DC Motors TYPES OF DC MOTORSFigure 7a shows an externally-excited DC motor. This type of DC motor isconstructed such that the field is not connected to the armature. This type of DCmotor is not normally used.Figure 7b shows a shunt DC motor. The motor is called a "shunt" motor becausethe field is in parallel, or "shunts" the armature.Figure 7c shows a series DC motor. The motor field windings for a series motorare in series with the armature.Figures 7d and 7e show a compounded DC motor. A compounded DC motor isconstructed so that it contains both a shunt and a series field. Figure 7d is calleda "cumulatively-compounded" DC motor because the shunt and series fields areaiding one another. Figure 7e is called a "differentially-compounded" DC motorbecause the shunt and series field oppose one another.S h u n t - W o u n d M o t o rFigure 8 Torque-vs-Speed for a Shunt-Wound DC MotorOperationThe speed-torque relationship for atypical shunt-wound motor isshown in Figure 8.A shunt-wound DC motor has adecreasing torque when speedincreases. The decreasing torque-vs-speed is caused by the armatureresistancevoltage drop andarmature reaction. At a value ofspeed near 2.5 times the ratedspeed, armature reaction becomesexcessive, causing a rapid decreasein field flux, and a rapid decline intorque until a stall condition is reached.Shunt-WoundMotorApplicationsThe characteristics of a shunt-wound motor give it very good speed regulation, and it is classifiedas a constant speed motor, even though the speed does slightly decrease as load is increased.Shunt-wound motors are used in industrial and automotive applications where precise control ofspeed and torque are required.Rev. 0 Page 9 ES-06
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