Question

Why is it that AC current can be transported over long distances whereas dc current can't be done so?

Answer 1

What's good for long-distance power transmission is high voltages. The higher the voltage, the lower the resistive losses in the cable. That's why mains power is transmitted at many hundreds of thousands of volts, and is only stepped down to the 110V or 230V that you're used to when it is near your building.

AC is much easier (therefore cheaper) to step up and down in voltage than DC using a transformer, and can be done more efficiently (typcially, currently) than the much more expensive and complex DC step-up/step-down systems. That is why AC is preferred for mains power transmission over DC.