We have to choose capacitance values that either optimally balance the magnetic fields at a given speed (e.g. But, the capacitance required to creates the ideal current phase shift will be different at every slip value. Ideally, we want the current in an "auxiliary winding" to lead the main winding current, and we can use a capacitor to acheive this. This adds additional complexity if two balanced winding currents are to be obtained from a single phase supply - the power factor of the winding changes with slip. Using knowledge of three-phase induction machines, we know that the impedance of a winding is a function of slip. This can be seen in the animation in Fig. If the supplies are unbalanced, or the phase angle is not exactly 90°, there will be a combination of a pulsating and rotating effect. If the phase supplies are balanced (the same per-unit mmf), with a 90° electrical phase angle between the currents and a 90° electrical space angle between the coils, then the result is a purely rotational field with no pulsations. 4, there are two phases supplying the motor. The majority of single phase indcution machines work by applying two phase currents to the motor (two windings connected to the same supply voltage, with different impedences to create different phase angles for the currents). There are a number of different types of single phase induction machine, which have slightly different approaches to creatingĪ rotating field at starting. However, single phase motors can be made, so there seems to be a contradiction in what Pulsating fields, not rotating fields and pulsating fields do not produce torque. Indicates a problem, single phase supplies produce the cross product of flux densities will be zero, the motor produces no torque. In the diagram above, both the stator and rotor flux densities will act in the y-direction.
The voltage induced in the rotor circuits willĬause a current to flow, producing a flux density to oppose change in the stator flux linking theĬircuit.
If an ac supply is connected to the stator winding, a pulsating flux density willīe produced, which will link the rotor circuits. The significant difference is, of-course, that there is only aĬonsider the motor schematic shown in Fig. Of a three phase motor: an ac windings is placed on the stator, short-circuited conductors are Single phase induction motors generally have a construction similar to that