Mercury Arc Power Rectifiers Their Applications and Characteristics

Steel-enclosed mercury arc rectifiers, due to their advantages over rotary converters in efficiency, ease and reliability of operation, and ability to produce high d-c. voltages, are gradually replacing other forms of converters in all fields of application. There are at present 600,000 kw. of rectifier installations, distributed over different parts of the world. Statistical data are given showing the growth of installed rectifier capacity since 1911, the distribution of rectifiers over various fields of application, and their increasing use at higher voltages for railways. The high efficiency and reliability of rectifiers at high voltages will undoubtedly influence the selection of systems and voltages for main-line electrification. Comparative operating figures are given for rectifiers and motor-generator sets at 3000 volts d-c. Several types of Brown Boveri rectifiers and their load curves are shown. Due to the fact that the d-c. voltage of a rectifier consists of portions of sine waves, the voltage wave is some-what undulated. The magnitude of the undulations depends on the number of phases and varies with the load. The effect of the undulations in the voltage wave on the shape of the current wave for various types of loads is discussed, and oscillograms of the voltage and current waves of a rectifier feeding a railway load under various conditions are shown. The effects of the undulations on different kinds of load-batteries, lighting, and power circuits-and on communication circuits paralleling the d-c. feeders are discussed briefly.