Abstract
Stray earth current associated with DC powered transit systems can create problems for industries that rely on buried metallic facilities. In 1981 the Toronto Transit Commission, with the co-operation of local utilities, embarked on a program to reduce the magnitude of stray earth current associated with the traction power system. While both surface and subway DC powered systems are in operation in the Metropolitan Toronto area, the work effort to date has concentrated on the subway system due to the higher power requirements of the vehicles. The objective of this work has been to increase the effective DC negative system-to-earth resistance levels by reinsulation of select areas along the subway system and by the elimination of electrical grounds to the DC negative return system. The goal of the project is to have a once intentionally electrically grounded DC return system restructured to a totally isolated negative return system.
This paper presents a brief overview of the DC powered transit systems presently in operation in the Metropolitan Toronto area and discussion of future projects. The paper will concentrate on recently developed mitigation techniques and practices employed by the Toronto Transit Commission to electrically isolate the DC negative return circuits of the subway traction power system from earth. The electrical isolation program reduces the level of stray earth currents and provides for a safe electrical environment for passengers and Commission personnel. In addition, the impact the electrical isolation program has had on local utilities will be discussed.
