AC THEORY

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Author:
mike9991
ID:
177503
Filename:
AC THEORY
Updated:
2012-10-14 01:09:01
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ETCO
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AC THEORY
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  1. For what reason is a univerdal motor called universal?
    Because it has the ability to run on either A.C or D.C current
  2. State the typical power rating of universal motors
    Between 3-550 Watts
  3. Explain how change of direction on a universal motor can be acheived?
    Interchange either the armature leads or the field leads
  4. What is housed in  the stator?
    Silicone-Iron laminations with slots containing field coils
  5. How nis the rotor constructed?
    A simple squirrel cage arrangement made up of copper bars and end plates, brazed together
  6. Why are the bars of the rotor skewed?
    To prevent noise
  7. Why is a centrifugal switch needed?
    So that the start winding can be dissconnected as soon as it has served its function
  8. Why is it called the split-phase motor?
    Because the phase needs to be split and displaced
  9. How is phase displacement, to simulate stator field rotation, obtained?
    Two pairs of poles are wired in parallel to the supply and are placed around the circumfrence of a stator housing. One pair of ploes represents the start winding and the other pair represents the run winding. The start winding has fewer poles than the run winding. Therefore the inductive reactance/resistance ratios of the two windings differ, causing a phase displacement between the start winding current and the run winding current
  10. What is the main difference between a split phase motor and a capacitor start motor?
    The two motors are similar in construction but the capacitor start motor has more turns of finer wire in its start winding and has a capacitor in series with its start winding
  11. What is the function of the capacitor in a capacitor start motor?
    To produce a torque that is great enough to start a motor which requires a greater starting torque than that of a normal split phase motor
  12. How can reversal be obtained in a capacitor start motor?
    By changing the connections to either the start winding or the run winding. NOT BOTH
  13. What is the essential constructional differnece between a capacitor start motor and a perminantly split capacitor motor?
    The capacitor start winding has more turns of finer wire than the start winding of a split phase motor
  14. What is the typical power output of a shaded pole motor?
    40watts 
  15. What makes this motor attrative for its use and purpose?
    Its simplicity and robust nature of its construction
  16. What type of rotor does it have?
    The squirrel cage one
  17. Can the shaded pole motor be reversed?
    Only by turning the entire motor around can a reverse feature be obtained
  18. Describe the pole of a shaded pole motor
    Each pole has a shortened coil of one turn placed around about one third of the pole
  19. Why dioes the shaded pole motor run hot around the shaded rings? 
    Because the shaded rings carry particularly high current
  20. What is a motor enclosure?
    A strucural device to protect the motor agianst it environment
  21. Name 4 types of enclosures
    • -Screen protected 
    • -Drip proof
    • -Totally enclosed
    • -Flame proof

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