Reverse Generator Voltage with Unidirectional Trinistor Control Rectifier

Most metal mill drives use separate d-c generators for accurate speed control. Generator voltage and motor speed is controlled by an unidirectional trinistor control rectifier which supplies excitation to the generator main field. To reverse the drive, generator voltage must be reversed either by using a bias field or by connecting the trinistor in buck-boost across the single-machine field. In either case, the a-c nature of trinistor voltage tends to wipe out reverse ampereturns and prevent drive motor reversal. An external reactor in series with one machine field absorbs the a-c voltage and allows reversal of the drive motor. The size and inductance of the external reactor is to be determined from expressions and methods developed in this paper.