|> |> I assume you meant 230 volts. |> | | The furnace is powered by a 3 phase transformer which steps down 380V | to 23VAC -(twenty three) 3 phase @ 55Amp. (low voltage high current). | | regards
OK, my bad.
That's not actually that high a current for a furnace. That's only
1265 watts per phase, for a total of 3795. The electric blast furnaces I've seen are measured in megawatts.I'll make another assumption and assume the power coming in is 380V between phases, 220V between phase and neutral. And I'll assume that your transformer is connected with all three primaries in a delta where each connects between two phase wires (e.g. you have neutral coming in, but it's not used for the transformer primary). That means when one phase wire is disconnected, one primary still gets 380V but the other two are now in series across the two phase wires that are still energized. The end result of this is that one set of elements is working on the full 23V while the other two are only getting 11.5V. Dismissing resiatnce variation due to temperature (which cannot really be dismissed) you're only getting 1265 watts from the hot element, and
316.25 watts from each of the two warm elements, for a total of only 1897.5 watts, half of what you need.You can still correct this. But the best course depends on whether they disconnect the same phase every time, or disconnect a randomly chosen phase. If they are doing phase disconnection as a means to do a "rolling blackout", they you'd have to consider it to be random. A triple delta secondary would fix it, but it would also backfeed the power lines where everything else that was power on that phase will probably end up pulling way too many amps and blowing all the fuses.
You probably don't need three phase to run the furnace. You could hook all three elements to the same phase. But your transformer that converts 380V to 23V might be one designed with a three-phase "E" core, which cannot be run on single phase. If you had three separate 380V to
23V transformers, you could just re-wire (or use transfer switches) to get power from whatever phases are live. Of course you'd have to make sure your circuit capacity on each phase is sufficient to run everything from just 2 of the phases.--
----------------------------------------------------------------------------- | Phil Howard KA9WGN |
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