# Re: HOW TO MEASURE XFRMR POWER?

• To: tesla-at-grendel.objinc-dot-com
• Subject: Re: HOW TO MEASURE XFRMR POWER?
• From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
• Date: Tue, 27 Feb 1996 08:31:28 +1200
• >Received: from rata.vuw.ac.nz (root-at-rata.vuw.ac.nz [130.195.2.11]) by uucp-1.csn-dot-net (8.6.12/8.6.12) with ESMTP id MAA26873 for <tesla-at-grendel.objinc-dot-com>; Mon, 26 Feb 1996 12:30:10 -0700

```Hi everybody,
A suggestion on this....

> I have 2 12KV transformers.  They are about 2.5' cubed and filled with oil.
> I
> have been able to tell the output voltage by placing 10VAC on the input and
> measured 1200VAC on the output.  The tricky part is how to tell what the powe
> r
> rating is.  There is no indication of who made them or any stickers or plates
>  on
> them of any kind.
>
> Does anyone have any ideas on a semi-easy way to tell what the maximum safe
> power output of the transformers are?

Connect a capacitor across the secondary of one of them, connect a LOW
impedance signal generator across the primary, then use a scope
connected across the capacitor and secondary to find the resonant
frequency. If you don't have an oscilloscope, you find resonance
easily enough by connecting a neon bulb across the
secondary/capacitor.
Knowing the value of C and f, calculate Xc by

Xc = 1/(2xPIxfxC)

This value will be = to Xl of your transformer. Since you know
that V = 12kV, you can calculate I = V/Xc  which you can then
calculate a ballpark W = VxI from. You can also calculate W = V^2/Xc.
I think this should get you pretty close.

Malcolm

```