Due to traveling nature of the transients the modeling of GIS makes use of electrical equivalent circuits composed by lumped elements and especially by distributed parameter lines defined by surge impedances and traveling times. I would like to know how to calculate the surge impedance and traveling times in Gas Insulated Substation for different voltages levels. After calculating how to model these into lumped parameters of R,L,C.
The following link may be helpful to you.
http://maxwellsci.com/print/rjaset/v5-2656-2660.pdf
Suppose there is a transmission line of 20m. I have following data surge impedance is 350 ohms and travel time is 300 m/µsec.
By using the formulae:
Z0 = 60 ln b/a;
C = 2*pi*ᵋ/ ( ln b/a );
L = (µ ln b/a)/(2*pi);
I get L = 1.16µH/m, C = 9.53 pF/m.
Can I now model the transmission line with a pi network of L,C parameters with L= 20.3 µH/m and C= 190.6 pF for simulation.
Its still the same with travelling wave concept on transmission line. Define a wave traveling eq to find the relationship between e and i. And find Zo.
Zo is known as the surge (or characteristic) impedance of the transmission line.
The surge current i traveling along the line is always accompanied by a surge voltage e = Zo i traveling
in the same direction. For a reverse wave, it can be similarly shown that the surge current i is associated with
a surge voltage e = - Zo i.
For the travelling time you can use Lattice diagram. :)
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