This invention relates to a transformer containing an insulated power cable including a multi-strand cable of a plurality of bundles of uninsulated wires, and electrical insulation sheathing the cable, the electrical insulation having a thickness of from 0.0625 to 0.5 inches (0.16 to 1.3 centimeters) and containing a plurality of layers of spirally-wrapped, creped tape, the tape being including at least 50 percent by weight of an aramid material, the tape having a density of from 0.1 to 0.5 grams per cubic centimeter prior to being creped.