Novel RVSS Motor Control Method to Limit PCC Voltage Sag During Ramp Start

This paper describes a novel reduced voltage soft starter motor control method to limit point of common coupling sag during a ramp start to a certain programmed threshold level. As background information, an across the line full voltage start of an induction motor results in full locked rotor current until the shaft comes up to speed. Whereas a RVSS is employed to electronically limit the current applied to the motor to a fraction of the locked rotor value which has many benefits that will be listed in the presentation. In this paper a real-time hardware in the loop computer simulation, and medium voltage actual laboratory experiments, are used to sweep varying source impedances to compare multiple soft-starter control methods to the novel sag controlled sag method. The soft starter sag control method may be appreciated in weak source implementations such as rural installations and additionally in process control where motor starting sequences and loading at the time of ramp start can be dynamic.