Polyphase supply circuit for variable speed motor - has separately controlled frequency and volts without mechanical intervention

摘要

The polyphase supply circuit, for a variable speed motor, has frequency and voltage controlled and adjusted separately without mechanical intervention. The selection circuit for the frequency of the alternating current is provided for a star configuration. The control circuits have reference voltages derived from the difference between the phase voltages and the neutral voltage. An isolating transformer is connected between the mains supply and the control circuits. A first protection switch is connected between the transformer and each control circuit. A second switch is provided to protect one phase against overload.