Design Of Single Phase Capacitor Start Induction Motor
von extic · 27.06.2017
This work attempts to present a unified approach to the analytical prediction of the electromagnetic torque of these machines. Classical d-q axes formulation requires that the reference frame should be fixed on the frame where the asymmetries arise, i. The asynchronous torques that characterize the induction motors are modelled in a stationary reference frame, where the d-q axes coincide with the physical magnetic axes of the stator windings. For the permanent magnet motors, that may exhibit asymmetries on both stator and rotor, the proposed solution includes: As in single-phase and two-phase systems the homopolar component is zero; each symmetrical component — negative and positive — is further analysed using d-q axes theory.
The superposition principle is employed to consider the magnets and rotor cage effects. The developed models account for the most important asymmetries of the motor configuration. These are, from the stator point of view, different distribution, conductors' dimensions and number of effective turns, non-orthogonal magnetic axes windings and from the rotor point of view, asymmetrical rotor cage, variable reluctance, and permanent magnets effect.
The time and space harmonics effect is ignored. Test data are compared with the computed data in order to observe how the simplifying assumptions affect the level of accuracy. The analytical prediction methods make possible torque computation according to the nature of the torque being computed, namely, induction, reluctance and excitation permanent magnet.
One often-used method is the Split Phase motors. Another method is the Capacitor Start Induction Run Motors. When a capacitor is so introduced, the voltage lags the current by some phase angle. In these motors, the necessary phase difference between the Is and Im is obtained by introducing a capacitor in series with the starter winding. The capacitor used in these motors are of electrolytic type and usually visible as it is mounted outside the motor as a separate unit.
During starting, as the capacitor is connected in series with the starter winding, the current through the starter winding Is leads the voltage V, which is applied across the circuit. But the current through the main winding Im, still lags the applied voltage V across the circuit. Thus more the difference between the Is and Im, better the resulting rotating magnetic field. It is important to point out from the phasor diagram that the phase difference between Im and Is is almost 80 degrees as against 30 degrees in a split-phase induction motor.
Thus a capacitor-start induction-run motor produces a better rotating magnetic field than the split-phase motors.