Electrical Machines, 2nd Edition

Appendix D

Torques in AC and DC Machine

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

F =Bil  N      (D.1)

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 B_av is given by

The developed torque becomes

For the entire winding, ...