Peter Chadwick wrote:
> David said:
>
>
>
> >I can't really see how you could determine the temperature rise too
> >easily by this.
>
> If it doesn't get too hot on open circuit, the iron losses aren't too
> high.
But then any transformer that gets too hot open circuit is suspect. I
guess if you run the input voltage too low, or run it at 50 Hz when it
is designed for 60Hz, then it might get too warm then.
> If it doesn't get too hot on short circuit, the copper losses
> aren't too high.
But when you put it into a short circuit, you only have the copper
losses, not the iron losses.
Each on their own might not be too much, but get them together and its a
different story. That was what I thought was the point of the short
circuit open circuit tests - one gave you the copper losses, the other
the iron losses.
I have some recollection from when I did me EE degree, that for maximum
efficiency,
copper loss == iron loss.
But the old brain cells have no doubt suffered a bit since then, and
since I have never worked professionally with power transformers, I
could well be wrong.
But personally, I'd sooner stick it on a load.
> Probability is that it won't get too hot in service. Rough and ready
> tests; most transformers seem to get hotter under load, suggesting that
> copper losses predominate.
No, I disagree. The fact transformers get hotter under load just proves
there are copper losses. It does not prove they predominate.
> Time to worry is when the pitch or resin or whatever bubble
> out.......messier is the oil filled xfmer where the pressure leads to an
> oil leak....
--
David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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