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Help save the last mercury arc rectifier substation
Posted by mikeselectricstuff on 03 Aug, 2013 16:52 -
https://www.facebook.com/SaveOurSubstation
If you don't know what a mercury arc rectifier is, check out my page: http://www.electricstuff.co.uk/mercarc.html
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Do you know what happens, if one of those break while in service?
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Superpowers for those within 50m?
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Heavy metal intoxycation, police, court, 300.000+$ out of your pocket, lawyer, court again, prison for a few year
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Do you know what happens, if one of those break while in service?
?
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in action
It's a shame not to save such a historic station. -
That stuff is practically steampunk. It should get listed for preservation as a historical monument. Do people not realize how wonderful it is?
It's a sad thing that historic technology is always struggling to be preserved, and it always falls to the general public to do it. -
That stuff is practically steampunk. It should get listed for preservation as a historical monument. Do people not realize how wonderful it is?
It's a sad thing that historic technology is always struggling to be preserved, and it always falls to the general public to do it.
Do you know what happens, when a wonderful, hot, operational, energized, multi-phase, multi-KW Mercury vapor rectifier, a historical piece of technology, breaks?
Mike can do whatever he pleases, as far as I am concerned. I just wish to ensure he knows what he is up against. He is advertizing for these on his homepage, and apparently somebody in the UK is planning on putting one of these in a public museum. Operational, that is.
Just for the record: I don't really believe in the Nanny state, nor in putting warning stickers on everything. Because they dilute the actual warning signs. Those, which you really, really shouldn't ignore. As a result these days it is hard to have a cordial exchange involving potential safety issues due to all the muppet replies you will attract.
ProTip: MV rectifiers were dumped as a technology at the earliest convenient moment by most of the world, as soon as semiconductors were a viable alternative for the various power levels. They weren't dumped due to looking dull, or because they didn't work or were unreliable.
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Mmh if this thing break, mercury vapor will arch and short and maybe became plasma... Funky!
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Do you know what happens, when a wonderful, hot, operational, energized, multi-phase, multi-KW Mercury vapor rectifier, a historical piece of technology, breaks?
No. But I'm now curious. Please tell. -
ProTip: MV rectifiers were dumped as a technology at the earliest convenient moment by most of the world, as soon as semiconductors were a viable alternative for the various power levels. They weren't dumped due to looking dull, or because they didn't work or were unreliable.
They could place it in a secured chamber as museums do with old artefacts :-) -
That stuff is practically steampunk. It should get listed for preservation as a historical monument. Do people not realize how wonderful it is?
It's a sad thing that historic technology is always struggling to be preserved, and it always falls to the general public to do it.
Do you know what happens, when a wonderful, hot, operational, energized, multi-phase, multi-KW Mercury vapor rectifier, a historical piece of technology, breaks?
Mike can do whatever he pleases, as far as I am concerned. I just wish to ensure he knows what he is up against. He is advertizing for these on his homepage, and apparently somebody in the UK is planning on putting one of these in a public museum. Operational, that is.
Just for the record: I don't really believe in the Nanny state, nor in putting warning stickers on everything. Because they dilute the actual warning signs. Those, which you really, really shouldn't ignore. As a result these days it is hard to have a cordial exchange involving potential safety issues due to all the muppet replies you will attract.
ProTip: MV rectifiers were dumped as a technology at the earliest convenient moment by most of the world, as soon as semiconductors were a viable alternative for the various power levels. They weren't dumped due to looking dull, or because they didn't work or were unreliable.
Kew Bridge Steam Museum is planning on having one of these on display.
It's normally far more productive to say what you mean rather than ask silly questions and say why they weren't dumped.
So what happens? -
Only reason they were discontinues is because the replacement units required less cooling, and were essentially maintenance free and could be operated in any orientation. The mercury pool needs periodic adjustment and cleaning of the glass outer envelope, and needs a lot of cooling. Thus the lower losses and reduced control gear requirement of the solid state rectifiers ( no keep alive exciter and associated resistors and transformers) made them attractive for upgrades that still used the same transformers ( most expensive part of the station) and which occupied a smaller footprint in the plant floor allowing either another feeder bank or extra output circuits to be connected in the freed up area. As well the lower losses made a smaller fan usable, and as well smaller cheaper and longer lasting filters and less frequent filter cleaning, a savings on cost of maintenance. Mercury arc recifiers have a closer tolerance of operating temperature than silicon diodes, which can run happily at sub zero temperatures and survive thermal shock much better than a large glass bowl.
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There are plenty of details on the wikipedia entry. But basically, these have a fair amount of liquid mercury in them, stored in a brittle glass bulb. If they shatter then the result is a very nasty environmental hazard / cleanup expense. And I suppose in an explosive shatter there is probably quite a bit of vapor ejected too. Think about how freaked out people get over a single cracked mercury thermometer or tilt switch, and multiply that by a million.
Also, the larger ones (steel, not glass) required constant pumping to maintain sufficient vacuum. This essentially means that they were constantly emitting mercury vapors into the environment.
Lastly, the beautiful purple glow they emit while operating is very heavy in a wide range of UV wavelengths. I'm not sure I would want to stare at one or even stand near it for too long. -
FWIW, the old Glebe Island swing bridge in Sydney, has a big mercury arc rectifier onsite, that was used to provide the DC for the motors that swung the bridge.
It's in a small shed at the Eastern end of the bridge approaches. Or at least it used to be, um... around 2001 or 2 when I saw it. At that time the cabinet it was in was still powered up, so I suppose it was still operational.
Unfortunately, I don't have photos. -
There used to be one in the science museum in London, as I remember it was under the stairs and was used to power the lift, at certain times of the day it was opened to public viewing as well, I would expect that if you watched it too long you would get a good tan.
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There used to be one in the science museum in London,
Any idea what date that was? I thought I'd seen a couple in the Science museum, one working, the other just for display. This would have been around 1970. -
It's normally far more productive to say what you mean rather than ask silly questions and say why they weren't dumped.
In general I'd agree with that, and I had my doubts about how to approach this. In Mike's case in particular I found it would feel pretentious to give a long and potentially unwanted explanation out of the blue. I would much prefer if he had just said he was on top of things.(...)
As far as I can tell, then all of this is accurate. That is however not what I was getting at with the 'dump' comment. I am not old enough to have worked with MV rectifiers, back when they were widely used, but my mentors certainly are. According to them many industrial MV installations were actively decommissioned ASAP, as alternatives became available. This makes it even more amazing that some are still in active service.There are plenty of details on the wikipedia entry. But basically, these have a fair amount of liquid mercury in them, stored in a brittle glass bulb. If they shatter then the result is a very nasty environmental hazard / cleanup expense. And I suppose in an explosive shatter there is probably quite a bit of vapor ejected too. Think about how freaked out people get over a single cracked mercury thermometer or tilt switch, and multiply that by a million.
Oh, but it is much better than that.
OK, here is the (overly long) explanation: Why you (probably) don't want an active MV arc rectifier in your home or museum.
The background here is that metallic Mercury at room temperature is pretty benign. It wouldn't be a good idea to ingest some, but having it sitting in for instance an open bowl would not be a major problem. The reason is that the vapor pressure of Mercury at normal room temperature and air pressure is quite low, so the rate of evaporation would be negligible. Even accidentally dropping some Mercury on the floor of your lab isn't that much of a problem. There are even standard lab tools for dealing with this situation, so you are probably fine if you pick it up in a reasonable time frame. The rate of evaporation will be miniscule due to the relatively small surface area exposed to the air.
Enter the industrial, glass encased MV arc rectifier, and its smaller sibling, the 'vacuum tube' edition with a heated cathode.
The first problem is that to make a decent live display of a large MV arc rectifier, you need to pass some *serious* power through them, along with the cooling to match. There is a video on YouTube showing Mike's substation in action, and here it powers a train, or rather a tram. To put this in perspective, then a KW level radio transmitter would just need a single pair of beer bottle sized MV rectifiers for its PSU. So you need serious power/current for your live display (or show it in complete darkness, and hope people won't be too disappointed).
The second problem is that you need flexible leads for most of the electrical connections to the rectifier. Otherwise the mechanical stresses due to thermal expansion would cause cracks in or downright failure of the vacuum vessel.
So even if gravity helps out, then in case the glass vessel breaks there is a very good chance you'd - briefly - have very conductive Mercury, lots of electricity and wildly dangling wires all over the place. This is in addition to the Mercury dropping down on the cooling fan and being splattered all over the place. Those of you, who may have seen an accident involving a car battery, may be able to guess what comes next.
"Mercury smoke. Don't breathe this."
OK, so maybe we predicted what was about to happen, and teleported out of there just before the Mercury hit the fan. We'll just wait for the Mercury to condense out of the air and go clean up. Right?
Erm, no, this is where it gets ugly.
We just created a sizable amount of microscopic pellets of liquid Mercury, small enough to be carried short distances by the normal air currents. Genuine Mercury smoke. That stuff will go everywhere in the building in question, snuggling into every nook and crevice in fabric, untreated wood, clay/brick, etc. Even better, the tiny droplets will create an amalgamate with many metallic surfaces, making the Mercury impossible to clean off.
And for fun, the total surface area of the combined mass of micro droplets is no longer trivial, compared to the vapor pressure. Additionally the Mercury will also stick to hot surfaces, like stove plates, room heaters, incandescent light bulbs, electronics and more. As a result you now have noticeable amounts of Mercury vapor in the local atmosphere, at least until you remove all the Mercury smoke particles from, well, every surface in the building. Which is physically impossible.
You now have two options:
*) Clean away any visible traces and spills from the accident, and pretend it didn't happen. This is likely to cause children spending much time in the building to grow up and be stupid. Literally. Adults are just likely to get sick, and may potentially die in due time. Mercury is like Lead, just a lot worse.
*) Condemn the building, tear it down, and store its remains and the items within as hazardous waste. This will be a popular option for a museum.Lastly, the beautiful purple glow they emit while operating is very heavy in a wide range of UV wavelengths. I'm not sure I would want to stare at one or even stand near it for too long.
Shhh! Some people may use this as a selling point, as the museum visitors may actually want a nice tan...
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..or you just put it in a clear perspex case, with a tray big enough to catch everything, probably with some sand to reduce splashing. You can avoid the fan issue by running at low power and/or intermittently.
..and of course avoid breaking the glass in the first place...
Siemens Museum in Munich has a MAR on display btw.
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The second problem is that you need flexible leads for most of the electrical connections to the rectifier. Otherwise the mechanical stresses due to thermal expansion would cause cracks in or downright failure of the vacuum vessel.
Is this really a problem? I think you are seriously underestimating the competence and expertise of the people* that are dealing with these devices. You live in a very scary world - I'd better not trouble you with the experiment that we were asked to perform as part of the school chemistry (reduction of mercuric oxide, ... with a Bunsen burner and blow pipe).
*Actually, considering the multitude of pratts on youtube, you may have a point. -
Mercury's not that bad, I used to crack open tilt switches as a kid and play with the stuff in my hands. Never did me any h 3g 874t 394ty 9ghghrifdf hdifg heruighierh giaeuger'[ergberiuvbiaf erubvhv[b avuig ivi
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On a work experience school excursion we visited our local technical college in Wollongong and they had one of these in their lab (early 80's). It sat in a big enclosure with Perspex viewing windows. They didn't energise it for us but I asked what it was and when they said it was a diode we all broke out laughing. I wonder if they kept it
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The Fun Museum at Cowra (NSW) has three mercury arc rectifiers. One of them is set up with the transformers for demonstration. There was no one there when I was there so I turned in on and had a play with it!
It's a very interesting place that has so much historical stuff in there. It is apparently a private collector's personal museum open to the general public. -
FWIW, I think it's now illegal for any school in the USA below college level to have any mercury whatsoever in their possession. Doesn't matter if its a chem lab or anything else. No mercury. IMO, the stuff isn't that bad if handled intelligently, but hot electrified mercury? No thanks.
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FWIW, I think it's now illegal for any school in the USA below college level to _______________
You could probably fill in the blank with anything that anybody has ever been scared of.