Can anyone explain the use of carbon brushes in a dc motor or turbines?
Any DC motor or generator will need to have a commutator. A commutator is a device used to change the direction of current flow through the motor. The reason a cummotator is needed is because a DC current in a magnetic field can only turn the motor through 180 degrees, after which the force will cause the motor to return to a fixed position. In order to make the force turn the motor the current needs to be changed every 180 degrees so that the force will act in the opposite direction, spinning the motor around. This is achieved using a commutator. The commutator is normally a device which brushes against terminals in the motor. As the motor turns the terminals in contact with the brushes change, and so does the current. AC motors do not need commutators because the direction of the current changes automatically. The disadvantage (or advantage in some situations) is that the motors speed is governed by the frequency of the current.
