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 ?

 

[rasevskii]

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

 

[jimbofitz]

News from the owners website:

http://www.eng.rushydro.ru/press/news/7673.html

 

[itsmoked]

Thanks jimbofitz.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rasevskii]

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

 

[edison123]

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.

 

[rasevskii]

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

 

[wolf39]

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

Regards

Wolf

http://WWW.HYDROPOWER-CONSULT.COM

 

[xxjohnh]

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.

 

[wolf39]

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

http://WWW.HYDROPOWER-CONSULT.COM

 

[rasevskii]

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

 

[wolf39]

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

http://WWW.HYDROPOWER-CONSULT.COM

 

[edison123]

rasevskii

You trying to scare the beejus out of people ?

Agoram Muthukumaran

http://www.edison.co.in

 

[niallnz]

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

 

[prc]

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.

 

[mgtrp]

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.

 

[alehman]

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

 

[wolf39]

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

http://WWW.HYDROPOWER-CONSULT.COM

 

[rasevskii]

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

 

[niallnz]

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

 

[electricpete]

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!

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