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79 Matching questions

  1. What are two ways that the direction of rotation of a DC motor can be reversed?
  2. Torque is directly proportional to the product of ________ and _______________.
  3. List the factors that cause a reduction in terminal voltage with increasing load.
  4. What is armature reaction?
  5. In a self-excited generator, voltage build-up requires the presence of ___________?
  6. What is the electrical function of the commutator?
  7. The terminal voltage of a shunt generator is controlled by?
  8. Why would it not be practical to control the output of a series generator with a field rheostat?
  9. Line drop can be compensated for by using a generator that is __________.
  10. Heat produced by current flowing through the armature and field coils is called?
  11. The speed at which a DC motor operates without speed control devices is called _____________?
  12. What are two basic types of armature windings?
  13. Describe how the voltage characteristic of series field coils could be useful.
  14. Define efficiency.
  15. At standstill, the counter emf of a motor is __?
  16. The difference between applied voltage and counter emf is called _____________?
  17. Describe the conditions that must be satisfied to obtain the desired performance when connecting a generator.
  18. What factors that influence generated voltage can be varied in an operating generator?
  19. The variation in motor speed with load is called _____________________?
  20. Why does increasing the resistance in the field circuit of a DC motor cause the speed to increase?
  21. The condition under which the magnetic flux of the series and shunt fields oppose each other is called.
  22. To operate a motor below base speed, it is necessary to decrease _____________.
  23. What device in the shunt field circuit is used to control generator voltage?
  24. Suitable brush pressure is usually between _________ and _________ psi.
  25. In a series generator, why does the terminal voltage rise with increasing load?
  26. What are two adverse effects of armature reaction if uncorrected?
  27. A generator characteristic curve shows the effect of _______________ on _______________.
  28. The emf induced in armature conductors as they cut the magnetic field is called _____________.
  29. What is the motor effect principle of magnetism?
  30. What are the common materials used in making brushes?
  31. What is the main difference in the construction of a DC generator and a DC motor?
  32. In a motor, power is proportional to ______________ and ____________.
  33. Grease nipples in the end shields indicate that the machine contains which type of bearings?
  34. Which field windings are made of a low number of turns of large gauge wire?
  35. When the speed of a motor decreases due to an increase in mechanical load, the counter emf will _________.
  36. How are interpole coils connected?
  37. What determines the amount of current that flows through an armature?
  38. The effects of armature reaction can also be minimized by placing windings called _____________ in the main pole faces.
  39. Why are interpoles connected in series with the armature?
  40. The most common solution for minimizing the effects of armature reaction involves the use of _________?
  41. The value of field resistance that will limit field current to a value insufficient for voltage build-up is called _______________?
  42. What are small generators that use permanent magnets for field excitation are called?
  43. A locked rotor usually means that the motor will ________________.
  44. Why is a locked rotor condition undesirable?
  45. Appropriate residual magnetism can be established on the field poles by a process commonly called __________ the _____?
  46. What is the effect on generated voltage if the speed of the prime mover is decreased by one third?
  47. What is the difference between separately excited and self-excited fields?
  48. List the two ways in which field coils are connected in self-excited generators.
  49. How is the starting current limited to a safe value in large DC motors?
  50. The rotating part of a DC generator is called the ___________?
  51. What are three types of power loss in a generator?
  52. How does the operation of the armature differ between a DC generator and a DC motor?
  53. With respect to long vs. short shunt connections, what is a general rule?
  54. Rotational losses include ___________ and ____________.
  55. How is the effect of eddy currents minimized in the construction of DC machines?
  56. What are the 5 key factors that influence generated voltage?
  57. Effective armature voltage is the product of __________ and __________.
  58. What should be done at generator start-up to avoid the problem associated with critical field resistance?
  59. What are two effects of armature reaction on the operation of a generator?
  60. Which armature winding is used in high current, low voltage applications?
  61. What is the function of the field poles?
  62. Why is the no-load voltage of a series generator extremely low?
  63. A practical method of operating below base speed involves controlling ____________.
  64. A compound generator that has a relatively constant terminal voltage characteristic is referred to as __________.
  65. Interpole coils consist of?
  66. At start-up, the current drawn by a DC motor is limited only by __________________.
  67. Voltage build-up occurs until the generator reaches its ___________?
  68. A compound generator contains what type of field?
  69. The condition under which the series field adds to the shunt field is called.
  70. Describe the difference between long shun and short shunt connections.
  71. The motion of armature conductors cutting a field, results in an induced emf that _____________ the applied emf.
  72. Is the series generator a practical machine?
  73. What is Fleming's right-hand motor rule used to determine?
  74. What would happen if an increase in mechanical load exceeded the ability of the motor to develop additional torque?
  75. List the letters that are used in the NEMA system to identify the armature, shunt and series fields.
  76. The counter emf of a motor is proportional to ______________ and ______________.
  77. What is torque?
  78. A reduction in counter emf causes armature current to _____________.
  79. DC machines use _________ or _________ bearings.
  1. a Counter emf.
  2. b The generated voltage is reduced by one third.
  3. c A reduction in terminal voltage with an increasing load. Impaired commutation.
  4. d Field rheostats should be set to their minimum ohmic value.
  5. e Field poles provide the necessary magnetic field.
  6. f Series windings.
  7. g Flashing the field.
  8. h Interpole coils are connected in series with the armature.
  9. i Torque is a twisting or turning force that is capable of producing rotation about an axis.
  10. j Connected load on terminal voltage.
  11. k Whenever a conductor carries current in the presence of a magnetic field, a force will act on the conductor at right angles to the field.
  12. l Lap and Wave.
  13. m The persistence of high starting current may damage the motor.
  14. n Differential compound.
  15. o Armature current.
  16. p Armature current, armature resistance.
  17. q Series and shunt (parallel).
  18. r No-load terminal voltage.
  19. s As armature current increase, the strength of the series field increase.
  20. t Flux per pole ( excitation and rotational speed.
  21. u The field coils must be properly connected with respect to the armature and to each other.
  22. v Reverse the connection of the armature leads. Reverse the connection of both the series and shunt field leads.
  23. w Sleeve or ball bearings.
  24. x Compensating windings.
  25. y The impedance of the connected load.
  26. z Toque and speed.
  27. aa The motor would stall.
  28. ab The rising voltage characteristic is used to offset the decrease in terminal voltage associated with shunt field excitation in a compound generator.
  29. ac The direction of force acting on a conductor.
  30. ad Speed regulation.
  31. ae The type of enclosure.
    generator (open frame) motor (fully enclosed).
  32. af Efficiency is the ratio of power out to power in.
  33. ag Residual magnetism.
  34. ah A small number of turns of large gauge wire.
  35. ai Lap windings are used in high current, low voltage applications.
    Wave windings are used for low current, high voltage applications.
  36. aj Critical field resistance.
  37. ak Armature resistance.
  38. al Both series and shunt.
  39. am Number of poles, flux per pole, rotational speed, number of armature paths, number of active armature conductors.
  40. an The voltage applied to the armature.
  41. ao A rheostat in the field circuit. (field rheostat)
  42. ap No.
  43. aq Increase.
  44. ar Effective voltage.
  45. as Resistance is placed in series with the armature.
  46. at In a generator, the armature is a source of emf. In a motor, the armature is a load.
  47. au Over-compound.
  48. av Fail to start.
  49. aw Decrease.
  50. ax Without a load the circuit is an open circuit so no current flows through the series field coils.
  51. ay Connect the shunt field across the source of emf.
  52. az Opposes.
  53. ba Armature reaction is a distortion of the main field flux caused by current flowing in armature conductors.
  54. bb Weakening of the main field, Exvessive brush sparking.
  55. bc Magnetos.
  56. bd Armature.
  57. be The current for separately excited fields is obtained from a source external to the machine.
  58. bf The rheostat would have to carry the high armature current resulting in high wattage losses.
  59. bg Mechanical, electrical, magnetic.
  60. bh Open faced ball bearings.
  61. bi Interpoles.
  62. bj 0
  63. bk Flux, speed.
  64. bl Flat-compound.
  65. bm Base speed.
  66. bn One and two psi.
  67. bo Copper losses.
  68. bp So that the strength of the interpole matches the strength of the armature field.
  69. bq Flux, armature current.
  70. br IR drop of the armature, armature reaction and loss of field current due to reduction in generated voltage.
  71. bs Cumulative compound.
  72. bt The increase in armature current )due to a decrease in counter emf) is greater than the decrease in excitation.
  73. bu Armature = A; Shunt field = F; Series field = S
  74. bv Field rheostat.
  75. bw In long shunt, the shunt field is connected across the line. In short shunt, the shunt field is connected across the armature.
  76. bx The commutator maintains the current in one direction to the external circuit.
  77. by Carbon, graphite, electro-graphite, and copper graphite.
  78. bz Bearing friction and windage.
  79. ca By laminating the core materials.