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Scope pictures of my TC: how I did it
Last saturday I measured my TC with a scope. I got:
- primary current
- primary voltage
- secondary voltage
- secondary base current
A great simplification was that at the laboratory were I performed the
measurements they had a really huge ground (it's the Helsinki High Voltage
Institute). This means I could use the same ground for everything,
including secondary, tank and oscilloscope.
Primary and secondary (base) currents I measured with a "current
transformer" (a toroid you just pass through the wire carrying the current
you want to measure). As it is a CURRENT transformer, you need also a shunt
to generate a voltage to measure at the secondary of the transformer: note,
you are galvanically isolated from the circuit you are measuring.
The primary voltage I measured directly with a HV probe (10 kV,
Tektroniks).
For the secondary voltage, even if they had plenty of capacitive and
resistive dividers they were all in use that time and the target of my
measure was more to find out about power consumption than to have an exact
measure of secondary voltage. So I used the simple 10:1 probe connected to
nowhere and hanging at about 180 cm from the toroid: I was reading there
about 50 V (!). That gave a measure of the electric field (I guess)
magnitude and, thus, indirectly of the secondary voltage.
This seemed to be true only if there were no streamers: if a streamer was
born, the secondary current would oscillate down as expected but the
"electric field" would drop down suddenly to zero. I guess that the
explanation could be that the streamer loading dumps the electric field (or
RF emission?) so that you can't measure it anymore with the flying probe
(you need to really go and touch the toroid).
But more in the near future...