Would we need Alternating Current if superconducting wires existed? The major advantage of Alternating Current is that it can be transmitted to large distances without significant losses, which is not possible in Direct Current.
Had economical superconducting wires existed, DC could be transmitted to any distance without any loss, and DC is much safer compared to AC.
So, I want to know, do we need AC if long distance transmission is no longer a problem because of superconducting wires?
Would DC be better in that case, or we would still need AC?
 A: Ohmic power line losses occur in both DC and AC systems and are always proportional to the RMS value of the current, so your assertion that AC transmission has insignificant losses compared to DC is not correct.
The major advantage of AC power transmission is that the transmitting voltage can be transformed down as needed locally at any point along the line with a simple transformer. This is not possible with DC, which is why it is rarely used for long-distance power transmission. In addition, three-phase AC power transmission directly enables three-phase electric motor technology, which is overwhelmingly preferred in industrial use.
Note that AC power transmission is not inherently more dangerous than DC, and that lossless superconducting lines for long-distance power transmission could be used in either DC or 3-phase AC mode.
A: I’m thinking that you wouldn’t be able to have superconducting wires with AC electricity, as the switching (the direction of flow of electrons moving backwards and forwards) that occurs in AC current would break Cooper pairs. Also, this paper here also seems to suggest that even in superconductors, there still exists a (surface) resistance.
If we could use superconductors in DC power lines, the lack of resistance would mean we can transmit electricity without loss to heat, which would allow for very large current densities - even in thin wires - with zero energy loss. This would reduce demand for the building of more power stations and even reduce the current costs of power. So it seems exceedingly economically viable. The potential benefits of renewable energy devices/environmentally friendly energy in conjunction with this could not be understated.
However maintaining the low  critical temperature needed in the wires would be extremely difficult. At the least it would probably be more expensive, labour and energy intensive to do this, that any benefit would be significantly outweighed by this burden.
But if we could find methods to circumvent these problems, the payoff to humanity would be immeasurable.
A: DC power transmission is more efficient than AC and is used for many long distance lines.  It can also conveniently provide a connection between asynchronous AC systems.  AC is used (especially historically) because of the ease with which voltages and currents can be transformed.   The advent of high-power semiconductor DC-DC converters has made high-voltage DC transmission lines much more practical in recent decades.  Superconducting transmission lines are under serious consideration.
