Control system for AC induction motor

A control system for coupling the primary windings of an AC induction motor to a source of three-phase electric power, comprising;

• a wye-delta starter for coupling the primary windings to the power source in order to apply power to the induction motor and which, in response to starting, connects the primary windings into a wye-connection to limit the inrush current normally occurring at start-up;
• power sensing means for generating a control signal which is directly proportional to the power applied to the induction motor;
• and differential comparator means responsive to said control signal and to an adjustable reference signal, representing a preselected power input level, for generating an actuating signal for switching the wye-delta starter between a first condition, wherein the primary windings are connected in a wye-connection, and a second condition wherein the primary windings are connected in a delta-connection,
• the first condition being established, to effect energy savings, during light loads when the power applied to the induction motor is below the preselected power input level, whereas the second condition is established during heavier loads when the power applied to the motor is above the preselected power input level.