TYPES OF DC MOTORS DC MotorsSeries-WoundMotorFigure 9 Torque-vs-Speed for a Series-Wound MotorSince the armature and field in aseries-wound motor are connectedin series, the armature and fieldcurrents become identical, and thetorque can be expressed as shownin Equation (6-8).(6-8)TKI^{2}_{a}The torque-vs-speed characteristicsof a series-wound motor with aconstant voltage source are shownin Figure 9. As the speeddecreases, the torque for a series-wound motor increases sharply. As load is removed from a series motor, the speed will increasesharply. For these reasons, series-wound motors must have a load connected to prevent damagefrom high speed conditions.Series-WoundMotorApplicationsThe advantage of a series-wound motor is that it develops a large torque and can be operated atlow speed. It is a motor that is well-suited for starting heavy loads; it is often used for industrialcranes and winches where very heavy loads must be moved slowly and lighter loads moved morerapidly.CompoundedMotorThe compounded motor is desirable for a variety of applications because it combines thecharacteristics of a series-wound motor and a shunt-wound motor. The compounded motor hasa greater torque than a shunt motor due to the series field; however, it has a fairly constant speeddue to the shunt field winding. Loads such as presses, shears, and reciprocating machines areoften driven by compounded motors.ES-06 Page 10 Rev. 0