Limiting the cable inductance

The design of a shielded twisted pair cable requires max values of capacitance 120 pf/mt and max. value of loop

inductance 0.68 uF/mt  over a length of 300 mts. Conductor is 22AWG and the shield type is copper braid.

We are considering TPE insulation. Can anybody suggest the insulation thickness and other relevant

parameters to achieve the above values?

I am not an expert in this field, but I guess basic electromagnetic theory could help us to solve this problem.

The inductance per meter of a cable can be calculated analytically or simulated numerically based on the structure, dimensions, permittivity and permeability of the insulation material of the cable, therefore, we can adjust the design to meet the required specification based on the calculation result.

Hello Srinivasan! Happy New Year!

Please use the pdf link below:
https://www.digikey.com/Web%20Export/Supplier...eDesignEquationsBalancedPair.pdf?redirected=1

Just be careful because the units are in pF/ft and the requirement is in pF/mt.
From the table, TPE would have a permittivity of 5 so all you have to do is
design the diameter of the conductor, the diameter of the insulator, and the
number of strands to fit the 120 pF/mt specification.

If all else fails (I hope it does not), you can design 1 cm. long shielded twisted pair cable test samples with different diameters and measure their capacitances (though
I think you'd be needing a high-end multimeter for this one like an Agilent 34411A, and I'm not even sure if it's possible).

Anyway, I hope this helps.

Justin

I am aware of this formula for capacitance.
The issue is Loop inductance(L) which , we know is inversely proportional
to Capacitance. I don't find a proven formula for L.
The permitivity for TPE is about 2.6 as per datasheets of Exxon, Teknor etc.