Transmission Line Calculator March 6, 2007
A cross section of the transmission line is drawn into the Excel grids using different colors to represent the conductor, shield (return), and insulator. A finite element model of the transmission line is then solved with 1 Volt applied to the conductor with respect to the shield. The voltages throughout the insulator are found. This allows the stored energy, capacitance, inductance and impedance to be found.
Each grid of the insulator can be thought of as 4 capacitors each having a capacitance per unit length of 2*Eo*Er where Eo is 8.854 pF/m and Er is the relative permittivity of the material (see figure below). Once the total capacitance is found, the inductance per unit length is then:
L = Mu*Eo*Er/C (in nH/m)
where Mu = 1257 nH/m
And the impedance is then:
Z = SQRT(L/C)
1. RIGHT-CLICK, download, and save this file on your computer:
(Left-Clicking and/or Opening in browser DOES NOT WORK.)
2. Close any open instances of Excel that are running on your computer.
3. After saving, open the file. It contains macros, so you may see a warning. Macros must be enabled for it to work.