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  1. Stephen Nuchia

    Confessions

    I still chuckle about this every time it crosses my mind ... a tire plant that has since been re-tired (ha!) had been built during a labor dispute. I don't know all the history but there were some dicey things in there. One Christmas I had to open every load box on all the miles of overhead LV...
  2. Stephen Nuchia

    Confessions

    I don't have any good design error stories to tell but I've failed to recognize the flaws in systems for too long a few times. One plant we worked in had an "old" and "new" medium voltage network with a few big medium voltage motors and a lot of 480v, fifteen or so substations. The...
  3. Stephen Nuchia

    Confessions

    I set my brother on fire once. He was about 6, walked into my "lab" while I was doing something pointless and destructive with a gasoline torch of my own devising: a little gasoline in a test tube with a stopper and a 90 degree glass tube through the stopper. Heat it briefly over the Bunsen...
  4. Stephen Nuchia

    Estimating inertia on old machines for adding electronic braking

    I never worked on the calendar machine controls directly but I did switchgear maintenance in a couple of tire plants. The calendars are a lot bigger than a pickup truck, think something closer to a modest newspaper press. The good news is that for this kind of machine the stopping inertia is...
  5. Stephen Nuchia

    Miami Pedestrian Bridge, Part VII

    "to get a PE one basically has to find a job working under the supervision of a PE for a significant period of time" yes, that's the main pipeline and for good reason. I happen to have spent most of my career working solo on software so while I passed the POE I never had enough documented...
  6. Stephen Nuchia

    High Resistance grounding on Medium Voltage System

    How are your feeder relays deriving their ground fault indications? Do you know how the relay scheme was tested at commissioning? I could tell stories ... Were the lightning arrestors speced for 4kv or 7kv? That's one of the stories that comes to mind. Old plant added new utility feed with...
  7. Stephen Nuchia

    Question Regarding Motor Starting Current and Power Source

    Starting current is what happens when you apply full voltage to a motor with no rotor magnetization and no rotation. There's no "back EMF" (I guess that's an obsolete term now?) and it draws whatever the combined impedance of the supply and the windings will allow. Usually pretty much the same...
  8. Stephen Nuchia

    heat storage system fudge factors

    Thanks! I saw a version of that computation but without real-world application context or numbers. Having somebody who knows what they are doing turn the crank is reassuring. The surface area is only about 0.3m2, ambient for most of my market will be around 20c worst-case (tropical and...
  9. Stephen Nuchia

    heat storage system fudge factors

    Looks like I might still want to use that "boiler blanket" or something comparable for the lid insulation, disk-shaped vacuum-insulated structures aren't a thing that sounds practical. How can I calculate (or estimate) the heat loss through a vacuum flask? Other than the neck (and possibly...
  10. Stephen Nuchia

    heat storage system fudge factors

    IRstuff, in the systems you've suggested a heated charge of food is enclosed in an insulated chamber and cooks by retained heat over a period of time. This is mainly suitable for wet cooking and requires a conventional heat source to provide the initial heat. In primitive conditions (and in...
  11. Stephen Nuchia

    heat storage system fudge factors

    Thank you racookpe1978, I had been fretting over the mechanical supports I'll need and the thermal path they represent. Steel isn't too bad, it's strong and has high yield strength for a given cross section, but the cooking interface needs to be aluminum (maybe, that's what I've been...
  12. Stephen Nuchia

    heat storage system fudge factors

    Ok, I'll admit it, I'm old enough to have broken a lot of aluminized-glass lunchbox thermos bottles in grade school. Stainless would probably be durable enough, though thermal resistance will go way down if it's dented to the point the inner and outer walls touch, and that would create a safety...
  13. Stephen Nuchia

    heat storage system fudge factors

    Thanks but that's not exactly what I'm doing. And vacuum insulation is too fragile to meet the needs of my target audience. Even in a heavy sleeve it's too vulnerable to shock.
  14. Stephen Nuchia

    heat storage system fudge factors

    Hi, I'm working up a new prototype of a heat storage stove. I'm looking at some "boiler blanket" insulation material that is some kind of high-temp fiber matrix with aerogel embedded in it. Details are alibaba-obscure. Anyway, they provide a thermal conductivity versus temperature curve that...
  15. Stephen Nuchia

    Miami Pedestrian Bridge, Part V

    chris snyder near the end of thread IV sketches a counteracting compression force from the first diagonal of the south span. I believe that is a misunderstanding. In a cable-stayed bridge the ends of the span would indeed thrust against one another at the central bearing. But this is not a...
  16. Stephen Nuchia

    Miami Pedestrian Bridge, Part III

    @gwideman, Sheet B-8 of the proposal package (linked from thread 1) shows some kind of bolt there but it looks like it's for position-keeping rather than tension.
  17. Stephen Nuchia

    Miami Pedestrian Bridge, Part III

    In a post near the end of thread II I mentioned the appearance of something moving spanward from the position of column 12. Further review estabilishes that as a structure in the far background coming into view from behind the column and the crane boom in front of it (dashcam view). Just...
  18. Stephen Nuchia

    Miami Pedestrian Bridge, Part II

    This is speculation of course but a theory of the failure I've not seen yet in this thread is sheer failure at the interface between 11/12 and the deck. In the dash cam footage there appears to be motion of 12 spanward as hinging starts to develop. But the base of 12 remains on the pylon so it...

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