You want low frequency for high efficiency in transmission lines. That's why HVDC is becoming more popular [1]. It wasn't really economical to use DC current fo

You want low frequency for high efficiency in transmission lines. That's why HVDC is becoming more popular [1]. It wasn't really economical to use DC current for a long time because it's more difficult to step up/down the voltage than with AC (you just need a transformer). But power electronics and in particular power semiconductors have advanced so much that HVDC becomes more and more prevalent. As for AC: The higher the frequency the higher the losses, but you can use smaller transformers (without using any fancy power electronics). [1] https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current