Concept Suggestion and Simulation Evaluation of VLD for Reducing Stray Current and Prevent Rail Potential from Exceeding the Standard Voltage

Abstract

In electric railways, rail potential rise because of return current flows in the rail. As the rail potential rises, the return current flows in both rails and the earth. Some railway systems install VLD (Voltage Limiting Devices) to prevent rail potential from exceeding the standard voltage. VLDs are designed to short-circuit between the rail and the earth if the rail potential exceeds a threshold voltage. When the VLD is operated, the rail potential decreases to almost 0V. However, it causes the stray current to increase. The stray current causes an electrical corrosion, which corrodes water pipes, gas pipes, steel bars, and other underground metals. Therefore, it is important to reduce the stray current. We devised a novel VLD concept to reduce the stray current while preventing the rail potential from exceeding the standard voltage. Furthermore, we simulated a suburban line to evaluate the reduction effect of stray current using the novel VLD. It was confirmed that the stray current of the case with the novel VLD was reduced by about 90% compared to the case with the conventional VLDs while preventing the rail potential from exceeding the standard value even momentarily.