Train failure was probably due to third rail insulation
The insulation of the MRT system's third rail, which supplies power to trains, is the likely cause of the massive breakdown on July 7, SMRT said yesterday.
The breakdown disrupted service on the North-South, East-West Line (NSEWL) for more than two hours during the evening rush hour.
SMRT's investigations have narrowed down the likely cause to this insulation, which is part of the trackside infrastructure that protects the power cables supplying the third rail.
SMRT said that "intensive, round-the-clock investigations" and re-enactments of the incident "point to the likelihood that the insulation of the third rail could have affected the supply of traction power".
This, in turn, led to the tripping of the Touch Voltage Protection Relay along multiple stretches of the lines.
The relays are a safety measure, meant to protect commuters from unsafe "touch voltage".
SMRT's investigations covered 200km of train tracks, all 67 power substations supporting the NSEWL, all 115 trains used on July 7 and another 26 trains at depots.
Re-enactments last weekend have ruled out two earlier suspected causes: two track voltage balancing cables, and a relay in a power substation.
As part of SMRT's pledge for an independent consultation of the incident, the operator has approached international rail operators such as London Underground for their views on SMRT's preliminary assessment.