Coil's DC resistance.

[alphacat]

Hello.

I have a CT here.
The Coil's DC resistance is Rs (42Ω).
The coil's reactance is XL (ωL).
I connect a burden resistor Rb (100Ω) at the output of the secondary winding.

If the secondary coil is to generate Io, then the output voltage would be:
(Rs || Rb) * Io
?

If so, Why shouldnt we take into account XL when calculating the output voltage?

Thank you.

 

[crutschow]

What's a CT, a control transformer?

A transformer's inductance determines the magnitude of its exciting current. It is not seen by a load on the secondary.

 

[alphacat]

Hi Carl.

CT is a current transformer.
It has only one coil wrapped around a magnetic core.

Isnt XL also kind of an "ohmic resistance" since it has units of ohm?
So why dont we take it into account when calculating the voltage drop on the burden resistor?

 

[crutschow]

I should have known that.

XL is in ohms, but it is reactive ohms.

The inductance (which generates reactive ohms) is simply a measure of the coils inductance for reference purposes. It has no direct effect on using the coil as a current transformer. It is not seen by the secondary when the transformer is performing the transformer function. That is because any magnetic flux generated by the current in the primary is canceled by the magnetic flux generated by the corresponding current in the secondary. Since these primary and secondary fluxes cancel each other, there is no inductive effect. There can be some inductive effects due to small leakage inductance, but that is usually negligible at low frequencies.

 

[alphacat]

Thanks a lot Carl!