The economics of direct current railway distribution: With particular reference to the automatic substation

Abstract

The comparatively recent development of the full automatic substation and also the automatic substation combined with remote control, has served to re-open the entire subject of the economics of distribution. But quite aside from the questions that the automatic substation has presented, the great fluctuations in the prices of materials and of labor have made necessary renewed study of this subject. In other words, the proper design of a distribution system should represent a balance between all of the different items of cost that go to make up the total cost of power. Any change in the relative cost of materials as against labor or of a certain class of materials as against another class of materials tends to upset such a balance. Now that we begin to emerge from the unsettled conditions of the past few years during which the old relationships have been substantially changed, it is necessary to ask the question whether or not the rules by which distribution systems have been planned in the past still apply. More specifically, it is the purpose of this paper to determine, first, the relations that govern the size of feeders and the correct feeder layouts for any given arrangement of substations, and second, the principles underlying the correct location, size, and type of substations, assuming the fullest development of automatic and semi-automatic control. There is involved also the important question of stray currents. Regardless of the merits of the electrolysis controversy, the minimizing of stray currents is certainly to be desired by the electric railways. The most effective method of accomplishing this is increasing the number of distributing points. If a large number of distributing points be justified from an economic standpoint, and if furthermore this be found practicable from an operating standpoint, then the problem of electrolysis may perhaps cease to exist. Thus the inquiry is doubly pertinent. The cost of distribution in large cities of the size of Cleveland, Detroit, or St. Louis, comprising the carrying charges on the feeder, the heating losses in the feeders and the carrying charges on the equipment necessary to supply these losses, is considerably in excess of $200,000 per year. It is apparent that a careful study of this item of cost will more than likely be justified by the savings that will result. There are not at the present time sufficient accurate data on cost and performance of automatic substations to make possible a precise analysis of specific cases. In lieu of this it is the authors' purpose to show limiting conditions and by example to illustrate the relation of the various determining factors to the final cost.