William,
Well you can somewhat but if they didnt use the right size of wire, it will
affect the power capibilities too. I've seen some try and get by using 500 cir
mils per amp which is too small for ICAS in my opinion. Most books on the
subject recommend at least 700 cir mils and up for ICAS, or 1000 and up for
CCS. That's the catch 22 in transformer design, or the ones that size the
transformer by power handling, which are the cores area in sq. cm, / sq inches,
and the wire size. You could have a large enough core but the wire size be to
small to handle the current. Or, it could be vice versa. It takes about 5 -
5-1/2 sq inches of core for 1 kW but doubling the size dont add up for 2 kW as
its logarithmic so what ever core size he has, it would have to be calculated
from it along with finding out if the wire would handle it. That's the only way
I know to properly size it and say which it is.
If it's made with a conventional stock lam, one can look up the height and
width of a lam to find the lam size. This wont give the center leg dimension as
some aren't X2 the outer leg but thinner. After the leg width is found from a
spec sheet, then do a quick measurement of the stack thickness. Multiply the
thickness by the center leg width and get the core area. A little math will get
you close but you wont be able to know what the maximum flux density is without
knowing the type of steel. For unknown types, I was taught to always us 12
kilogauss or 77,400 line per inch. If you knew what it was, it could be as high
as 15 kilogauss +. A stacking factor of about 0.9 can be used for EI lams which
are interleaved. That's about as close as one could get it.
To figure the core area at 60 Hz and at 12 kilogauss, this will get you in the
ball park;
0.16 X sqrt of P
P = power in watts
for 1000 watts;
0.16 X sqrt of 1000
0.16 X 31.6228 = 5.0596 sq inches at 12 kilogauss
The two measurements he made in resistance do help to determine the copper
losses though. If one knew the steel type, the iron loss could be looked up,
and after adding all together, have the total losses of the transformer and
know its efficiency.
Best,
Will
*********** REPLY SEPARATOR ***********
On 4/29/05 at 6:08 PM Dr. William J. Schmidt, II wrote:
>Can't you just measure the core cross-sectional area and use a formula to
>get a rough idea?
>
>Sincerely,
>
>Dr. William J. Schmidt, II K9HZ
>Trustee of the North American QRO - Central Division Club - K9ZC
>
>Email: bill@wjschmidt.com
>WebPage: www.wjschmidt.com
>
>"If computers get too powerful, we can organize them into a committee;
>that
>will do them in." -- Bradley's Bromide
>
>
>----- Original Message -----
>From: "Will Matney" <craxd1@ezwv.com>
>To: <amps@contesting.com>
>Sent: Friday, April 29, 2005 10:28 AM
>Subject: Re: [Amps] Plate transformer current unknown
>
>
>Angelo,
>
>Really you cant tell that way (using the resistance) unless you know the
>mean lenght of turn, how many turns per layer, and how many layers they
>are
>in the winding. This then would give you how long the wire is and you
>could
>then use the resistance and the length to determine the wire size. If it's
>possible to use a micrometer or a wire gauge to see what the secondary
>wire
>size is, then one can find out what its rating is. In amateur service,
>ICAS
>used anywhere from 700 to 900 circular mils per ampere. CCS uses anyhwere
>from say 1000 to 1200 cir. mil. per amp. If you can find the wire size, go
>look at a wire chart for how many circular mils it has and divide by the
>above numbers to determine its current carrying ability. IE, 10,000
>circular
>mils running at 1000 cir mil per amp = 10 amperes.
>
>Best,
>
>Will
>
>
>*********** REPLY SEPARATOR ***********
>
>On 4/29/05 at 3:01 PM Angelo Karabetsos wrote:
>
>>I would like to find out the current rating of a transformer. Primary
>>voltage taps 0v-110v-115v-208v-230v and secondary taps 3450v-0v-3450v and
>>secondary resistance of 53.5ohms from 0v to 3450v tap and 107ohms from
>>3450v
>>to 3450v tap. All measurements done with a simple DMM. The commercial
>>amplifier it came out of has a plate current meter with a max reading of
>>600ma. How could I find out the CCS or ICAS rating?
>>Cheers Angelo
>>
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>
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