cross section of a high power electric car charging cable. the electric current is so high that the copper wires would overheat, but coolant flows through small tubes in the center of each wire.
@tubetime Generators often do the same with stator windings: they are basically pipes and distilled water is passed through them. I'm not entirely sure why conductivity of that water matters (after all its share of current will be very small, and it being AC would seem to obviate worries about corrosion). It seems that here the internal pipe is insulated?
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Ah, it's at least partially about leaks, which might create a water path between stator winding and ground. See e.g. https://www.nrc.gov/docs/ML0306/ML030650924.pdf
