3. Reconnecting Induction Motors

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Penn Foster College *

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0086122RR

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Mechanical Engineering

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Dec 6, 2023

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student id: 55385260 exam: 6585RR - Reconnecting Induction Motors When you have completed your exam and reviewed your answers, click Submit Exam . Answers will not be recorded until you hit Submit Exam . If you need to exit before completing the exam, click Cancel Exam . 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. Which one of the following leads on a dual -voltage motor serves as a motor terminal? A. T2 B. T5 C. T7 D. T4 2. A 12 -pole 575- volt 60 -Hz motor has a chord factor o{ 0.892. If the motor is reconnected as a 16- pole motor with a chord factor of 0.968, the operating voltage due to changes in the chord factor and in the speed is A. 682 volts B. 468 volts C. 780 volts D. 398 volts 3. If a two-phase 230-volt motor is changed to a three-phase Y-connected motor, the new motor voltage is A. 184 volts B. 398 volts C. 288 volts D. 325 volts 4. If a 460- volt Y -connected three-phase motor is reconnected inc., the new line voltage should be A. 265 volts. B. 208 volts. C. 797 volts. D. 575 volts. 5. By a quick estimate and without the use of a form?? the full-load current in a three-phase 230- volt 10 -hp induction motor is A. 6 amp. B. 24 amp. C. 12 amp. D. 48 amp.

6. The reconnection that can be made for a three-phase 10-pole 230-volt motor connected in 2- parallel A. 3- parallel Y. B. 4- parallel △ C. 4- parallel Y. D. 5- parallel △ 7. Chorded windings are used in induction motors because they A. have better electrical characteristics. B. are made with smaller wire and are therefore cheaper. C. are made with less wire and are therefore cheaper. D. have better mechanical characteristics. 8. If you stub a motor winding, you A. reinforce the insulation. B. cut the leads off. C. make the coils shorter. D. form phase - pole groups. 9. Which one of the following motor characteristics is calculated to determine whether the shaft strength is satisfactory? A. Belt pull B. Torque C. Speed D. Bearing size 10. When a motor is reconnected from 6 poles to 4 poles with no other changes, the magnetic flux density of the stator A. decreases in the core and the teeth. B. increases in the core and decreases in the teeth. C. increases in the core and the teeth. D. decreases in the core and increases in the teeth. 11. Which one of the following number of parallels CANNOT be used in an 18-pole motor? A. 3 B. 5 C. 2 D. 4 12. If a 60-Hz three-phase motor has a nameplate full-load speed of 500 rpm, the number of pole-phase groups in the motor is A. 24. B. 32.

C. 14. D. 42. 13. The voltage in a 460-volt motor is changed to 425 volts. If the original torque was 125 lb-ft, the new torque is A. 135 lb - ft. B. 117 lb - ft. C. 115 lb - ft. D. 107 lb - ft. 14. Which one of the following pitches is the minimum recommended pitch for a 24-pole motor with 360 slots? A. 10 slots B. 15 slots C. 8 slots D. 12 slots 15. The effect of connecting a 50-Hz motor to a 60- Hz circuit and increasing the motor voltage by 6 / 5 is that the motor A. speed will remain constant. B. output power will increase. C. torque will decrease. D. stator current will increase. 16. If the arrows indicating the instantaneous direction of current are properly drawn on a position diagram for a three-phase motor, how will the arrows point? A. All clockwise B. Alternately clockwise and counterclockwise C. All counterclockwise D. Alternately clockwise and counterclockwise, in groups of two 17. If a 575-volt three- phase motor originally connected in 3 - parallel △ is reconnected in 5- parallel Y, the new voltage is A. 747 volts. B. 598 volts. C. 794 volts. D. 501 volts. 18. If a 10- pole 50 -Hz motor should operate at the same speed on a 60-Hz circuit, the motor should be reconnected to produce A. 14 poles. B. 8 poles. C. 12 poles.

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D. 16 poles. 19. A 10 -pole 230-volt three-phase motor has 120 slots and a coil pitch of 8 slot.s. If the motor is reconnected as a 12-pole motor, what is the new operating voltage, assuming that only the change of the chord factor is considered? A. 240 volts B. 261 volts C. 212 volts D. 250 volts 20. A three-phase 575-volt motor requires a voltage of 991 volts after being reconnected to a 4- parallel Y connection. Instead of applying this odd-voltage, however, the customer prefers to use 575 volts. Which one of the following coil -group connections makes operation on 575 volts possible? A. 3- parallel Y B. 2- parallel △ C. 4- parallel △ D. 2- parallel Y 21. A 230 - volt 60 -Hz three-phase △ -connected two-speed induction motor has a chord factor of 0.9 and 400 turns in series per phase. When the motor is running at its slow speed, the flux per pole is A. 502,000 lines of force. B. 319,000 lines of force. C. 290,000 lines of force. D. 553,000 lines of force. 22. A 100 -hp 460-volt three-phase induction motor has a power factor of 90% and an efficiency of 0.92. The full-load terminal current, found by the proper formula, is A. 100 amp. B. 120 amp. C. 130 amp. D. 113 amp. 23. The arrow-check method of determining connections of pole-phase coil groups assumes that A. only one current flows toward the star point. B. all current.s flow toward the terminals. C. only one current flows away from the star point. D. all current.s flow toward the star point. 24. The total flux per pole of a reconnected motor is 900,000 lines of force. If the cross-sectional area of the laminated core is 6 sq in. and the cross-sectional area of the teeth per pole is 14 sq in., the flux density in the teeth is approximately A. 98,300 lines. B. 101,000 lines.

End of exam C. 105,000 lines. D. 120,000 lines. 25. Which one of the following voltage changes is possible with two -phase motors? A. Reconnection from △ to Y B. Reconnection from Y to △ C. Reconnection of pole - phase groups in series or parallel D. Reconnection of coil groups and phase windings