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 ?

 

[edison123]

Oil filled trafos are silent beasts.

 

[oldfieldguy]

"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

 

[edison123]

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

 

[oldfieldguy]

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

 

[waross]

Thanks for the inside info Old Field Guy. LPS

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

 

[edison123]

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

 

[oldfieldguy]

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

 

[ScottyUK]

"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!

 

[waross]

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

 

[hilotech]

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

 

[prc]

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.

 

[edison123]

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.

 

[alehman]

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

 

[oldfieldguy]

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

 

[wolf39]

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

http://WWW.HYDROPOWER-CONSULT.COM

 

[dga1960]

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

 

[alehman]

A video clip from the incident in progress.

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

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

 

[wolf39]

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

http://WWW.HYDROPOWER-CONSULT.COM

 

[itsmoked]

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