Rotating Machinery and Maintenance

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Rotating Machinery and Maintenance
2013-02-01 13:35:02
EM Study Guide

Chapter 7 EM rating book
Show Answers:

  1. The main objectives of shipboard preventative maintenance are to prevent all EXCEPT which of the following situations?
    Generators from being synchronized out of phase
  2. The accumulation of dirt, moisture, and oil in generator and motor ventilation ducts causes local or general overheating for what reason?
    The resistance to the dissipation of heat is increased
  3. If you need to find the detailed procedures for cleaning electrical machinery, you should refer to what chapter of the NSTM?
  4. You are blowing dust from a 75-KW generator using compressed air. What means should you use to remove the dust-laden air from the generator?
    Compressed air pressure of less than 30 psi 
  5. Which of the following is NOT a cleaning solvent you should use when cleaning electrical equipment?
  6. What type of bearing is designed to support loads resulting from forces that are applied perpendicular to the shaft?
  7. In motor construction, what factor determines whether a thrust or radial bearing is installed?
    Whether the motor is mounted vertically or horizontally
  8. In operating machinery, you should suspect malfunctioning ball bearings if which of the following g symptoms occurs?
    1. A loss of speed 2. Arcing brushes 3. A high temperature 4. All of the above
  9. You are starting a motor. You can expect serious bearing problems if high temperatures are reached within what specified amount of operating time?
    10 to 15 minutes
  10. When grease cups for a motor aren’t used to grease bearings, where should they be kept?
    In the custody of the responsible maintenance personnel
  11. Of the following motors, which one can you grease without disassembling the bearing housing?
    A vertically mounted motor 
  12. In the absence of other instructions, at what specified level should you maintain the oil in an oil-lubricated, ball-bearing motor housing?
    Almost level with the bearing inner ring at the lowest point
  13. To prevent damage to a bearing that you are pulling, you should place the bearing puller on the shaft and what other assembly?
    The inner race
  14. When cutting a seized bearing from a shaft, you should be careful to cut only 3/4 of the way through the inner ring. What is the reason for this precaution?
    To prevent damaging the shaft
  15. When bearings are replaced on a shaft, the pressure should be applied to which of the following locations?
     The bearing inner race ( I think)
  16. You are using the infrared method for mounting a motor bearing. The bearing temperature should NOT exceed which of the following temperatures?
    203°F ±10°
  17. Because of grease deterioration or contamination, which of the following methods of mounting bearings is undesirable?
    The hot-oil method 
  18. Which of the following types of bearings are used on large propulsion generators and motors?
  19. The sleeve bearings of a motor overheat. As a watch stander, what action should you take?
    Stop the motor immediately after securing the load 3. Secure the load and let the motor run until the bearing cools
  20. What type of bearing is designed to support loads resulting from forces that are applied perpendicular to the shaft?
  21. What bearing is used when the load is completely axial?
  22. What type of bearing is used in an application where there are radial and thrust loads?
  23. What bearing types are examples of antifriction bearings?
    Ball and Roller
  24. Which of the following factors determines the grade of brush used in a motor or generator?
    1. The time in service 2. The size of the motor or generator 3. The load and speed of the motor or generator 4. All of the above
  25. At what point should you install new brushes in a generator or motor?
    When the brushes are worn to within 1/8 inch of the metallic parts
  26. What method should you use to calculate brush pressure?
    Divide the spring pressure by the brush contact area
  27. When seating a brush, you should use sandpaper and what other equipment?
    a brush seater
  28. When seating a brush, you should place the sandpaper between the brush and the commutator with the rough side toward (a) what component and (b) pull in what direction?
    (a) The brush (b) in the direction of rotation
  29. Of the sequences shown below select the proper one for seating brushes.
    Use No.1 sandpaper, Use No.0 sandpaper, Vacuum carbon, use brush seater at heel of brush, vacuum white powder
  30. On propulsion and magnetic minesweeping equipment, only one grade of brush is permitted. What means is used to determine the grade?
    The manufacturer
  31. If you do not have the applicable technical manual, what tension should be placed on the brushes of integral kilowatt generators?
    2 to 2 1/2 psi
  32. Brush holders should be no more than what (a) maximum distance nor what (b) minimum distance from the commutator of a motor or generator?
    (a) 1/8 inch (b) 1/16 inch
  33. To complete the job of seating the motor brushes, you should perform which of the following steps?
    Touch the seater to the commutator for 1 or 2 seconds, vacuum the dust that results, and clean the commutator
  34. You are trying to locate the best position for commutation using the reverse rotation method. Which of the following is the correct procedure for you to follow?
    Use full load, measure the speed, reverse the direction of rotation, and adjust the reversing the rotation and adjusting the brushes until the rated speed is achieved
  35. After 2 weeks of operation, a commutator develops a bluish-colored surface. What is the cause?
    improper commutation
  36. What is the maximum distance an armature commutator may be out of round?
    0.002 inch
  37. Which of the following methods should you use to correct an out-of-round commutator?
    Machine stoning
  38. To true a commutator in place, you should use which of the following methods?
    Hand- or machine-stoning
  39. The good undercutting shown is best described by which of the following statements?
    The mica is cut low and square between the copper segments or The mica is cut low and square between the commutator risers (not sure)
  40. A commutator is being hand stoned. At what recommended speed should the armature be rotated?
    At or slightly under the rated speed 
  41. You need to season commutators in minimum time. To do this, you should start with 25% of full load operating for (a) what specified number of hours and then increasing the load to operate at (b) what percentage per hour until full load is reached?
    (a) 3 (b) 15%/1
  42. When a large rotor is lifted by rope slings, which of the following components should be protected from the slings?
    The bearing journals
  43. In a wound-ac rotor, reduced torque, excessive vibration, sparking at the brushes, and an uneven collector ring are indications of what electrical malfunction?
    A shorted rotor coil
  44. Of the sequences shown below, select the one for testing a damaged stator
    test for grounds, continuity test, mechanical dificulties and visually inspection of stator
  45. When testing a three-phase, wye-connected winding for shorted pole-phase groups, what method should you use?
    Apply low-voltage dc between each phase lead and the midpoint of the connected phases
  46. What is the indication for a shorted pole-phase group?
    No deflection of the compass needle
  47. The balanced current test is performed on three-phase ac windings to locate what type of motor malfunction?
    Shorted phases
  48. You are testing a three-phase, delta-connected winding for a shorted phase. What procedure should you follow?
    Open each delta connection and send low-voltage ac through each phase separately
  49. You are using an ohmmeter to test a three-phase, wye-connected winding for an open circuit. You get a low reading when the ohmmeter leads are on terminals A and B, a high reading when the leads are on B and C, and another high reading when the leads are on A and C. These readings indicate that there is an open in what phase?
  50. When testing a three-phase, ac, delta-connected winding, you open each of the connected phases and pass low-voltage dc through all phases in series.
  51. Blue sparks that pass around the armature of a running machine indicate an open armature coil. The sparking occurs because, as the segment to which the open coil is attached passes under a brush, the brush is performing which of the following actions?
    1. Closing and opening a circuit 2. Burning the coil insulation 3. Shorting out the coil 4. Grounding the coil
  52. After you have rewound and baked an armature rated at 500 volts, what is the lowest megohm reading allowed? (NOTE: This reading is taken before a high-potential test.)
    1. 1.0 megohm 2. 2.0 megohms 3. 200.0 megohms 4. 400.0 megohms

    i think
  53. A pole pitch is best described by which of the following phrases?
    The distance between the centers of two adjacent poles
  54. What is meant by the term progressive lap winding?
    The winding is connected to adjacent segments, and the connections progress in a clockwise direction
  55. What is the purpose of the bar-to-bar test in an armature stripping procedure?
    To determine the type of winding
  56. The milliammeter reading decreases when the probe at segment 2 is moved successively from segments 2 through 11 and then increases from 11 through 21. What type of winding is indicated?
    Simplex lap
  57. The milliammeter decreases and then increases two times when the probe at segment 2 is moved successively to each segment around the commutator. What type of winding is indicated?
    Four-pole wave
  58. You are testing a commutator using the bar-to-bar method. What equipment should you use?
    A 6-volt battery and milliammeter
  59. The tool identified as number 5 is used for which of the following functions?

    To undercut the commutator
  60. What means are used to classify electrical insulating materials?
    Their temperature indexes
  61. What is the upper temperature rating of class A insulation that has been immersed in dielectric?
  62. To prevent the pocketing of varnish when varnishing a stator, you should rotate the armature during which of the following steps?
  63. What method should you use to conduct an ac high-potential test on a newly rewound armature?
    Short-circuit the commutator segments with several turns of bare wire and apply the test voltage across the common connection and the grounded armature shaft
  64. Before assembling the coils in an armature, what type of insulation should you place in the coil slots?
    Polyamide paper
  65. To prevent centrifugal force from throwing the coils outward, when should you place the banding wire on the armature?
    Before baking
  66. What, if anything, is the difference between shunt and series field coils?
    Shunt field coils are made of many turns of fine wire, and series field coils are made of fewer turns of heavy wire
  67. In what direction does current flow in group 10 of phase A?
  68. When you have completed winding a coil, which of the following devices should you use to make a polarity check?
    A compass
  69. DC motors are usually reversed by a change in the direction of current flow through the armature for which of the following reasons?
    Only one element is involved 
  70. What means should you use to reverse the direction of rotation of a three-phase motor?
    Reverse two motor leads only 
  71. Usually, what is the cause of single-phase motor failure?
    Starting winding failure
  72. If the motor is running on 110 volts, and you want to run it on 220 volts, you should connect the windings in what way?
    Connect the run windings in series
  73. The running and starting windings are placed in the stator of a single-phase motor in which of the following ways?
    The running winding is placed in the bottom of the slots, and the starting winding is placed on top of the running winding