The great 7/7 mystery solved

Three weeks ago (7 Jul), trains across North-South and East-West lines (NSEWL) were disrupted, with 250,000 commuters affected by the worst MRT breakdown in history.

That night, Singapore’s train network looked like this:


What really happened?

SMRT has since solved the great mystery of the massive rail disruption, attributing it to a third rail insulator due to “weak electrical resistance”. This caused electricity to flow through the insulator and led to a higher-than-normal voltage difference between the ground and the running rail, thus causing a power trip.

Electrical power to trains are supplied by this third rail.

Other factors also came into play.

Let there be salt water

A tunnel leak between Tanjong Pagar and Raffles Place resulted in water dripping onto the third rail cover. Tests revealed that there was mineral deposits with high chloride content. Copious chloride led to insulator surface contamination, which reduced its effectiveness.

The situation was aggravated by the trains’ movement, which brought about the activation of a safety feature called the 64P, also known as the Touch Voltage Protection Relay, at numerous locations in the transport network and tripped the power system.


Leak was spotted before the incident

We know what you’re thinking: how come no one took action?


Well, according to SMRT’s managing director of trains, Lee Ling Wee, the leak was spotted by a patrol officer the Saturday before, who classified it as “non-urgent”. Unfortunately, a downpour took place the night before the breakdown.

So what now?

SMRT is in the midst of replacing all third rail insulators, and should be completed by early 2017. Insulators with signs of electrical resistance weakness will be replaced first – such as the stretch near Commonwealth.

In addition, all 47 NSEWL traction power substations will be fixed with data loggers within the next two months to keep an eye on the insulators’ condition.

They will also be de-sensitising the 64P from 136V to 200V so it is less vulnerable to power trips.

Hopefully, this means we’ll be experiencing fewer train breakdowns.


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Featured image via Ali Muhd
With reference to The Straits Times, Channel NewsAsia