[Amps] Transformer Calcs

[Patrick Barthelow]

For a KW level  HV transformer, is there much difference between the temp that you can touch and measure, say at the outside laminations, and perhaps the more important temperatures in the core center, and the copper wire, bobbins, windings, and paper/plastic insulation materials that we cannot see, inside?

 

And, a related question, from a cold room temperature start, if you could measure the surface temperature of the laminations of a, say, Heathkit SB 220 amp that was being used with a lot of transmit time, on CW at 1KW out,  How long would it be before the outside lamination temperature could give a representative temperature of the more critical inside core temperatures?    Could  there be, say, 50 degree F temperature difference between inside and outside when the Amp is producing 1KW RF output?  If you can cool the outside of the transformer with continuous airflow from a  muffin fan, or better, would that reduce significantly the inside core temperature?


Best Regards,   
73, de Pat Barthelow AA6EG
 

> From: dezrat1242 at yahoo.com
> To: amps at contesting.com
> Date: Fri, 11 Jun 2010 09:57:59 -0700
> Subject: Re: [Amps] Transformer Calcs
> 
> ORIGINAL MESSAGE:
> 
> On Thu, 10 Jun 2010 19:24:58 +0100, "Dr. David Kirkby"
> <david.kirkby at onetel.net> wrote:
> 
> >Personally I would have thought just because a transformer is not too hot to 
> >touch, it would not be safe to assume it is ok. I've run many transformers up to 
> >their maximum ratings and they are nowhere near being too hot to touch.
> >
> >The perception of too hot will also change with person. I recall once finding a 
> >radiator too hot to touch, but someone else could hold their hand on it 
> >continuously.
> 
> REPLY:
> 
> I stand by what I said. Heat is the enemy of transformers because it
> deteriorates the insulation. I agree the concept of "too hot to touch"
> varies from person to person, but not that much. Transformer ratings
> furnished by a manufacturer are not an exact science either. Some will
> be conservative and some not. 
> 
> Run your transformer cool and it will last a long time. Run it hot and
> get ready to buy another one.
> 
> 73, Bill W6WRT
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