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RE: OLTC Measuring Peak Current

Original poster: "Derek Woodroffe" <tesla@xxxxxxxxxxxxxxx>

	The stainless steel strip is a good idea, but in the primary of a
small OLTC (even in a larger one) any current measurement that adds 1" to
the primary circuit will also introduce a large (for an OLTC) amount of
inductance. This will have two effects,

1. The calibration is going to have to take this inductance into account.
2. If the bar is removed the readings that have been taken will no longer be
true because you have removed the extra inductance from the circuit.

	I think the best way to get a rough current reading is to add a
ferrite E core around your primary feed, and make a simple current
transformer. With the ones I have made I get about 5-10% accuracy which is
enough for checking if you silicon is going to explode.

There is of course the added inductance of putting a ferrite in circuit, but
I think this is less than the additional length of primary feed.

I actually think you are trying to measure the wrong thing. If you can
accurately measure the inductance of your primary, w/o the secondary, you
will be able to calculate the worst possible case of current in the
secondary. You can get a fairly accurate measurement of the primary L by
measuring the capacitance in you primary cct with a meter and finding the
frez of your primary & cap with a scope and sig gen. you can them find your
actual value of L from that.

I have tried many ways of calculating the L of an OLTC and I haven't found a
better way yet. But I'm sure someone here has an even better way ?