# Eee118 Ch10 Final

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1/7/2013 EEE 118: Energy Conversion Dr. Mongkol Konghirun Department of Electrical Engineering King Mongkut’s University of Technology Thonburi Chapter 10 Single-Phase And SpecialPurpose Motors 1 1/7/2013 10.1 The Universal Motor The Universal Motor The universal motor is essentially the series or shunt DC motor. However, it can be operated on a single-phase AC power source. Recall from Chapter 8: τind = KφIA …(8-49) When the polarity of the voltage applied to a shunt or series DC motor
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1/7/20131 EEE 118: Energy Conversion Dr. Mongkol KonghirunDepartment of Electrical EngineeringKing Mongkut’s University of Technology Thonburi Chapter 10 Single-Phase And Special-Purpose Motors  1/7/20132 10.1 The Universal Motor 4 The Universal Motor The universal motor is essentially the series orshunt DC motor. However, it can be operatedon a single-phase AC power source.Recall from Chapter 8: τ ind = K  φ I  A  …(8-49)When the polarity of the voltage applied to ashunt or series DC motor is reversed, bothdirection of field flux ( φ ) and the direction of armature current (I  A  ) reverse, and resultinginduced torque continues in the samedirection as before  1/7/20133 5 Torque-Speed Characteristic The torque-speed characteristic of a universalmotor is different from one of the samemachine operating from DC voltage for tworeasons:1. The armature and field windings have quitelarge reactance (as a function of frequency).So, the voltage drop across these reactancesare large. Thus, the E  A  = K  φω is smaller for agiven input voltage. Then, the motor speed ω is slower for a given I  A  and τ ind .2. The peak voltage of an AC system is √ 2times its RMS value. The magnetic saturationcould occur near the peak current, loweringthe magnetic flux of the motor for a givencurrent. The induced torque is partiallyreduced for a given speed. 6  Applications of UniversalMotors The universal motor has the sharply drooping torque-speedcharacteristic of a DC series motor (E  A  significantlyreduced), so it is not suitable for constant-speedapplications.However, it is compact, light weight and gives moretorque/amp than any other single-phase motor.Typical applications for this motor are vacuum cleaners,drills, similar portable tools, and kitchen appliances.  1/7/20134 7 Speed Control of UniversalMotors Similar to the DC series motor, the speed of universalmotor is increased when the RMS input voltage isincreased. 10.2 Introduction to Single-PhaseInduction Motors
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