Measures instituted to prevent similar incidents
The Land Transport Authority (LTA) and SBS Transit (SBST) have completed investigations into the causes of the rail service disruptions on the North East Line (NEL) that occurred on 13 and 26 October 2015.
Component malfunction in electrical switchgear
2. On 13 October, train services were disrupted between Farrer Park and Hougang stations due to a power fault triggered by a malfunction of a component in the electrical switchgear at a substation that supplied electricity to power the trains running between these stations. This caused the main circuit breaker to trip.
3. As a result of the trip, power was diverted to a backup breaker which also tripped.
4. LTA and SBST have since determined that the original manufacturer protection setting of the backup breaker was overly conservative, and, as an interim measure, have increased its protection setting to cater for the projected maximum load of the network, which the electrical network is able to support safely.
5. For the longer term, LTA and SBST are working together to enhance the power system to minimise the likelihood of a recurrence.
Damage caused by arcing
6. In the morning of 26 October, a new train undergoing testing damaged the overhead catenary system (OCS), which supplies power to the trains, when it was returning to the depot via one of the reception tracks. Power to the mainline tracks between Hougang to Buangkok (both bounds) was switched off to facilitate urgent repair works. This affected the launching of trains to the mainline, and hence the disruption to NEL services. Power to the rest of the mainline and depot was not affected.
7. Investigations revealed that the train was being manually driven from the mainline back to the depot when the driver saw sparks from above the train and stopped the train immediately. The train stopped at a stretch where the mainline and depot OCS wires overlap, resulting in arcing between the mainline and the depot OCS wires. The sustained arcing caused the OCS wires to melt, which eventually snapped. (Arcing occurs at this overlap point because of the voltage difference between the mainline and depot OCS. This is not a problem during normal operations as the NEL trains are driverless and will not stop at this overlap point to cause sustained arcing.)
8. As an interim precautionary measure, SBST has marked all overlap zones on the reception tracks to indicate these as non-stopping zones.
9. LTA and SBST are working together to enhance the design of the OCS to minimise the likelihood of a recurrence, including reducing the electrical voltage difference between the two different sections of OCS wires at the mainline and depot interface, in case trains still stop at this stretch.
10. The LTA-SBST Joint Team will closely monitor the implementation of these measures.