Switched capacitors control feeder regulation with thyristor motor starter

Medium voltage thyristor motor starters have brought new control options for starting large induction and synchronous motors. Starting currents can be precisely controlled and the motor ramped up, to speed slowly. Wear and tear on motors and pumps are reduced by the decrease in over currents and hydrostatic impulses. However, feeder voltage regulation can be a problem, especially in municipal pumping facilities that often are supplied with feeders of relatively low short circuit capacity. Switched capacitors can be used to control feeder regulation during the motor starting sequence. This paper describes the use of this technique in a field installation and illustrates the resulting improvement in stability of feeder voltage during the starting of a large synchronous pump motor.