Discussion on “track-circuit signaling on electrified roads”, at Niagara Falls, N. Y., June 28, 1907

This paper is quite special in its scope and is valuable for the information it gives, but is not apt to be fruitful of general discussion. I have been interested to note during the reading of the paper, and also in my observation during the last few years of this signal development, of the general course of that development and the effect of the electrification of railways on signal work. At first on the ordinary steam road, the only electricity used in connection with the track system was the small amount employed in connection with the signals. The use of the track, however, for carrying direct current for railway motors has caused some voltages to be introduced which begin to affect the signal circuit and they have to be taken care of in ways which when they are worked out and explained seem simple and adequate, but did not seem so simple when the difficulties first arose. The introduction of single-phase alternating current and the use of the rails for conducting this current again introduces a new kind of disturbance in the signal system. It is interesting to note how the signal work has followed these various intrusions of greater currents. One rail was set aside for signal work, and later on the signal system adapted itself to the condition existing when both rails were used for propulsion current. The signal engineer follows the example of the railway engineer and gets into alternating current; if the alternating current in the railway is bad for his work he cures the evil by adopting alternating current himself. He solves the frequency question by going to a high frequency instead of a low one. This also illustrates the amount of electrical engineering which can be applied to what most of us who have not come in contact with this work at all have probably considered a very simple sort of thing, but the grade of engineering work and the knowledge and ingenuity required in devising these systems, with the remarkable reliability and excellent way in which they perform their work, is something to elicit our admiration. There is still another source from which other currents may come and affect the signals, which I understand has been characteristic of one installation, and that is when the tracks were bonded together for the operation of the railway these track connections formed an inviting path for currents from adjacent railways which were strolling through the earth, hunting convenient paths by which to get home, and these currents got into the tracks, and the signal apparatus producing some unexpected combinations of signals. This illustrates again the interference between different kinds of currents and the need of the signal engineer to be alert for their avoidance.