D.C. Series Motor

In this type of motor, the series field winding is connected in series with the armature and the supply, as shown in the Fig. 1.

Fig. 1  D.C. series motor

Let R_se be the resistance of the series field winding. The value of R_se is very small and it is made of small number of turns having large cross-sectional area.

1.1 Voltage and Current Relationship

Let I_L be the total current drawn from the supply.

So         I_L = I_se = I_a

and        V = E_b  +  I_a Ra + I_se R_se + V_brush

V = E_b  + Ia (Ra + R_se) + V_brush

Supply voltage has to overcome the drop across series field winding in addition to E_b  and drop across armature winding.

Note : In series motor, entire armature current is passing through the series field winding. So flux produced is proportional to the armature current.