A couple of years since the accident at the Sayano–Shushenskaya Dam, but quite an informative video which i hadn't seen before.

http://www.youtube.com/watch?v=XJ6G0rxnzbw
  

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

A star for you Scotty.  Thanks for posting this.  It is a good follow up to the photos we saw when this initially happened.

Tragic, and worse, avoidable.  Doubly tragic.

rmw

Itially there waas some concern of sabotage,  

What was the documented reason for the failure?  I never heard.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

High machine vibration leading to failure of the bolts or studs holding the turbine together. The whole 1800T assembly was launched, still rotating, vertically upward by the force of the water. The vibration problems were exacerbated by the machine operating in a part-load region where it was not capable of sustained operation. At least, that's my two-line summary. The hydro guys can explain it better.
  

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

Hello everybody:

msquared48 and all, here you can get a complete (in my opinion) technical explanation about that accident.
http://www.waterpowermagazine.com/story.asp?storyCode=2058518

So the author is postulating a variation on pressures due to water hammer from too rapid a vane closure to the system, the turbine assembly being the weak link that failed?

I thought these emergency shutdowns were computer controlled so something like this would not happen.  Seems like the wickets would fail before the turbine was thrown up and out.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

Thank you. That's a decent article - they have been quite scarce for such a major incident.
  

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

Hydro units of this vintage are generally controlled by a mechanical governor.  In our plants the maximum wicket gate speed is ultimately limited by the hydraulic oil flow rate through the main spool valve.  But if a hydraulic line between the servos and the governor were to fail then gate closure would be uncontrolled.  Water hammer would over pressurize the penstock and the draft tube water column would separate.  Our hydro units have surge tanks and pressure relief valves to avoid the former and vacuum breakers to avoid the latter.

The other possible cause of rapid wicket gate closure is if trash, such as a small log, gets past the trash rack.  A long slender item could get caught in one of the turbine passages.  As it rotates around with the turbine, the object could strike each wicket gate with enough force to break the shear pins.  Depending on where the wicket gates are balanced (center of pressure relative to the axis of rotation) they could slam shut.  To avoid this, we regularly inspect our trash racks.

Tom Moritz
Mechanical Engineer
US Bureau of Reclamation