Unlike the earlier case without the running capacitor in the auxiliary winding, since the running capacitor is able to make the impedance of the auxiliary winding capacitive and as a result, the main winding current and the auxiliary winding current have a phase displacement of around 90 degrees, and the main winding voltage V main and the auxiliary winding voltage V aux can be kept in phase. The main winding voltage and the auxiliary winding voltage can be presented in Eqs. Similar as the earlier case, the main winding of the SPIM is connected between the three-phase inverter connection points a and b, while the auxiliary winding is connected to the connection points c and b. The scheme of three-phase voltage source inverter and the SPIM is using a running capacitor in the auxiliary winding. If a single capacitor is used for both starting and running, the starting torque is 0.5–1 times full-load value and the power factor in running is near unity.įig. Ideally, however, the value of capacitance for running should be about one-third of that for the best starting. If the capacitor is left in circuit continuously ( capacitor-run) the power factor is improved and the motor runs with less noise. For economic reasons the capacitor is as small as is consistent with producing adequate starting torque, and some manufacturers quote alternative sizes for various levels of starting torque. The capacitor size is from 20–30 μF for a 100 W motor to 60–100 μF for a 750 W motor. Maximum torque occurs for a capacitance such that the auxiliary current leads the main current by (½π = α)/2.
#Induction motor winding series#
MG Say PhD, MSc, CEng, FRSE, FIERE, AGCI, DIC, JF Eastham, in Electrical Engineer's Reference Book (Sixteenth Edition), 2003 Capacitor split-phase motorĪ greater phase difference (ϕ m − ϕ s ) can be obtained if a series capacitor is substituted for the series resistor of the auxiliary winding. The direction of motion in motors of types 1, 2, and 3 can be changed by reversing the connections of either the main or the auxiliary windings.
The auxiliary winding is a so-called shading coil consisting of an uninsulated short-circuited copper strip embedded into one of the main poles and spanning about one-third of its pitch. Shaded-pole motors, such as used in fans. The auxiliary winding is connected only during starting. The auxiliary winding is wound with fewer turns and much smaller size of wire than that of the main winding, so that it has a considerably greater resistance-to-reactance ratio. The auxiliary winding is connected through a capacitor only during starting. 2.Ĭapacitor-start motors, such as used in refrigerators. The auxiliary winding is connected permanently to the supply through a capacitor.
In order of decreasing magnitude of developed torque and cost, one may list the following: 1.Ĭapacitor-run motors, such as used to drive the compressors in air-conditioning units. The required phase difference in the currents flowing in the two windings when they are fed from the same voltage is obtained by the different nature of the circuit impedance. In all cases the auxiliary winding is displaced in space from the main winding.