Abstract
WHEN an alternating current arc is established in a vacuum tube between a mercury and an iron or graphite electrode, the current only passes during half the time, namely, when the mercury pool is the negative electrode. The alternating current is thus converted into a pulsating direct current, the tube (rectifier) thus acting as a valve allowing the current to flow in one direction and not in the other. In a paper on the steel tank rectifiers operating on the underground railways of the London Passenger Transport Board, read by A. L. Lunn to the Institution of Electrical Engftieers on November 7, a description of the rectifier substations is given and also much useful information of the working of these rectifiers for traction purposes. When the electric railways first started, they were supplied by three phase A.C. from the Lots Road generating station, the current being converted into direct current by means of rotary converters before reaching the trains. These machines were virtually A.c. motors on one side and D.C. dynamos on the other. For running machines, rotary converters are comparatively quiet, and there is little vibration; but in these respects the rectifier is much superior. The substation buildings for operating the traction system of the London Underground are in very densely populated districts, and so the light weight and freedom from vibration of the rectifiers enable appreciable economies to be effected on the building costs. Mr. Lunn looks forward to the time when the continued development of the railway area may lead to the changing-over of a number of existing substations to new supply networks, probably involving a change of frequency. With the present system of rectifiers this would offer no difficulty.
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Rectifiers used on the London Underground Railways. Nature 136, 864–865 (1935). https://doi.org/10.1038/136864c0
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DOI: https://doi.org/10.1038/136864c0