RE: Current Shunts

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Steve Conner" <steve.conner@xxxxxxxxxxx>

>They have other shunts for the same price , but this is what we nead for TC
work

I know this is just going to start a debate. I think current shunts have
their place for driving a meter to read DC bus current in SSTCs and
spark-gap DC coils. But I would _never_ use one for looking at TC primary
current with a scope. Hell would freeze over, the sun would rise at
midnight, and Michael Moore would be President before I even thought about
it. I would always use a ferrite cored current transformer or a Rogowski
coil.

The reason is that these can be electrically isolated from the circuit that
you're measuring. You can wind the primary with thick HV cable. They can
even be Faraday shielded to screen out noise. On the other hand a current
shunt has to connect straight to the power circuit and then you're trying to
separate about 1 to 10 volts of wanted signal from a 400 volt high frequency
unwanted signal. ("common mode" is the EE jargon term for this unwanted
stuff)

And that's in a SSTC. In a spark gap TC that 400V common mode signal is
nearer 15,000V. Unless you're lucky enough to have a power supply (like a
pole pig or potential transformer) where the end of the circuit containing
the shunt can be grounded.

I'm sure it can be done. I have seen researchers at the university use a
special custom shunt to measure 10,000 amp simulated lightning discharges.
(And I seem to remember they couldn't get an accurate signal because of
common mode effects) But for measuring TC primary currents it's so much
easier to throw some left over secondary wire round a piece of plastic
tubing or ferrite ring.




Steve C.