Effects of Layout on Current Distribution in Paralleled Thyristors of High Current Rectifiers

In electrochemical process of copper or aluminum it is necessary to have very high DC controlled currents, which are provided by thyristor rectifier-transformer units. Due to the large DC load current, several thyristors must be connected in parallel in each secondary phase. It is very important to operate with a symmetrical distribution of current in paralleled thyristors. The distribution of current between paralleled thyristors also depends on rectifier layout. Even more, current distribution can change in some way over time. The current in each thyristor is not given by total secondary phase current divided by the number of thyristors in parallel, as in ideal cases. In this paper several real cases of current distribution are analyzed with respect to the rectifier layout and also how this distribution changes over time. This paper intends to be helpful for field engineers who work on high current rectifier maintenance.