Zero resistance transmission lines?
The 'zero resistance transmission lines' are probably bus-ties between physically adjacent busbars, which are only a few metres long and thus have negligible resistance.

For example, in the picture shown below, the "MINE SWITCHBOARD" is an 11kV switchboard with two sections. I would model this as two busbars joined by a zero-impedance bus tie. Note the bus tie panel is only about 800mm wide, so its resistance is truly negligible.





Edit:

On a second read of the question, I see that the lines in question are not zero impedance - they have a zero resistance but nonzero reactance.

I would say that these are modelling an actual reactor element (a.k.a. inductor, line choke). We do use series reactors for fault current limiting in distribution networks. The reactor does have non-zero resistance in real life, but for simulation purposes the resistance is small enough that we usually ignore it.