The carbon brush of the generator is also called the electric brush, because its material is "carbon", so it is often called "carbon brush". The function of the carbon brush is to provide the external power source (usually a DC excitation current) of the generator to the winding (excitation winding) of the rotor through the slip ring on the collector ring. In this way, when the rotor rotates, the DC current flowing in will keep flowing from one end of the rotor, so that the generator rotates in one direction. The carbon brush is connected with the power source to provide electric energy for the rotor.