Response analysis of saturable reactors and tap changer in an aluminium smelting plant

Aluminium smelters are one of the peculiar loads, which typically represent a series of electrolytic cells supplied by a multi-pulse rectifier system. In order to address the complexity involved in the modelling of a smelting plant, the impact of multipulse configurations and its connection to HV networks and control aspects of load current should be considered. This paper addresses the issues related to the control of DC current using saturable reactors for different alumina feeding mechanisms in a typical smelter. The saturable reactors are modelled as variable inductors of which the magnitude is controlled using a proportional-integral control scheme. A smelting plant with a twelve pulse rectifier system and variable DC load has been modelled in PSCAD®/EMTDC©. The plant is connected to the AC network through 220 kV/110 kV transformer with tap changing facilities to control the secondary voltage and associated load current of the smelter. The simulation results are reported for the control of DC current under varying load conditions.