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RE: Re: Cascading Transfo
Subject: RE: Re: Cascading Transfo
Date: Fri, 02 May 1997 18:36:00 GMT
From: robert.michaels-at-online.sme-dot-org (Robert Michaels)
Organization: Society of Manufacturing Engineers
To: tesla-at-pupman-dot-com
T> Was reading an article today on new (glass-like steel)
T>magnetic materials for transformer cores. In passing the author
T>mentioned that National Electrical Manufacturers Association (NEMA)
T>specifications on power transformers state that the magnetizing
T>current " must not increase more than 10 TIMES REPEAT 10 TIMES
T>when the primary voltage is increased 10 PERCENT REPEAT 10 PERCENT
T>over the rated value"!!!!!!!!!!!!!!!!!!!!!!!!!! The manufacturers
T>back off from saturation flux density in the core at rated voltage
T>just enough to meet this spec, no more. When you talk about
T>doubling the voltage on the primary you are talking madness!!!
T>I have been reading notes to this effect and can't see how anyone
T>can get away with it. Transformer iron is just too expensive and
T>too heavy for anyone to afford to use more of it than is absolutely
T>necessary.
T>Ed
(1) - You are seriously confusing disparate issues.
NEMA is a civilian agency. It has utterly
=nothing= whatsoever to do with the specs.
for military-contract electrical component
manufacturing.
To put it in naked economic terms, a common-
place transistor might cost, say, $1 in
commercial versions. That same transistor
might well be $30 - $50 in full mil. spec.
grade.
(2) - The cost of transformer iron is vanishingly
small measured against the overall cost of
manufacturing (and testing, and certifying
and documenting) a mil. spec. transformer.
If a critical component (transformer or
otherwise) fails and causes (or contributes
to) the loss of, say, an aircraft carrier
do you think it would be much consolation
to say "well, at least we didn't spend too
much on the iron content"?
- - - - - - -
A small(ish) civilian aircraft (say a King
Air) costs about $ 1/4-million. A Learjet
about $4-million.
A small(ish) military aircraft (say a fighter
plane) costs about $60-million.
Every wonder why that is? (Hint: it ain't
all government waste).
| More to the point and purpose - my suggestion to overrun |
| mil. spec. transformers is =not theoretical=. Try it your |
| self and see. As I've pointed out, the current in to the |
| second transfomer is =much= less than the second trans- |
| would normall draw (1/8th in my example). The NEMA spec. |
| pre-supposes that the current can rise freely with rising |
| voltage. In my example, only a limited amount of current |
| is available from the first transformer - as it happens |
| approximately 1/8 the current the second transformer would |
| normally draw. |
Lovin' my rich "Uncle" in --
Detroit, USA
Robert Michaels