Frequency-Dependent Line Parameters of an XLPE Power Cable Relating to Geometric Variations

In diagnostic simulations, impedance changes as failures or as other changes are mostly freely chosen, with respect to their magnitudes or rates of change. The freely selected rates are based on individual backgrounds and opinions. For massive failures, this type of fault approach is possible. However, smaller impedance changes, distortions or geometric variations, are more complicated because of the lack of sufficient background or bases for data. Therefore, this study investigates possible geometric changes, as small changes, for further diagnostic methods which require the changes of the transmission line parameters for diagnostic evaluation. A possible diagnostic method is Line Resonance Analysis. Line Resonance Analysis is a diagnostic method which can maybe evaluate small impedance changes at a local cable position. To evaluate this claim, small impedance changes are needed. Hence, this work deals with geometric changes where the cross section of a cable varies as a result of external pressure, installation or manufacturing issues or needle insertion. The required studies are undertaken using a finite-element simulation. The simulation represents the cable cross section of a medium-voltage power cable using a 2D model and a high order of complexity. The model varies the cross section of the cable and calculates the line parameters for different variations in a frequency range from 1 mHz up to 100 MHz. The results are expressed via the line parameters in 3D plots. The plots show small changes of the line parameters with realistic geometric variations.