synchrounous motors

Discussion in 'Homework Help' started by amilton542, Feb 8, 2011.

  1. amilton542

    Thread Starter Active Member

    Nov 13, 2010
    when the rotor synchronizes without DC excitation it states that the rotor will slip a pole and the magnetic field of the rotor will oppose the magnetic field of the stator.
    what do they mean by the rotor slips a pole and opposes the stator field? the rotor is constantley rotating past the poles how can it miss out a pole, do they mean the rotation will be quicker than the synchrounous speed so the rotor will generate a CEMF into the field windings which opposes the stator field?
    But when two fields are opposing each other it also sates that there will be a current surge, why are the opposing fields hungry for more juice?
    Last edited: Feb 8, 2011
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    Perhaps "they" are referring to the fact that under pre-synchronous conditions the rotor field is always slipping behind the stator field. Under these conditions there are pulsations in the resultant rotor torque. Synchronous "pull-into-step" occurs when the North & South poles of the stator and rotor fields are aligned. If the opposite is true (180° out of alignment) the tendency will be for a momentary boost in rotor torque to aid the primary accelerating torque, and 'hopefully' further accelerate the rotor up to synchronous speed.

    All of this normally happens after the motor has been initially brought up to somewhere around 95% of synchronous speed & DC excitation is then applied - the speed is initially taken to ~95% of SS without excitation, by whatever starting technique is used, such as using amortisseur windings.
    Last edited: Feb 8, 2011
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