Increasing copper production in electrochemical plants using new small transformer - Rectifiers in parallel with existing power rectifiers

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The production of copper in electrochemical plants requires a large amount of dc current to obtain the desired copper product output. The dc current is supplied by high-current thyristor-based controlled rectifiers. Many copper plants use rectifier systems designed with two or more similar transformer–rectifiers connected in parallel to obtain the desired dc current output. Parallel rectifier systems may use 12 or 24 pulses depending on rated values of dc current. To maximize copper production when higher quality mineral is being processed, the dc current needs to be increased to values that exceed the designed rated output value of the transformer–rectifier. To solve this problem, a smaller supplementary low-current rectifier can be connected in parallel with the existing rectifiers to achieve the desired dc current output. This solution proves to be economical compared with other alternatives such as increasing the number of cells in the process or replacing the existing transformer–rectifiers with larger ones. This solution has been implemented in several copper plants with satisfactory results. As an example, a 2 $\times$ 25 kA 12-pulse rectifier installation was modified to a 60-kA 18-pulse rectifier installation by adding a 10-kA auxiliary transformer–rectifier in parallel with the existing rectifiers. This modified design has continuously and successfully operated for the past five years. This paper will describe the requirements for determining if an auxiliary transformer–rectifier is the best solution for increasing the total dc current capacity.