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

1.1 Voltage and Current Relationship

Let I_Lbe the total current drawn from the supply.

So I_L = I_se= I_a

and V = E_b + I_aRa + I_seR_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.