Self‐excited synchronous induction motor

A synchronous-induction motor, with the features of both a synchronous motor and a wound-rotor induction motor, far excels other synchronous motors in starting characteristics. However, a major drawback of the synchronous-induction motor is the need for an excitation power supply with low-voltage, large-current power rating. For this reason, its driving equipment becomes large, and increases overall cost. This paper proposes a new synchronous-induction motor, absent the problems involved in making the motor a self-excited type. It employs the second-space harmonic component of armature reaction field to obtain the self-excitation of the field system, and installs a harmonic winding, which is used for extraction of an excitation power, in the rotor. This new self-excited motor has the following advantages: (1) the driving equipment is small, since no excitation power supply is involved; and (2) due to the effect of the series characteristic by which the field current varies in proportion to the load current automatically, the motor can be operated with a good power factor. In the present paper the structure and operating principle of the new motor are explained and the basic characteristics are also investigated by means of a simple analysis and experimental results with a 1.5-kV trial machine.