Electrical Engineering ⇒ Topic : Torque developed in a motor

TORQUE DEVELOPED IN A MOTOR

The expression for the torque developed by the motor armature may be deduced as follows :

Let T_a be the torque developed in N-m by the motor armature running at N r.p.m.

Power developed = work done per second

                             =  T_a X 2πN Watts                 ............  (i)

Electrical equivalent of mechanical power developed by the armature also

                             =   E_b I_{a                                               ................  (ii)}

Equating (i) and (ii), we get

                                                    .............  (iii)

Note. From the above equation for torque, we find that T ∝ ΦI_a

Then

In the case of shunt motors, (Φ) is practically constant,

hence                                 T ∝  I_a

In the case of series motors, (Φ) is proportional to I_a (before saturation because field windings carry full armature current),

                                          T ∝  l²_a