Abstract:
The application of thyristor to induction motor speed control has resulted in a number of unconventional supply systems. One such technique, which has been successfully employed in a number of applications, variable voltage control by means of symmetrically triggered thyristor in the stator phases.
The present work deals with fabrication of a three phase a.c. regulator with antiparallel SCRs in each phase triggered by appropriate analog control circuit in open loop mode. Experimental investigation of regulator performance has been carried out. The waveforms of voltage and current at regulator output are recorded with resistive and induction motor load under (a) Delta connection (b) Star connection with isolated neutral and (c) Star connection with neutral connected to supply neutral. The nautre of these waveforms are explained through qualitative graphical analysis. Load tests on the induction motor under stator voltage control have been carried out with a d.c. generator type of load. Performance of the motor under thyristor control is evaluated and compared with that under variac control.
