초록 ▼

The specification discloses a system for preventing current overload in a three phase dual speed A. C. motor in both high and low speed modes. The system includes current transformers for sensing the current level in each of the three phases applied to the motor. Circuitry is provided to detect the

The specification discloses a system for preventing current overload in a three phase dual speed A. C. motor in both high and low speed modes. The system includes current transformers for sensing the current level in each of the three phases applied to the motor. Circuitry is provided to detect the occurrence of a current level above each of a plurality of levels depending upon the speed of the motor. Circuitry is responsive to the detection of an overload current level in order to operate a switching transistor to terminate conduction of a triac in order to terminate the current flow through the phases. A light emitting device is connected to the switching transistor to emit light upon the occurrence of the overload condition. A light sensor senses operation of the light emitting device and initiates a timing cycle by a timing circuit during which the triac may not be rendered conductive.

대표청구항 ▼

A system for preventing current overload in a multiphase multi-speed alternating current motor in low and high speeds comprising: current transformers for sensing the current level in each of said phases of said motor, a resistor divider network connected to each of said sensing means and including

A system for preventing current overload in a multiphase multi-speed alternating current motor in low and high speeds comprising: current transformers for sensing the current level in each of said phases of said motor, a resistor divider network connected to each of said sensing means and including a low speed configuration and a high speed configuration, means responsive to low speed operation of said motor for connecting the outputs of each of said low speed configurations to a summing location and further responsive to high speed operation of said motor for connecting the outputs of each of said high speed configurations to the summing location, a differential amplifier responsive to the voltage at the summing location for generating an overload signal upon the occurrence of an overload current in any of said phases, a triac connected to control current flow through said phases, a switching transistor operable in response to said overload signal for switching said triac to terminate current flow through said phases, a light emitting device connected to said switching transistor for emitting light upon the occurrence of said overload signal, a timing circuit including a field effect transistor connected to control said switching transistor and a timing capacitor for controlling the state of the field effect transistor, and light sensor means for sensing said light and for initiating a timing cycle by said timing circuit during which said triac may not be switched to allow current flow through said phases.