I mainly use the Tower and PLS-POLE programs to analyze the structures but know a little about the line design in PLS-CADD. First, I would say to read the manual and get an idea of where the function is located. Second, I would call their help line and talk to the experts.
I did fire up the software and loaded a demo line and the menu I think you want is SECTIONS => CLEARANCES => Between Sections... which will bring up a dialog box where you can select the from section and the to section and the weather cases to consider.
HTH
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I have been called "A storehouse of worthless information" many times.