Excitation rectifier schemes for large generators

Electric-power generators require field systems supplied by a direct current, and the use of d.c. exciters has, in general, been an obvious choice for units with a rating of up to 200 MW. As the ratings of generators increased, so did the excitation-power requirements, and it became clear that, if exciters were to be directly driven from the main generator shaft, the d.c. exciter was no longer the best machine to meet the new demands. The a.c./d.c. excitation scheme was therefore developed, and the semiconductor rectifier became an indispensible part. The paper reviews the development construction, testing and operation of excitation-rectifier schemes associated with large generators of the Central Electricity Generating Board.