Discussion on “motor-generator sets vs. synchronous converters in mine substations” (Hoen), and “mine substations; their construction and operation” (Booker), Pittsburgh, Pa., April 10, 1914. (see proceedings for April, 1914)

W. A. Thomas: Unquestionably from the standpoint of economy the synchronous converter is superior to the motor-generator set, but in a careful analysis of the mining conditions, and the ultimate results to be accomplished, the question of the kilowatt-hours per ton in transformed energy constitutes a relatively small proportion of the total cost. The method of distribution of the direct current which has been converted has a great bearing on this question. As pointed out in Mr. Hoen's paper, the energy in the small mine is carried through one opening which is the main entry, and when the bituminous mine, particularly, as distinguished from the anthracite mine, comes to the commercial condition requiring electric haulage, the power is mainly consumed some distance from the entry. The distance of the point of consumption from the mine entry in the average bituminous field is probably upwards of a mile.