Re: Coupling coefficient of industrial transformers

On 9 Apr 2007 09:48:54 -0700, "orvillefpike" <orvillefpike@xxxxxxxxx> wrote:

On Apr 8, 1:41 pm, The Phantom <phan...@xxxxxxx> wrote:
On 8 Apr 2007 12:46:42 -0700, "orvillefpike" <orvillefp...@xxxxxxxxx>
wrote:





On Apr 8, 12:18 pm, The Phantom <phan...@xxxxxxx> wrote:
On 7 Apr 2007 09:24:14 -0700, "orvillefpike" <orvillefp...@xxxxxxxxx>
wrote:

Would anybody know what is the coupling coefficient of step-down,
commercial type, transformers like the ones used in shops, like a
three phase 15 Kva or a 30 Kva?
Thanks

I can't speak to the size transformer you have cited, but a 3 kW single
phase transformer I have on hand has a measured k of .999883

Because I am feeding it with a square wave, the shape and the
amplitude of the output is very different whether the coupling
coefficient is .990or .995.
Thanks

There have been threads on this topic fairly recently.

To measure the coupling coefficient (of an iron core transformer) without
making an inductance measurement, do this:

Apply rated voltage (sine wave) at one winding, and measure the open
circuit voltage at the other, getting the ratio V2/V1'. V1' means that
winding 1 was excited.

Now excite winding two and measure the open circuit voltage at the other
winding, getting the ratio V1/V2'.

The coupling coefficient is very nearly SQRT(V2/V1' * V1/V2')

The turns ratio is very nearly SQRT(V2/V1' / V1/V2')

I just did this measurement on a 25 VA filament transformer and got k =
.99767- Hide quoted text -

- Show quoted text -

Would this method work if I don't feed the transformer at its nominal
voltage, because this transformer was ment to be connected at 600
Volts on its primary side.
Thanks

Because the permeability of the silicon steel core varies somewhat with flux
density, k will vary a little with excitation level, but I think you will get
usable results with a reduced excitation level.
.

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