Homeowner shuts down U.S. nuclear plant for 3 days — Tree fell onto transmission line after being

Homeowner shuts down U.S. nuclear plant for 3 days — Tree fell onto transmission line after being cut down

enenews.com

[...] an interruption [was] caused by a large tree falling onto a transmission line.

Tennessee Valley Authority spokeswoman Gail Rymer says automatic shutdown procedures began at the Watts Bar plant when the electrical fault was detected on Friday afternoon.

Rymer says a homeowner cut down the tree that fell onto a 500 kilovolt transmission line close to the plant [...]

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At first I wondered just how weird this sounded and whether it could be true but there is a video report about it. It seems incredible that it would be shut down for 3 days.

Those of you with knowledge about the size of the line, and how this could happen, please inform me. I am picturing transmission lines running from pylon to pylon and they are huge and usually too high for any tree to reach.

enenews.com
(visit the link for the full news article)

reply to post by aboutface


Nuclear power plants are not allowed to run on there own energy. It is a safety measure put in place to keep a power plant from being a run away bomb I guess. So the guy probably is on the same power grid the plant runs on. The three days would be having to go through a long shut down process a check of systems then a restart process.

reply to post by JBA2848


Thank you for your reply. I forgot about the shutdown and start up time, but that makes sense.

However I am still not clear about transmission lines versus ordinary power lines. Aren't transmission lines the main distribution lines?

The ordinary lines you see outside your house/around town etc are three phase 120VAC (Volts AC) lines. To put it simply, what your house runs on. The particular transmission line that got knocked down was 500 kilo 500*(10^3)V DC. These transmission lines go to substations where they are converted back into useable grid ac power.

So yes, a 500kv line is the line that distributes the power to different substations around the particular area. With the line taken down, the plant has no way to transmit its energy through the lines, so they had to shut it down.

That must've been a hell of a tree because those lines are usually 80+ feet above ground.

reply to post by spolcyc88


Exactly my problem with the story. I'm still having trouble understanding how this could happen if it was a transmission line.

I have a hard time believing that they didn't clear any potential hazards while constructing the line. The only other thing I could think of would be the fact that when the lines heat up (on a hot day etc) they can sag quite a bit and when the guy "cut the tree down" the line happened to be low enough to hit it. If that is the case, then there was a severe lack of foresight when putting the line up not to clear obstructions near it.

reply to post by aboutface

I kind of doubt that a tree shorted out a 500 KV lead. What is more likely is an increasing cascade of overloads back travelled up the line. If the ground fault detectors registered a load and tripped in a neighborhood from a tree branch that could happen under the right circumstances (I guess).

A half million volts would destroy just about anything you touched it with. Thats why they are so high off the ground.

reply to post by intrptr


I watched transformers blow during the '98 ice storm. If cascading failures backed down the line, what would normally happen to the transformers?

reply to post by aboutface

Transformers step up or down voltage. In a storm there is a heavy load on the line. Uninterrupted shorts put too heavy a load and the breakers can't trip because they are frozen I think. But a cascading short that causes a trip transfers its load to the next branch and so on each in turn functioning properly by tripping. But that buildup of current has to go somewhere so it is routed to another branch and then that blows too. Each time the load gets heavier and thats how power outages happen. Usually the short is hundreds if not thousands of miles away from the "source" so it is stopped by then.

If a power transformer is hit by one of these surges it can explode, yes. I am not a line man so I may have some of this wrong.

Remember the big blackout in New York? It started in a shoe box size relay on a telephone pole. I have heard of rats causing whole cities to go dark before. A lot of it depends on the weather, maintenance, and aging grid "theory".

reply to post by intrptr


Grid problems are usually carefully analyzed and studied. All this makes me feel that our nuclear power plants are way more vulnerable than I would have believed.

Originally posted by JBA2848
reply to post by aboutface

 

Nuclear power plants are not allowed to run on there own energy. It is a safety measure put in place to keep a power plant from being a run away bomb I guess. So the guy probably is on the same power grid the plant runs on. The three days would be having to go through a long shut down process a check of systems then a restart process.

edit on 3-7-2013 by JBA2848 because: (no reason given)

Only the navy runs nuclear power plants on there own energy.
Civilian nuclear power plants run a two power setting 100% or shut down on generators for cooling.

If they can not send power somewhere they scram. emergency shut downs cause them to have to bring the plant back slowly to make sure the scram did not damage anything. its testing all the time when a plant recovers from a scram.
A scram could cause hot spots in the fuel rods warping them.

The first reactor the Chicago Pile had control rods held up with rope and the term scram was Safety Control Rod Axe Man
If something went wrong there was a guy that would run up with a axe and cut the rope.

Also newer nuclear plants can have a loss of load without scram. Meaning they don't need to shut shut down if this sort of thing happens.


reply to post by spolcyc88


Sure it was DC and not AC?

Originally posted by aboutface
Exactly my problem with the story. I'm still having trouble understanding how this could happen if it was a transmission line.

It's a good question.

Look toward the end of this video, and you can see what appears to be some trees a little taller than the power lines:


Even if one of those trees fell on the line, it wouldn't damage the line, as those top branches are small and the line is very strong. However, while dry wood is a good insulator, the wood in trees isn't that dry and may form a semi-conductive path to ground.

So if the story really happened as reported, my guess would be that the falling tree brushed against the lines, allowing the power from the line to flow through the tree to ground, triggering the automatic protection circuitry, resulting in the shutdown.

The power companies usually spend a fair amount of money each year on tree trimming to keep growth away from power lines.

reply to post by C0bzz


Transmission is done in high voltage low current DC. At least here in the Pacific Northwest, in which most of our power generation is sent to California so the increased losses associated with long distance AC transmission are avoided.

Most trees aren't high enough to reach the lines.
And...
If you ever take a look at a high voltage transmission line going through the countryside, all the tall trees are cut back in a wide swath, eliminating the possibility that one could fall on the lines.

reply to post by spolcyc88


HVDV is typically used for long distance transmission, or between unsynchronised grids. AC can still be used for transmission and is more cost effective at shorter distances.

Also power engineering is awesome.

reply to post by aboutface

Grid problems are usually carefully analyzed and studied.

Americas grid is aging rapidly. There are a lot of related issues. Replacing the whole thing would break the power companies, so they usually resort to fixing what "breaks".

However the nuclear plants are just water boilers. They don't actually generate power, just steam. The building where the generators are is a wholly separate operation. If the generators tripped because of a failed transmission line that does not harm the nuclear power portion of the plant. Neither does it scram. Scram is a reaction to an emergency issue of loss of main power for cooling pumps or coolant flow. More like the plant is taken "off line." The core continues to operate but in standby mode.

Usually when the generators trip they need to check all related systems then slowly bring it back up to turns before going back on line.

They don't just throw a switch. Thats why the three days. If it had scrammed it would take weeks of testing and inspection.

reply to post by ANNED

The first reactor the Chicago Pile had control rods held up with rope and the term scram was Safety Control Rod Axe Man
If something went wrong there was a guy that would run up with a axe and cut the rope.

Never knew that before. Thanks for bringing it. I started a thread on a similar note here:

www.abovetopsecret.com...

The lonely and the brave.

reply to post by Arbitrageur


If there was more than one line, it's also possible that as it fell it pushed the outside line into one of the other ones.