Re: determining transformer characteristics

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Mark,

If you just want to measure transformer inductances, that is easy.  Just
power up the primary with nothing attached to the secondary and measure the
current going into the primary.  Only the primary inductance is limiting
the current (close enough).  So if you have a 240VAC pig that draws 1/4 amp
with the secondary open:

V = I x R    240 = 0.25 x (960)

Rl = 2 x pi x f x L   960 = 2 x 3.14159 x 60 x (2.546uH)

If it is a 240 to 14.4kV pig, the winding ratio is 60:1 and the secondary
to primary inductance is 3600:1 so the secondary is 9165H.  Don't let those
giant Henry numbers bother you.  Typical for big high voltage transformers
:-)) Hard to find meters to measure that ;-))

Real meters and super science will get closer numbers, but these simple
values get really close for modeling work.  You can go to more complex
models but that is typically not needed for most purposes.  You may want to
measure the DC resistance and add that in series with the windings
especially for MicroSim that has problems with "perfect" components that
ignore losses.  You can play with the values a little in MicroSim to
"adjust" things if needed.  You can do similar stuff with the secondary but
try to use real voltages so the core is saturated enough to be realistic.
I always see people trying to measure the inductance of 1000+ pound
transformers with hand held 9-volt battery LCR meters :-))  They whine
because it looks shorted...  You need "real" currents to get that 1/2 ton
of iron to act like an inductor...

This stuff is not as super cool as Tero's work, but I hope this is what you
were looking for.

Hey!, I can work at Dairy Queen these days and make 3$/hr more that I
started for in engineering :-))  Start cheap and your brains will quickly
suck you into the giant "brain void" at the "top" ;-))  Some people thing
Dilbert is "just" a cartoon rather than a way of doing real business...

Cheers,

	Terry


At 03:30 PM 7/18/2001 -0500, you wrote:
>Terry,
>
>thanks for posting those links.  I had seen them months ago, but lost their 
>addresses.  However, I was wondering if there was a way to perform similar 
>calculations on a non-current limited transformer (PT, MOT, pig)?  
>I have a couple transformers I would like to simulate accurately.  I could 
>measure them, but that would mean buying a Henry meter capable of reading 
>perhaps 10kH (and it's gotta read the .1uH, too :-).  Of course 
>just graduating with a BS and still looking for a job (what a wonderful 
>economy to graduate into!) means I can easily afford one......  (at least 
>I'm not terribly discouraged yet)
>
>Thanks,
>
>Mark Broker
>
>7/18/01 2:13:00 PM, Tesla list <tesla-at-pupman-dot-com> wrote:
>
>>Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>>
>>Hi Mark,
>>
>>Check out these wonderful papers by Tero Ranta:
>>
>>http://hot-streamer-dot-com/TeslaCoils/OtherPapers/TeroRanta/CurrentLimitedTrans
>>formers/NSTModel.htm
>>
>>http://hot-streamer-dot-com/TeslaCoils/OtherPapers/TeroRanta/NSTCapMatching/Reso
>>nantCapacitorMatch.htm
>>
>>Cheers,
>>
>>	Terry
>>
>>At 10:43 AM 7/18/2001 -0500, you wrote:
>>>List,
>>>
>>>Although my uses for this information is not directly related to Tesla 
>>>Coils, the information IS directly useful to TCs.
>>>
>>>Without the aid of a Henry meter, I would like to determine the inductance 
>>>for a tightly coupled transformer.  I've run across an excellent paper on 
>>>the Net that explained how to calculate the inductance of an NST.  This 
>>>proceedure involved shorting the secondary while mearsuing the primary 
>>>current.  On a loosly coupled transformer, like an NST, this proceedure 
>>>works sufficiently well.  On a tightly coupled transformer (PT, pig, high-
>>>power MOTs), this proceedure won't really work.  Is there a way (without a 
>>>Henry meter) to find the inductance of a tightly coupled transformer?
>>>
>>>Also, can anyone hazard a guestimate as to the coupling coefficient of a 
>>>500VA, 2:1 toroidal transformer?
>>>
>>>Thanks,
>>>
>>>Mark Broker
>>>
>>>
>>
>>
>>
>
>
>