Help me Please..

Discussion in 'General Electronics Chat' started by MrTony, Oct 25, 2014.

  1. MrTony

    Thread Starter New Member

    Oct 24, 2014
    In single phase induction motor why auxiliary winding (start winding) is placed perpendicular to stator winding, that too why capacitor is placed in series with auxiliary winding, What is purpose of capacitor by connecting so, what is capacitor phase split???

    Could anyone please answer me???
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    a single phase cannot create a ROTATING magnetic field.
    This is fixed by the starting winding. Placing it physically offset to put a second set of POLES in the motor and using a capacitor to electrically change the phasing of the current with respect to the main stator poles. With the starting winding now creating new magnetic poles the rotor will experience a rotating magnetic field and startup torque to get it moving.
  3. MaxHeadRoom


    Jul 18, 2013
    The combination of a the cap in series with the start winding inductance will preferably produce a phase shift in current of ~90° in the start winding WRT the run winding in order to get the rotor to revolve, hence Split-Phase.
    With no start winding, the field changes across 180° only, so the rotor field would just oscillate across 180° and produce no motion.
    Last edited: Oct 25, 2014
  4. crutschow


    Mar 14, 2008
    The interesting question (at least to me) is how does a rotating torque continue to be developed when the starting field is shut-off, as in capacitor-start induction-run motors. After all, there's still no rotating field. It comes from considering the single oscillating field as two counter-rotating but opposite fields. At 100% slip (rotor stopped) the net torque from the two fields is zero and the rotor doesn't move (as we know). But, once the rotor rotates, the torque due to the lower-frequency slip frequency in the forward direction is greater than the torque generated by the higher frequency slip in the reverse direction, generating a net forward torque. The higher the speed the lower the torque from the reverse slip and the higher from the forward slip causing an increase in the torque until the motor is slightly below synchronous (at it's normal running speed). For those interested, here's a more complete explanation.