Electrical Engineering ⇒ Topic : Principle of d.c motor

PRINCIPLE OF OPERATION

The electric motor is a machine which converts electrical energy into mechanical energy.

The principle of motor action can be stated as follows :

"Whenever current carrying conductor is placed in a magnetic filed, it experiences a force whose direction is given by Fleming's left hand rule."

         Fig. (a) The principle of motor action                                                                          Fig.(b). Motoring operation

The force (F) developed in the conductor is given by the relation,

                         F = BIL newtons 

where B = flux density, T (Wb/m²)

            I = current in conductor, A

            L= exposed length of conductor, m

For a motor :                V = E_b + I_aR_a                          ...known as voltage equation of a motor.,           (1)

For a generator :        E_g = V + I_aR_{a                                                                                                                                           (2)}

where    V = applied voltage (measurable terminal voltage) across the armature

            E_b = back or counter e.m.f. developed in the armature of the motor

            E_g = generated e.m.f. developed in the generator armature

         I_aR_a = armature voltage drop due to a flow of armature current through an armature of a given resistance, Ra.