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From: dc@hpmtlx.HP.COM ($Dave Crook)
Newsgroups: sci.electronics
Subject: Re: How efficient are transformers?
Message-ID: <880004@hpmtlx.HP.COM>
Date: 11 Apr 89 19:01:49 GMT
References: <731@hutto.UUCP>
Organization: HP Manufacturing Test Division - Loveland, CO
Lines: 35

/ hpmtlx:sci.electronics / larry@kitty.UUCP (Larry Lippman) / 10:31 pm  Apr  9, 1989 /
In article <731@hutto.UUCP>, henry@hutto.UUCP (Henry Melton) writes:
> Does anyone have any definitive numbers on the efficiency of
> transformers?  in particular, the ones on the poles outside the house.
> I was having a discussion with a friend the other day and he was
> claiming that upcoming improvements in core material would increase the
> public power distribution system efficiency by large (10%,20%) amounts.
> I was under the impression that the gadgets were already so efficient
> that there wasn't that much headroom to play with.  

>>  	High-voltage distribution transformers are more efficient than
>>many would believe, and in general, the efficiency improves as the kva
>>rating increases.

>>	  A typical single-phase oil-filled pole-mounted transformer rated
>>at 10 kva has an efficiency around 97%.  As the kva rating increases,
>>the efficiency generally peaks out around 98.8% at 200 kva and above.

In many cases, especially in residential lines, the losses in the power 
lines themselves are far greater than the losses in the transformers.
If the transformer does not have large heat radiating tubes or fins, the
chances are that it is quite efficient.  Since all losses are converted
to heat,  the heat dissipating sinks are a directly measure of the losses
the transformer was designed to dissipate at maximum load.

   Many "transformers" are actually transformer regulators.  Inside the 
"transformer" is an electronic voltage detection circuit which controls
the voltage ratio.  Under heavy loads the ratio increases which compensates
for significant voltage and power loss in the power lines feeding the 
transformer.

Dave Crook
Manufacturing Test Division
Hewlett-Packard
Loveland, Colorado