Two new methods of accelerating electric motors automatically

The first of the two methods discussed in this paper is particularly applicable to a-c slip-ring motors. Series-resonance circuits responsive to the variation in rotor frequency with motor speed provide a means of accelerating the motor automatically, while a series-parallel resonance circuit similarly connected to the rotor can be used to protect the motor when “plugged” or suddenly reversed. The sensitive response of the latter circuit within a narrow frequency range makes possible its use as a “zero-speed” switch.