Configuring the Parameters of a RVSS to Start a High Torque Induction Motor Load with a Soft Pull-In

This paper describes the approach to configuring the parameters and overall philosophy of controlling a reduced-voltage soft-starter (RVSS) for a high-torque induction motor load. As long as the induction motor's blocked rotor, breakaway, and pull-up torque are adequate for the torque-speed curve, an RVSS can be controlled and programmed to adjust its thyristor firing patterns to bring the motor up-to-speed and transition it to a bypass running state. The other necessary concern would be whether utility Sag at the PCC would be acceptable when the programmed current limit of the RVSS is at its threshold. Otherwise, an adjustable frequency drive (AFD) may be of interest in replace of the full-voltage across-the-line start or RVSS start to better the torque-per-amp ratio and sag at the point of common coupling (PCC).