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Thread: 309A exam prep. question

  1. #1

    Default 309A exam prep. question

    Here's the 309A prep question and answer:
    1. A four-pole 60hz SCIM has a full load speed of 1770 RPM at full load. Calculate the % slip of the motor at full-load.
    Answer: 1.67%
    Can someone explain to me how to figure this out because I have no idea.
    Thanks.

  2. #2
    Join Date
    Dec 2003
    Location
    Kent, WA
    Posts
    8,431

    Default

    60 cycles per second = 120 peaks per second if you look at the plus and minus voltage cycles. 120 cycles per second * 60 seconds = 7200 RPM if the motor had one pole.

    7200 / 4 poles = 1800 RPM calculated RPM.

    Actual RPM was 1770 / 1800 = 98.333% of theoretical speed. So slip is 100% - 98.33% = 1.67%.
    Mark
    Kent, WA

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