Electrical machines can be divided into two types depending upon the type of current they are supplied, these are ac machines and dc machines. Now in case of dc machines the two type of machines, which are used widely are dc generators and dc motors. In every rotating electrical machine there are two parts, stator and rotor. For dc motors the field wielding is connected with the stator and the armature winding is connected with the rotor part of the motor.
dc shunt motor
For dc motor there is a field connected in parallel or series with the dc motor. Depending on this there are three types of dc motor series motor (where field is connected in series with the motor), shunt motor (where the field is in parallel with the motor) another type of motor is compound motor where series and shunt field both are present in the motor.
Now the main working principle of any dc motor is mainly due to electromagnetic phenomenon, the above mentioned field acts as permanent magnet. The current through the field I flows which marks it a permanent magnet. Now V terminal applied to the motor. We know that where current flows through circuit and that circuit is present inside a magnetic field then there is a torque produced, which is directed towards depending upon the face of the permanent magnets. Same case goes on with dc motors. When V is applied the rotor starts to rotate and then after a while back emf is produced due to the generation action which is in opposite direction with the supplied voltage. The equation of a dc motor can be written as Vt = Ea + Ia.ra.
Here Vt = terminal voltage.
A general and very basic idea about the working principle of dc motor is given above.
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