Triton College - Engineering Technology ENT104 - Electricity I HW 8 - AC Motors Name __________________________________ Date __________________________________ 1. The rotating part of a typical induction motor is called the ____. A. stator B. rotor C. armature D. capacitor circuit 2. The bars in the squirrel cage rotor are simi- lar to ____. A. the secondary of a transformer B. an open circuit C. a motor protection circuit D. a speed control system 3. Reversing the electrical connections to two of the three motor leads on a three-phase motor will cause the motor to ____. A. overheat B. draw excessive current C. reverse direction of rotation D. double its rpm 4. The speed of the magnetic field of rotation inside the motor stator housing is called ____. A. slip speed B. rpm speed C. rotor speed D. synchronous speed 5. Slip is a calculated figure based on ____. A. rotor speed and synchronous speed B. rotor speed and phase number C. rpm and rotor speed D. rotor speed and frequency 6. Which motor rotor rotates at the same speed as the rotating magnetic field? A. Synchronous. B. Stepping. C. Wound rotor. D. Split phase. 7. Which motor rotates in small controlled increments? A. Synchronous. B. Stepping. C. Wound rotor. D. Split phase. 8. The rotating magnetic field inside the three- phase motor stator housing is based on ____. A. source frequency and number of poles B. source frequency and voltage C. current in the stator windings D. number of poles and resistance 9. The centrifugal switch is connected in series with ____. A. the run winding B. the start winding C. the run and start winding D. only the capacitor 10. A ______ motor would be best for a robotic application that requires an exact degree of movement. A. split phase B. synchronous C. wound rotor D. stepping 11. A coil of wire will produce a phase shift caused by ____. A. capacitance B. induction C. resistance D. frequency 12. When comparing two sine waves that are out of phase with each other ____. A. their peaks occur at different times B. they have different frequencies C. their peak voltage values are different D. All of the answers are correct.
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The rotor is the rotating part of an induction motor; the stator is the stationary part. Show more…
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Problems 1. T/F The difference between the two classifications of PM motors is whether the rotor and field are made of permanent magnets or coils. 2. The speed of a wound armature PM motor is varied by changing the current applied to the ______. a. armature b. stator 3. List three applications of a wound armature PM motor. 4. The speed at which a moving coil motor runs is controlled by varying the ______. a. amplitude of the DC voltage applied to the armature b. width of the pulses applied to the armature 5. List two applications of MCM motors. 6. T/F BDCM motors usually use three-phase power. 7. The direction a BDCM motor turns can be reversed by switching two of the three connections to the ______ of the transistor. a. base b. collector 8. The amount of force required to move the rotor of the BDCM motor away from the held position is called ______. 9. A ______ motor converts electronic digital signals into fixed increments of positional movement. 10. T/F The operation of a variable reluctance motor is based on the ease with which flux lines pass through soft iron. 11. If the stator's magnetic field of the VR stepper motor moves clockwise, the rotor turns ______. a. clockwise b. counterclockwise 12. The stepper motor is typically used in a/n ______ (open, closed) -loop system. 13. A stepper motor that operates at a step angle of 12 degrees will rotate at what RPM if it has a stepping rate of 360? ______ 14. In a variable reluctance motor, if the salient poles are 15 degrees apart and the rotor poles are 20 degrees apart, the step angle is ______ degrees. a. 5 c. 20 b. 15 d. 35 15. The maximum number of steps a stepper motor can make in a second is called ______ ______. 16. The number of degrees a stepper motor turns per step is called ______ ______. 17. The speed at which a stepper motor turns is increased by ______ applied to the stator. a. increasing the stepper rate applied to the stator b. increasing the voltage c. both a and b 18. A stepper motor with twice the step angle of a second stepper motor will turn at ______ the rpm if the stepper rate applied to both is the same. a. half b. twice 19. Microstepping is achieved by ______. a. gradually increasing the voltage applied to one coil while decreasing the voltage at a second coil. b. simultaneously applying simulated sine waves that are out of phase to different coils c. both a and b 20. In an AC servo motor, the phase-shifted voltage is supplied to the ______ winding. a. main b. auxiliary 21. The speed of an AC servo motor is changed by varying the voltage applied to ______. a. the main winding c. none of the above b. the auxiliary winding
Section 4 Specialized Installations 13. A hermetic motor is a motor that is hermetically sealed inside a shell and used to drive a(n) __. A. air compressor B. pulley wheel C. refrigerant compressor D. water pump 14. When selecting a motor controller for use with a hermetic motor, use the __. A. full-load amperage value B. locked-rotor amperage value C. higher of the two values in A and B D. lower of the two values in A and B 15. What is the full-load amperage of the continuous duty, single-phase electric motor in the illustration? 16. How many conductors are used to provide power to the continuous duty, single-phase electric motor in the illustration? 17. What is the locked-rotor amperage of the continuous duty, single-phase electric motor in the illustration? 18. What is the full-load amperage of the continuous duty, three-phase electric motor in the illustration? 19. How many conductors are used to provide power to the continuous duty, three-phase electric motor in the illustration? 20. What is the locked-rotor amperage of the continuous duty, three-phase electric motor in the illustration? 21. The following are causes of overheating in an electric motor, except for __. A. high ambient temperatures B. low voltage at the motor terminals C. motor overloading D. too much ventilation 22. True or False? During periodic motor service, bearings should be lubricated. 23. To ensure that accumulated moisture can drain from a motor, be sure to keep any ___ unobstructed. A. flexible couplings B. pulley wheels C. ventilation louvers D. weep holes
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