self-excited generator

A self-excited generator, also known as a dynamo, is a generator whose magnetic field is created by an electric current produced by the generator itself. Introduced in 1867, dynamos convert mechanical energy into electricity. This process relies on electromagnetic induction, where a changing magnetic flux induces an electromotive force in a circuit.1234

The dynamo theory, proposed in the mid-1900s, explains Earth's magnetic field as a self-sustaining dynamo. In this model, fluid motion in Earth's outer core moves liquid iron across a weak magnetic field, generating an electric current. This current, in turn, produces its own magnetic field, strengthening the original field. While the term "dynamo" was once common for generators producing direct current (DC), alternating current (AC) is now standard.53