There's all kinds of stuff on the net if you just Google the story, or are you suggesting that these are not providing the details that you're looking for?

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

I've read about the incident, the public description and photos are eerily familiar. Our company, an electric utility, lost a 280 megawatt unit in the mid-1990s. The circumstances have a lot of parallels. Coincidence... maybe, maybe not.

The unit we lost was coal fired, same as St. Clair Station. The fire had nothing to do with the boiler or coal combustion.

Due to operator error, an off-line unit's generator was accidentally connected directly to the electrical grid. This caused the generator to respond as an electric motor and rapidly accelerate (along with it's steam turbine) toward synchronous speed (3600 rpm). (Perhaps the "letting go" you heard about.)

During the acceleration, mechanical damage occurred, throwing the turbine / generator out of balance. Vibration cause several big problems:
Ruptured a hydrogen cooling line which then exploded as a result of gross sparking in the generator. (An explosion was reported at St. Claire).
Vibration ruptured turbine lubricating oil lines, which ignited as a result of the hydrogen explosion. (Notice the black smoke coming from St. Claire).
Vibration pulled the machine's anchor bolts (about 4" diameter x 4' long) out of the reinforced concrete turbine / generator pedestal.

The combination of electrical shorts, hydrogen explosion, lube oil fire, and structural damage put the unit out of operation for well over a year. I handled the civil-structural rebuild along with reinstallation of the factory overhauled several hundred ton generator stator.

www.SlideRuleEra.net
www.VacuumTubeEra.net

Not all that far from there, back in 1966, there was another power plant accident, only in this case there was no smoke or fire. In fact, from the outside, it looked like nothing had happened at all. However, if the accident had not been addressed as quickly as it had been, we could have lost Detroit.

I'm talking about the Fermi I Nuclear Power Plant between Detroit and Monroe, MI. The incident was a partial core-meltdown and it was after this accident that the term 'The China Syndrome' was coined, referring to a scenario where a nuclear reactor core melted-down to the point where it breached the containment building, which did NOT happen in this case, but it was a close call. And to make matters worse, this was not your typical light-water reactor but rather a liquid-sodium cooled, fast-breeder reactor designed to produce Plutonium as a by-product while producing electricity for commercial use by a public utility.

One of my cousins worked there during the construction (he was an electrician) and a few months before they started to load fuel he arranged for our family to get a tour of the facility including a chance to walk inside the containment structure itself right up to where the core of the reactor was going to be. I was 15 years old at the time.

Here's some background info on this power plant with details of what happened and why:

http://news.blogs.cnn.com/2011/03/29/u-s-nuclear-p...

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

So why would an of-line unit have hydrogen in the unit? I thought most utilities, or at least the ones I've work with, do a nitrogen purge, then leave the unit open.

Quote (So why would an off-line unit have hydrogen in the unit?)

It was New Years Eve, I was not present but my understanding is the unit was off-line... but on standby, on turning gear. Ready to be brought on-line in a couple of hours, if needed.

In the investigation, employees who were present stated there was a hydrogen explosion. Damage to the turbine building structure was consistent with a hydrogen gas (lighter than air) explosion / fire. That is, heat damage to high roof structure, but minimal heat damage to the T-G pedestal and turbine building floor, except where burning lube oil flowed.

www.SlideRuleEra.net
www.VacuumTubeEra.net

Long ago, I had an opportunity to tour the coal-fired power plant up north of Fort Collins. That is one of the smaller coal-fired facilities, I understand. But I remember at some point, somebody made the statement that if they blew that turbine up, that would probably bankrupt the utility.

Insurance is a good idea.