When a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force. If a conductor of length ‘l’ metres carrying a current ‘i’ ampere is placed in a magnetic field having flux density B Wb/m2, the mechanical force (F) exerted on it is given by
Let the diameter of the rotor be D. The force acts at a radial distance of metres. The torque per conductor is expressed by
The average flux density Bav is given by
The developed torque becomes
For the entire winding, the torque developed is the summation of the torques for the individual conductors or coil sides. This torque developed due to electromagnetic action is known as electromagnetic torque (Te).
where Z is the total number of conductors.
For a DC motor, the current per conductor is given by
where Ia is the armature current and A is the number of parallel paths.
From Equation (D.5), we have
Equation (D.6) represents the torque developed by the armature of a DC motor.
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