Direct and alternating voltage - direct and alternating current

Electricity has been an important part of our lives since Werner von Siemens invented the electrodynamo in the 19th century. Whether in industry, traffic, research, medicine or obviously in the household – these days you can find electrically operated machines and appliances everywhere. All these machines and appliances with their electrical wiring are surrounded by electric and magnetic fields.

Electric and magnetic fields

Wires and appliances to which a voltage is applied are surrounded by electric fields. If a current flows, magnetic fields are additionally produced.

A basic distinction is made between direct and alternating voltage or, as the case may be, between direct and alternating current. With alternating voltage, the polarity changes regularly: the negative pole becomes the positive pole and vice versa. When a current flows, the electrons forming the current change their direction of flow accordingly. With direct voltage and current, the polarity and the direction of flow of the electrons are not reversed.

Electricity networks

Many appliances and machines are operated from the public electricity network providing an alternating voltage at a frequency of 50 hertz (Hz). Deutsche Bahn uses its own power grid with a frequency of 16.7 Hz.

The fields generated have the same frequency as the voltages and currents in the relevant networks. These frequencies belong to the lower range of the electromagnetic spectrum. This is why the fields generated are called "low-frequency alternating fields". The fields produced by direct voltages and currents are called static fields. Their frequency is 0 Hz.