What occurs in a series direct-current (DC) motor when the load increases?

In a series direct-current (DC) motor, when the load increases, more torque is required to maintain the same speed. As this demand for torque increases, the current flowing through the armature also increases due to the relationship in a series configuration where the field winding is connected in series with the armature.

This increased load results in a decrease in the armature speed as the motor works harder to overcome the resistance posed by the load. The armature speed decreases primarily because, with the increase in load, the motor experiences increased mechanical resistance, requiring more torque and thereby causing the motor to slow down. The interaction between the armature current and the magnetic field produced by the field coil plays a critical role here, as the motor attempts to adjust to the new load conditions.

In summary, an increase in load leads to a decrease in armature speed in a series DC motor, aligning with the principles of motor operation under varying load conditions.