Improvements in mercury arc rectifiers

THE PRINCIPLE of building the larger capacity rectifiers in sectional form was discussed in a paper presented before the Institute at the 1932 winter convention. Obviously, the successful achievement of a sectional rectifier, without its becoming prohibitively large, involved the development of a rectifier section much reduced in size from the familiar conventional rectifier of 500 kw to 1,000 kw capacity. Due to the characteristics of the device, this reduction in size of section inevitably resulted in a corresponding reduction in arc drop with a further enhancing of the advantage of the sectional arrangement. The design was based on a 1,250-amp section, which is approximately the rating above which difficulties due to size begin. The 1932 paper briefly described the first design of sectional rectifier. Since that time, considerable improvement has been made both as to performance and convenience of operation. The present paper describes the 2,000-kw 625-volt unit being installated on the Fulton Street line of the independent subway system of the city of New York for the New York board of transportation. This unit is typical for any capacity above 750 kw at 600 volts. The paper also briefly describes smaller rectifiers for capacities below 750 kw.