Thyristor rectifiers are common in industry in the United States and the world and have been for many years. Functions have included electrolysis, large drives (such as rolling mills and hoists), and heating. These units range from 100KW to over 10MW and have been emplyed for the past 25 years in large DC applications which required voltage control. There are dozens of manufacturers with extensive experience in manufacturing controllable rectifiers, and the technology is thoroughly established. Hundreds of technical papers have been written based on operation of these rectifiers including their characteristics and their effect on plant and utility systems. Suddenly, the American transit industry discovered "Thyristor Rectifiers" (typically known as controlled rectifiers or SCR rectifiers in the United States) and, at least in the press, traction power engineering changed completely. Claims of lower energy costs, lower capital costs increased spacing, lower maintenance costs, and even elimination of the need for DC circuit breakers usher in this "discovery". The facts are the cost is higher, the maintenance is higher, the spacing is primarily driven by other factors, there are many reasons that DC breakers are necessary, and controllable rectifiers introduce a host of problems which have had to be addressed (usually successfully) in industry for over twenty years. This is not to suggest that controllable rectifiers do not provide advantages, it is just that they are not magic bullets.
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