There is a usual relation to calculate impedance Zo = sqrt ( (R + 2 * pi * f * L ) / (G  + j * 2 * pi * f * c) ). G part  is small and it can be neglected. Equ. become Zo = sqrt ( R / (j * 2 * pi * f * L)). Regarding cable`s active resistance @50Hz wouldn`t change due to the freq change. You could calculate X part in depend of f, upon L value @50Hz (this is the data that`s given from the manufacturer). When f becomes large enough, resultant equation is:  Zo = sqrt ( (j * 2 * pi * f * L) / (j * 2 * pi * f * C) ) Which can be simplified to the form:  Zo = sqrt ( L / C ).

The rest is EXCEL formula editor + copy/paste to the various area sizes of cables. Respected harmonics are whole multiples of 50 and you can even calculate it by the terms of harmonic number. Method should be relatively reliable. Depending weather you are doing lab research. 1st mentioned equ. should be good enough because your harmonic no. is less then 15th and it`s f is 750Hz. (If you have UPS supply for example)

Note: R dependences upon the temperature. Should be considerable. This U can also get from manufacturer. If not U can also calculate it upon cable core material.Regarding manufacturer you can always use grater section of a cable, spend some more money. But that’s what we do NOT want. That`s why we are here.Kind regards,Vlada

It is available the R  L and C parameters from all big cable campany like Batt  http://www.batt.co.uk/  or Prysmian http://www.uk.prysmian.com/en_GB/cs/index.html  If you can't find proper information in the technical information secton on the website, thats available on regvest You can get also information about the electrical parameters of the cable shield at armoured cables, its important if you using the armour as protection conductor.

 Kind regards, Gyorgy