This type of motor suffers increased current magnitude and backward time shift as the motor comes up to speed, with torque pulsations at full speed. Permanent-split capacitor induction motor. This is called a permanent-split capacitor motor in Figure below. This requires a motor with two windings spaced apart 90 o electrical, fed with two phases of current displaced 90 o in time. One way to solve the single phase problem is to build a 2-phase motor, deriving 2-phase power from single phase. Single phase induction motors have a copper or aluminum squirrel cage embedded in a cylinder of steel laminations, typical of poly-phase induction motors. If the rotor is started in the reverse direction, it will develop a similar large torque as it nears the speed of the backward rotating phasor. Thus, the single phase coil will develop torque, once the rotor is started.

Little torque (see torque vs slip curve) other than a double freqency ripple is developed from the counter rotating phasor. The rotor will see 200% - 10% slip with respect to the counter rotating magnetic field phasor. Less torque will be developed above or below 10% slip. However, if the rotor is rotated forward at a bit less than the synchronous speed, It will develop maximum torque at 10% slip with respect to the forward rotating phasor. The sum of these two phasors is a phasor stationary in space, but alternating polarity in time. An analogous situation exists in figure d. At 45 o and -45 o (figure c) they are partially additive along the +x axis and cancel along the y axis. When the phasors rotate to 90 o and -90 o they cancel in figure b.

Single phase stator produces a nonrotating, pulsating magnetic field.Īnother view is that the single coil excited by a single phase current produces two counter rotating magnetic field phasors, coinciding twice per revolution at 0 o (Figure above-a) and 180 o (figure e). The single coil of a single phase induction motor does not produce a rotating magnetic field, but a pulsating field reaching maximum intensity at 0 o and 180 o electrical.

Split phase motor pdf