Help with variable transmission line

[yneh]

Hello!

I would like to know if there is a good way to construct a variable inductance and capacitance for 230 V. Basically what I wan't do make is a gyrator-c circuit for 230 V /60 Hz. (or something like it).

The reason for this is that I would like to make a lumped PI-link transmission line emulation where I can tune the length of it and later on observe the effect (voltage drop and phase shift) by varying the length. I got a three phase 400 V/60 Hz input to my disposal.

I have been looking at different techniques involving switching, but that generates harmonics and distorts line currents, which isn't what a real transmission line does...

 

[chuckey]

The variable inductor can made using a core with a curved B/H curve, you have the main "inductance" winding and a second winding through which you pass DC. The DC shifts the operating point up and down the B/H curve. This is used for magnetic voltage stabilisers. Expect 2-3% distortion. Once you have a variable L, just put it in series with a fixed C of greater reactance and you then have a variable C. Run this experiment at low voltage, using 440V with resonant circuits will lead to flash overs and explosions.
Frank

 

[mtwieg]

What kind of power levels are you going to put through the line? If the power is high then you probably have no choice but to use true switched or variable inductors. One thing that may work is if you use a simple variac as a variable inductor (using just the wiper terminal and one end terminal).

 

[yneh]

What I'm exactly trying to do is this: Imagine a PI-link "filter" with fixed values. By using my three phase as input I can observe a attenuation and phase shift of the output voltage,and current. What I am trying to accomplish is to make this "filter" tunable, where the RLC parameters are scalable with what length i'm putting in the system.