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Computer wiring tunnel, abandoned coal power plant. Photo by Bryan Buckley. (lemmy.world)
submitted 9 months ago by to c/pics@lemmy.world
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[–] 24 points 9 months ago (19 children)

Why does a power plant need that much circuitry in the first place? I get that it's probably super-old and probably built back when you needed a whole server rack for the equivalent compute of a pocket calculator (and also it's relatively bulky because it's a lot of relays for switching high-current stuff), but still, a coal power plant shouldn't be that complicated, right?

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  • [–] 43 points 9 months ago (12 children)

    It's about IO not compute. The controllers for plants like this aren't very complicated but they can have many thousands of signals going to/from them. For a ~500MW plant I'd expect somewhere between 2-5k IO, more if it's nicely automated.

    Automation engineer, have worked on power plants.

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  • [–] 6 points 9 months ago (6 children)

    Who would win? An over-stuffed cable tray, or 4 twisty bois?

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  • [–] 8 points 9 months ago (4 children)

    What? The IO is digital inputs and outputs, analog inputs and outputs.

    Then there's power distribution and 24v DC device power (or 120v depending on application and often age), relays, contactors, timers, VFDs, etc. This is what the world runs on. Networking cables like that Ethernet are still part of it but a pretty small part. They just get plugged into all the PLC racks and any other device that needs it. Some of what I described can be replaced with automation and code, but only the very old legacy devices a lot of these old plants and mills still have around because they're still functional..

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  • [–] 1 point 9 months ago

    Yeah, exactly. You definitely save some copper by running ethernet to remote racks but by raw wire count it's not reduced much. There's a LOT of modern plants (power and manufacturing plants) that have way more wiring than this in a photo

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  • [–] 1 point 9 months ago (1 child)

    My point (if you can call it that) is that you can have remote racks and cut the total footage of wire by 75%

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  • [–] 0 points 9 months ago

    But then you have many racks that could fail, any one of which taking the system out. So you add redundancies and now you have a small "server room" in each section of the building that needs to be clean enough to inspect devices without getting sut or coal dust on them.

    Engineering is about tradeoffs.
    Sometimes that means sticking enough RAM in a missile that runes out of fuel first and sometimes you run a lot of cables, but make up for it in reliability and easier maintenance.

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  • [–] 2 points 9 months ago (3 children)

    Why so many? Is it a relatively small set of signals multiplied over multiple boilers or something, or is each line really doing something different, or what?

    Are modern plants similarly full of wires, or have they streamlined it (e.g. by multiplexing a bunch of signals as packet data on a single networking cable)?

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  • [–] 7 points 9 months ago* (1 child)

    Um, I mean the boiler(s) itself are a small part of it. It's all the other stuff. I am not a coal expert by any stretch, but if you think of the signals required just to convey coal, probably dozens or more of drives with run/stop/various errors/temperature/current/voltage/perhaps VF, plus all the sensors you need to use motors like that with (presumably bucket conveyors?) like slip, like explosion disk detection from dust. Not like all of those have to be present, but every step has so many signals.

    Plus then you've got a steam turbine and a switchyard, plus all the plant utilities like process heating and cooling water, compressed air, steam turbine makeup water, etc

    Nowadays you do IO to remote racks that are close to devices (like valves/motors/etc) then use Ethernet to make it go further. Pre ethernet there were typically proprietary cables for the same, but thankfully that's a thing of the past

    But something like I mentioned with a motor drive having all those signals, yeah it's typically just an Ethernet cable + power + estop (usually hardwired still). So maybe 40-50 wires down to 5-8

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  • [–] 4 points 9 months ago* (last edited 9 months ago)

    Whether its a power boiler or a recovery boiler there are a huge number of sensors and actuators needed to monitor and adjust. Just the pressure systems at the various points inside the boiler tubes. Required miles and miles of copper cable. There is also a huge number sensors and actuators in the fire box from the fuel feed to the exhaust and anti pollution systems.

    Then you move on to the turbine section and you have more wiring for that.

    I once saw the aftermath of a single oil sensor failing and not going to zero. It hung and didn't alarm. The the babbit bearings on the turbine side seized. The whole place nearly melted down until the engineer on site managed to get the boiler shutdown with very minimal damage to the boiler. They fired him the next day for the maintenance miss and they had to rebuild the whole turbine because the blades got wet.

    Power boilers if they lose water they will melt from the hanger to bottom. I've seen the aftermath of that as well. So the old legacy stuff is here to stay until it stops working.

    Nukes were that times ten. Multiple sensors for any given system plus stand by emergency systems all leading to control room. Inside the containment vessel there are cable trays everywhere on every level. The support equipment outside the containment vessel were no different. It is unlikely most of that will can ever be replaced. Many of these systems take a decade or more to slights retrofit because with a nuke you can't really make a mistake.

    I sat in on multiple meetings because a pump housing mounting bolts were supposed to be left handed threads but were right handed instead. It took them over a week to decide if it was okay that way. Engineering office guys were trying really hard to not to have to submit all the paperwork to get the prints changed after nearly twenty years in service. It would have been very costly in time and materials to remove the studs in the floor and replace and repour the floor section so they kept the right handed threads. This should give you some idea how hesitant they are to change anything in a nuke. I can only hope in the nearly thirty years since I did those kinds of shutdowns they have replaced some of it.

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  • [–] 1 point 9 months ago

    Yeah modern stuff still has lots of wires. An automated valve may have 4 or 5 wires - open command, open feedback, closed feedback and 0V.

    A switch to show something is open or closed will have two wires.

    You can put a lot of that stuff on a fieldbus but that is often trading lower install costs for higher ongoing costs and more downtime.

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  • [–] 28 points 9 months ago

    For one, redundant systems. For another, lots of sensors. Electric generation also has a whole lot of important things going on that take tons of cabling. Burning the coal is the easy part. Grid phase alignment and a host of other fun things need to happen quickly and in a coordinated way with failovers and data lines to multiple separate places.

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  • [–] 7 points 9 months ago (3 children)

    Having less compute may mean even more cables: rather than having data sent over one cable then decoded, each line is either on or off, controlling: something.. (there could be signals here just contemplating). In modern stuff the logic is condensed, with data running between, in effect these older systems were one distributed logic unit. Probably over simplifying hut think of an old motorcycle, many cables, because you have to run power and ground back and forth all the way from switches to lights motors etc and back again.

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  • [–] 1 point 9 months ago (2 children)

    Right, but even taking that into account, how many control signals could the thing possibly need?

    If I enumerate every possible signal I can think of that a coal plant might need (boiler temp, fire temp, turbine speed, water flow, fuel hopper door control, etc.), and then arbitrarily multiply by an order of magnitude, my estimate is still lower than the number of wires I see in the pic.

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  • [–] 4 points 9 months ago (1 child)

    I'd take each of your metrics and multiply it by 10, and then multiply it by another 10 for everything you haven't thought about, then probably double it for redundancy.
    Because "fire temp" is meaningless in isolation. You need to know the temperature is evenly distributed (so multiple temperature probes), you need to know the temperature inside and the temperature outside (so you know your furnace isn't literally melting), you need to know it's not building pressure, you need to know it's burning as cleanly as possible (gas inflow, gas outflow, clarity of gas in, clarity of gas out, temperature of gas in, temperature of gas out, status of various gas delivery systems (fans (motor current/voltage/rpm/temp), filters, louvres, valves, pressures, flow rates)), you need to know ash is being removed correctly (that ash grates, shakers, whatever are working correctly, that ash is cooling correctly, that it's being transported away etc).
    The gas out will likely go through some heat recovery stages, so you need to know gas flow through those and water flow through those. Then it will likely be scrubbed of harmful chemicals, so you need to know pressures, flow rates etc for all that.
    And every motor will have voltage/current/rpm/temperature measurements. Every valve will have a commanded position and actual position. Every pipe will have pressure and temperature sensors.

    The multiple fire temperature probes would then be condensed into a pertinent value and a "good" or "fault" condition for the front panel display.
    The multiple air inlet would be condensed into pertinent information and a good/fault condition.
    Pipes of a process will have temperature/pressure good/fault conditions (maybe a low/good/over?)

    And in the old days, before microprocessors and serial communications, it would have been a local-to-sensors control/indicator panel with every reading, then a feed back to the control room where it would be "summarised". So hundreds of signals from each local control/indicator panel.

    Imagine if the control room commanded a certain condition, but it wasn't being achieved because a valve was stuck or because some local control over-rode it.
    How would the control room operators know where to start? Just guess?
    When you see a dangerous condition building, you do what is needed to get it under control and it doesn't happen because...
    You need to know why.

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