Polyphase reaction synchronous motors

THE reaction synchronous motor in its present form (salient-pole rotor without field coils) is one of the oldest types of electric motors, antedating the induction motor by many years. At first it was used only in connection with instruments, such as the oscillograph etc.; later its simplicity and exactness in keeping in step made it the standard driving motor for rectifying devices such as are used for charging low-voltage batteries, supplying high-tension unidirectional current for x-ray and electric precipitation apparatus etc., where the power may amount to several h. p. It is, however, safe to say that the limit of output of the present type is practically reached; its low weight efficiency and poor performance are inadmissible in motors of larger output and seem to justify the general opinion that the reaction motor is inherently inferior to the other types of a-c. motors.