wrote:

On Saturday, 14 April 2018 14:42:10 UTC+1, The Natural Philosopher wrote:

Most small mains transformers are run very close to core saturation, so
any large transients are likely to be clamped by the transformer.

Oh dear. A pseudo authoritative statement from someone who doesnt know
the difference between voltage and current.

So do you disagree with my claim that small transformers are usually
run close to core saturation at their rated voltage?

Do you disagree with my expectation that grossly overdriving such a
small transformer (with the transient to be measured) will cause its
output to saturate and give an incorrect measurement result?

Saturation results from current flow. If the transformer has a high
impedance across the secondary saturation will not happen. (The voltage
output may not be precise for other reasons, but should be good enough
for the sort of transients that are going to affect a heating element.)



This
could be overcome by putting a resistor in series with the transformer
primary so that it is running at a small fraction of mains voltage.
Have a load resistor on the secondary may improve the performance as well.

Oh dear. Soemone who doesnt understand inductance either.

What exactly do you object to here? A resistively loaded transformer
looks like a resistor (apart from the leakage inductance) so in
conjunction with a series input resistor it will form a reasonable
potential divider thereby moving the operation well away from
saturation.

Please explain.

John
The load resistor will not improve anything. The resistor in series
with the primary will just make accurate voltage measurement impossible
because of the poorly defined and frequency dependent primary impedance
while providing no benefits.

--

Roger Hayter