Student ID: 53703105

Exam: 4033RR - Fractional-horsepower Motors

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Questions 1 to 25: Select the best answer to each question. Note that a question and its answers may be split across a page break, so be sure that you have seen the entire question and all the answers before choosing an answer.

1. The motor best suited for driving a shaft-mounted fan in an air-conditioner which requires a low operating current is the A. shaded-pole motor. B. permanent-split capacitor motor. C. -shifting repulsion motor. D. concentrated-pole .

2. An a-c electrolytic capacitor is placed in the auxiliary-winding circuit of a single-phase motor when A. capacitance should be permanently included in the motor circuit. B. capacitance is needed for the starting period only. C. a leading current is required in the main winding. D. a lagging current is required in the auxiliary winding.

3. At a 40 oz-ft torque and a 700-rpm speed, a motor will produce an output power of approximately 1 A. /10 hp 1 B. /3hp 1 C. /4 hp. 1 D. /2 hp.

4. An auxiliary phase winding is used in a single-phase fractional horsepower motor to A. increase motor speed. B. decrease flux density. C. reverse motor rotation. D. decrease motor heating.

5. What is the effect of applying a lower-than-rated voltage to a fractional-horsepower motor? A. The motor will heat up dangerously. B. The motor will operate satisfactorily at 95% of the rated voltage. C. The motor will operate with increased magnetizing current. D. The motor will start but will not reach the rated speed.

6. The reason for using a laminated core in a universal motor is to A. limit the eddy currents and the iron losses. B. decrease the doc reactance of the field winding. C. maintain a constant level of magnetic flux. D. limit the saturation of the magnetic circuit.

7. The device which responds to the heat developed within the motor is the A. . B. short-circuiter. C. bimetallic protector. D. current-operated relay.

8. If there is only one auxiliary winding in a two-speed capacitor start motor, the motor has to A. reverse the direction of rotation when it changes speed. B. use a speed-selecting control switch and a two-position starting switch. C. start with the low-speed main winding and with the control switch in the low-speed position. D. be stopped whenever the speed is changed.

9. In a repulsion motor, the brush position which causes the to act as a short-circuited secondary is the A. hard-neutral position. B. soft-neutral position. C. minimum sparking position. D. maximum starting-torque position.

10. The arrangement which can NOT be used to control the speed of a universal motor operating from a d- c circuit is A. a mechanical governor. B. a solid-state controller. C. a tapped field winding. D. an adjustable external resistance.

11. If an has two protective housings for capacitors, it is a A. dual-voltage capacitor-strut motor. B. permanent-split capacitor-start motor. C. single-voltage capacitor-start motor. D. capacitor start-and-run motor.

12. Which one of the following statements is true about a two-winding distributed-field universal motor? A. The main and compensating windings are connected in parallel B. The main winding occupies four slots per pole. C. The brushes are shifted off the neutral position. D. The ampere-turns of the compensating and windings oppose each other.

13. In a capacitor-start motor driving a high-inertia load, regeneration can occur during the time when the motor is A. coasting to a stop. B. running at normal speed. C. starting the load. D. accelerating the load.

14. How is a rotating produced during starting in a split-phase motor? A. Brushes are shifted off the hard-neutral position. B. A low resistance coil is placed around a portion of each pole. C. A capacitor is inserted in the auxiliary-winding circuit. D. An auxiliary winding is made with a high ratio of resistance to reactance.

15. Which one of the following doc motors powers a cordless appliance? A. A wound-field shunt motor B. A differentially compound motor C. A cumulatively compound motor D. A permanent- motor

16. A single-phase a-c motor which has both a squirrel-cage winding and regular windings but lacks a short- circuiter is called a A. repulsion-start motor. B. conductively compensated repulsion motor. C. repulsion-induction motor. D. straight repulsion motor.

17. A centrifugal starting switch in a split-phase motor operates on the principle that A. a higher speed changes the shape of a disk to open the switch contacts. B. the voltage induced in the auxiliary winding keeps the switch contacts open. C. a high starting current opens the switch contacts. D. the actuating weights move outward as the motor slows down.

18. The maximum torque produced by a split-phase motor is also called the A. locked-rotor torque. B. full-load torque. C. pull-up torque. D. breakdown torque.

19. Which one of the following statements is true about a dual-voltage capacitor-start motor? A. The auxiliary-winding circuit operates at 115 volts on 115-volt and 230-volt circuits. B. The main windings are connected in series for 115-volt operation. C. The direction of rotation is reversed by interchanging the leads of one main winding. D. The main windings are identical to obtain the same starting torques on 115-volt and 230-volt circuits.

20. A motor which is designed with nonstandard operating characteristics is classified as a A. general-purpose motor. B. nonstandard motor. C. definite-purpose motor. D. special-purpose motor.

21. For a repulsion motor with bmshes set in the neutral position, what type of winding is needed to produce starting torque? A. A starting winding B. An inducing winding C. A capacitor-phase winding D. A squirrel-cage winding

22. The synchronous speed of a four-pole induction motor supplied with 58-Hz a-c power is A. 1740 rpm. B. 1765 rpm. C. 1725 rpm. D. 1750 rpm.

23. The motor characteristic obtained by using a high-resistance rotor in a shaded-pole motor is a A. higher full-load speed. B. greater starting torque. C. more stable operating speed. D. lower slip.

24. The fractional-horsepower induction motor which produces the highest locked-rotor torque is the A. split-phase motor. B. shaded-pole motor. C. permanent-split capacitor motor. D. capacitor-start motor.

25. One characteristic of a typical universal motor is that it A. is usually designed for low-speed operation. B. operates at a constant speed on a-c and doc circuits. C. has a low locked-rotor torque. D. operates at about the same speed on a-c and doc circuits.

End of exam