huge hole in what looks like one meter thick reinforced concrete?   It looks like the generator was rotating when it broke loose, because you can see the windings are all twisted in the same direction.  The left hand photo shows that the penstocks were ruptured, blasting water directly into the power gallery and washing debris out onto the roadway.  

Could this really be set off by a transformer explosion?   Are the transformers in the Generator Hall? Or outside? 

I have not had time to research the layout of equipment at Sayano, but often the turbine is below the generator floor.   Rather than a transformer explosion, which the BBC reported, it seems more likely to me that the turbine ran away and self destructed taking the penstock with it, or that the penstock ruptured - and an 800 foot tall column of speeding water entered the turbine room, ruptured the concrete floor upward sending the rotating many many ton generator spinning around wildly like a atomic top.

Who's got another quess?

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Armchair forensic engineering - Sayano dam accident

 

No newspaper or news feed (like AP or Reuters) can match what individuals can supply with the internet – and supply not because they are driven by money or advertizing, but because of their own passion in the issue –
Check out these videos of the Sayano-Shushenskaya hydro electric dam accident.   The videos make it clear that the primary cause of the physical damage was from tremendous hydraulic (speeding water) forces.   
 
This Voice of Russia news update rules out sabotage or transformer explosion (The BBC first reported that a transformer exploded – which I expressed skepticism about in the first post in this thread).   The VOR appears to suggest that the critical failure may have been in a penstock gate (valve).   Which caused the turbine to overspeed? And self destruct?  
 
Come on you armchair forensic engineers:   look at these videos and put your theory out there for the public to criticize!  Notice the concrete column which is opposite the generator which self destructed and bent all its windings - the column has been eroded by the force of water - without the penstock gate (or another gate at the top), the only way to shut off the water is to lower the dam level - that takes a bit of time. 
 
Let’s say the height of the water column in the penstock is 800 feet, and that the penstock pipe is 10 in diameter, and that the water is allowed to fall down through the penstock so that it is almost in free fall (to build up inertial energy to slam against the turbine rotor cups) – what is the amont of kinetic energy which a gate valve must be able to withstand as it shuts – what if the valve shuts too fast?   Wikipedia has a section describing various hydraulic turbines – was the Sayana plant and impulse turbine?
 
Stopping a train puts huge horizontal forces on a train track – and is usually the design weakness for trestles.  Stopping this weight of falling water is like stopping a freight train – falling straight down.  

 

Hydro Accident

Generators are located under the floor level shown in most of the photos and videos. The turbines would be located below the generators. The turbines are most likely "francis" type with a case like a flat snail shell.  The transformers(orange, three per generator?) are between the building and the Dam, just upstream of major damage.

Most likely a mistake or failure in the control system caused the first turbine and generator to "run-away." This could have been a short or overcurrent of the main transformer. Or overheating due to loss of coolent, etc.

There should have been a controlled shutdown of the turbine on loss of load by the safety equipment and turbine controls. If these controls operated late or failed, then the turbine speed increases to a maximum overspeed, and then if the water is stopped quickly, the result is a very large water hammer surge. this is like the banging of pipes in the house when the water flows fast and then is stopped suddenly. This would cause failure of the pipes or turbine case, and the associated flooding the damage to the other two units which were operating.

WOW!