Operational and safety considerations in designing a light rail DC traction electrification system

This paper gives an overview of an integrated approach to operational and safety issues when designing a DC traction electrification system (TES) for modern light rail and streetcar systems. We first develop the human body electrical circuit model and define tolerable step and touch potentials derived from IEEE Standard 80. We then identify and analyze touch voltages that are commonly present around the rails, at station platforms, at traction power substations. Operational and safety topics discussed in this paper include: applicable codes and standards for electrical safety; traction power substation (TPS) grounding; detection of ground faults; DC protective relaying schemes including rail-to-earth voltage sensing and nuisance tripping, and transfer tripping of adjacent substations; TES system surge protection; OCS sectioning including feeder disconnect and bypass switches; electromagnetic and induced voltage problems that could cause disturbances in the signaling system; DC stray currents that can cause corrosion and damage to the negative return system, underground utilities, telecommunication cables, and other metallic structures; and emergency shutdown trip stations (ETS). To ensure safety of the project personnel and the public, extensive testing and proper and safe equipment operation, are required. The testing includes factory testing of the DC protection system, first article inspection of critical TES components, inspection and field testing during commissioning. In addition, safety certification must be accomplished before the TES system is energized and put into operation.