At 03:39 PM 8/20/99 -0600, POWELL, DOUG wrote: > >Hello all, > >I have a very innovative engineer who has come up with a design idea that >uses concrete as an insulating compound in a very large inductor for a 200 >kW switching power supply. Yup, this is the stuff you buy down at the local >building supply company. He was very proud of the idea, but until he came >up with it I think he was pretty desperate. I'm thinking I should make him >desperate again but would like to be able to give him a clearly reasoned-out >explanation. > >Has anyone ever had experience with using concrete or mortar in a high >voltage application? What are the concerns here? It is my understanding >that it does not actually "dry" but it cures with all the water contained >inside.
Been following this interesting discussion, and I have a few concerns to raise. Maybe someone could possibly set me straight since that seems to be happening a lot lately. <cough> First as has been stated, concrete floors are great for conductive areas. But I believe with the quality checks I did at another company, we're talking in the megohms. But there's a lot of buts that go along with that. Second, I was surprised to find that concrete has nearly the same linear expansivity as copper! Glass on the other hand is way off. So that turned out to be not a concern. Third, is the obvious thermal insulation properties. I'd be concerned about that at elevated temps. Fourth, is an odd thing that effects concrete structures. Apparently well known in civil engineering circles. Not me so don't ask. It's called "Alkali Silica Reaction" (ASR). Otherwise goes by the common name Concrete Cancer. Over time, concrete structures can eat themselves up from the inside. So I'd definitely get in touch with one of friendly Civil Engineers to find out more about it. Fifth, I believe that since concrete is alkaline in nature a low reactivity with rebar happens. So I don't think you'd have a problem there. Sixth, I believe that concrete is hydrophilic and loves water. And yes, it does not "dry". I was making a stone wall along a brook long ago. A mason (who had been a friend in high school) came by to give me some pointers. I wanted to set some of the base stones in concrete but they were to be below the water level. "Just do it" he said, explaining it was chemical reaction taking place and not just a simple wet mixture drying. Lo and behold, it worked. So I'd be careful if this construction is to be subjected to high humidity. It would seem to me that the concrete would "breath" humidity at a certain rate much slower than expected. Seventh, concrete is excellent for compressive loads. Not tensive. Eight, vibration. Have not a clue on that one. If you're doing Bellcore, definitely check into that one. Ninth, properties of concrete depend greatly upon the aggregates used (cement) and it's proportion to water when mixed. If you want repetitive results, mixing may have to be an issue for strict procedural control. Otherwise, it's left wide open for anyone to assume. Regards, Doug --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
