SINGAPORE - Intermittent tripping of the rail power system at multiple locations caused the massive rail service disruption on the North-South and East-West Lines (NSEWL) that occurred on July 7.
The tripping was due to lower electrical resistance pathway at a third rail insulator, said the Land Transport Authority (LTA) and transport operator SMRT in a joint news release on Wednesday.
The weak resistance of an insulator can allow electricity to flow through the insulator to the ground, resulting in a higher than normal voltage difference between the running rail and the ground.
This higher than normal voltage difference, which was exacerbated by the movement of the trains, resulted in the activation of safety mechanisms at multiple locations that tripped the power system.
Water was also found to be dripping onto the third rail cover near an insulator in the stretch of tunnel between Tanjong Pagar and Raffles Places MRT stations.
Mineral deposits with high chloride content were detected from sample residue from the third rail cover and on water collected from the tunnel leak.
The presence of chloride on the insulator, coupled with a wet environment, would have significantly reduced the effectiveness of the insulator, said LTA and SMRT.
SMRT said it has "combed through the NSEWL tunnels to ensure that there are no other leaks with water dripping onto trackside installation".
It also said it has started replacing all third rail insulators, starting with the ones which have shown signs of eletrical resistance weakness. Remaining insulators will be changed by first quarter 2017.
In order to monitor the condition of the insulators, SMRT said it will be installing data loggers at all 47 traction power substations on the NSEWL within the next two months.
The voltage settings for safety mechanisms will also be raised so that the network will be less susceptible to such power trips.
SMRT assured that the the new setting is in line with international standards and commuter safety is not compromised.