Alternating current changes its direction and polarity periodically. It became dominant for power transmission at the beginning of the 20th century and is the most frequent method of power transmission worldwide. Alternating current lines can be synchronised, making them suitable for operation in the meshed grid. Alternating current has the advantage that the voltage can be increased or reduced by a transformer. To minimise loss, high voltages are used for transmission over long distances and then reduced to a low voltage close to the end consumer.
With direct current, the electrical current does not change direction. The disadvantage of direct current lines is that they cannot be synchronised without expensive technology and are therefore unsuitable for use in the meshed grid. They are currently used for point-to-point connections and connected to the 50 Hz supply grid through converter stations. These convert the energy to be transmitted from alternating current to direct current and, at the end of the transmission route, back to alternating current so the electricity can be further transmitted in the alternating current grid. These stations require an enormous area. Due to the extremely high investment costs of several hundred million francs and the losses in conversion stations, a direct current line is only economically viable for transmission distances exceeding several hundred kilometres and is therefore only an issue for little Switzerland in connection with the European grid.