Direct voltage or alternating voltage?

Alternating voltage suffers more losses when transported over long distances than direct voltage. This is because a high-voltage line has small inductance and capacitance to ground. Over the inductance, an alternating current loses voltage. In addition, an AC voltage across a capacitance leads to a leakage current to ground. As the concatenation of inductances and capacitances becomes longer, the losses also increase. With DC voltage, inductance and capacitance play no role and only the ohmic losses remain. These can be lowered by choosing a higher voltage. The use of direct current has a future but often alternating current remains more convenient. It is interesting to realize that electricity once started with direct current.

Alternating voltage suffers more losses when transported over long distances than direct voltage. This is because a high-voltage line has small inductance and capacitance to ground. Over the inductance, an alternating current loses voltage. In addition, an AC voltage across a capacitance leads to a leakage current to ground. As the concatenation of inductances and capacitances becomes longer, the losses also increase. With DC voltage, inductance and capacitance play no role and only the ohmic losses remain. These can be lowered by choosing a higher voltage. The use of direct current has a future but often alternating current remains more convenient. It is interesting to realize that electricity once started with direct current.

Alternating voltage and alternating current are surprisingly efficient. Yet at higher voltages, you see increasing interest in direct voltage. The background to this is the following: with alternating current you need three phases to carry electricity and with direct current you only need two wires. You could even do with one wire if you use the earth as a return conductor. So one saves directly on aluminum (the material of high-voltage power lines). Moreover, if there are only two wires hanging in a mast, then the high-voltage pylons can be made less sturdy. But we pay a price for that, because AC voltage must be converted to DC voltage and at the end of the line DC voltage back to AC voltage. This is done with converter stations and they are pricey. That means there is a tipping point, and it is currently at 100 kilometers at sea and 800 kilometers on land. The implementation of new high-voltage power lines in China is in many cases in direct voltage. That’s all proven technology. It can be ordered from ABB, Siemens, Alstom and various Japanese suppliers and then it will be delivered turn-key.

So more and more direct voltage is coming into high voltage. And more and more equipment in our homes also operates on direct current. Would it be wise to make the entire power grid DC then? Alternating voltage also has obvious advantages. This is because you can interrupt an alternating current with a switch but not a direct current. That’s one of the problems. But even if you had a dc switch, a transition to an all dc grid gives too few benefits . Just because home electronics are powered by direct current does not mean that the entire household runs on direct current. Because if you literally want to get something to spin, then AC voltage is a lot more convenient than DC voltage. Before the electric age, we had the steam age but still many things have to run – as much as 60 percent of electric energy is used for drives. Not for nothing is alternating current also called three-phase current.