EXCITER FOR SYNCHRONOUS MOTOR

PURPOSE:To omit an exciting thyristor by forming a rectifying bridge of a mixing bridge rectifier, and providing switch function in the thyristor arm in the rectifier. CONSTITUTION:When a motor is started as an induction motor, the overvoltage of the slip frequency induced at the field coil 3F is absorbed by a discharge circuit 51 and the motor is accelerated. A closure instructing circuit 7 detects the slip frequency voltage signal from the voltage dividing tap A of a discharging resistor 52, selects the optimum phase state to the synchronizing acquisition of the slip frequency voltage and outputs an excitation signal (1). In this manner, an oscillator 8 and a gate circuit 9 switches ON the thyristor 202 of the rectifying bridge 201, and applies the DC output voltage of the AC exciter 1 to the field coil 3F.