Series-Wound Motor:

Because the armature and field in a series-wound motor are connected in series, the armature and field currents become identical, and the torque can be expressed as shown in Equation (6-8).

T = KI²_a                                                                             (6-8)

The torque-vs-speed features of a series-wound motor along with a constant voltage source are display in Figure. As the speed decreases, the torque for a series-

Figure: Torque-vs-Speed for a Series-Wound Motor

wound motor increases sharply.  As load is removed from a series motor, the speed will rise sharply.  To these reasons, series-wound motors must have a load linked to avoid damage from high speed conditions.