Abstract :
D-c. substations designed to meet the demands of heavy railway terminal service are described in this paper. This d-c energy is furnished at 1500 volts from seven substations located in the Chicago district and owned and operated by the power companies. In addition to 1500-volt supply for traction purposes, 4000/2300-volts alternating current is provided for the railway company´s light, power, and signal system. Approximately 80 per cent of conversion capacity is in synchronous converters and the remainder in mercury rectifiers. Reasons for selecting the latter units are given as well as some of the characteristic features of them. To meet the rigorous requirements as to voltage and current demands under the agreement with the railway company, the conversion units have a rating of 300 per cent load for one minute. The synchronous converters are of the field-control type, and in order to hold the d-c. voltage to definite values for any load within the rating of the units, and to maintain the reactive current of the unit within the safe limits, there is provided, common to all the converters in a substation, a counter e. m. f. regulating set, a four-circuit heostat, and a voltage regulator. High-speed air breakers are used on the d-c. side of the units and all 1500-volt feeders. Another feature of interest is the use of truck-mounted enclosed switch units on both the high- and low-tension sides of the substation, This type was selected in order to eliminate certain operating hazards which exist with fixed type switching arrangements, and to provide the customary factors of accessibility and maintenance. In operating experience, the substation equipment has met all expectations, the performance of the synchronous converters and high-speed breakers being exceptional, while confidence in the mercury rectifier not lessened.
