Energy economiser for polyphase induction motors - has two triacs conducting differently at very light loads for smooth operation and max. energy saving

摘要

A standard three-phase induction motor starts with all three of its input connections connected to the three-phase power line. Two of these connections are through triacs which remain continuously conducting below the motor's particular most energy-efficient speed, which is above about 95% of synchronous speed. This assures full starting torque and undiminished overload handling capability. The triacs, in response to a control signal, may open the circuits over a sufficiently wide portion of the sine wave input voltage to maintain the particular efficient speed under all rated load conditions. The DC control voltage which determines the operation of the triacs is generated by a frequency discriminator circuit which receives its information from a load detecting device that is frequency modulated by load/speed related properties inherent in induction motors.