Why did the circuit breaker fail during the MRT breakdown?

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The circuit breaker failed due to a rusted trip coil, likely caused by inadequate protective covering from a specific manufacturing batch.

The circuit breaker malfunctioned during the October 14 MRT breakdown because a critical component, its trip coil, had rusted. This rust prevented the plunger within the trip coil from moving, which is necessary for the circuit breaker to activate and respond to the short circuit. The investigation indicated that this rust buildup was probably a result of insufficient protective covering associated with a particular manufacturing batch of these components.
Rusted Trip Coil Prevented Activation

The primary reason for the circuit breaker's failure to engage was the corrosion of its trip coil. This component is essential for the circuit breaker's operation. When a short circuit occurred due to a damaged power cable along the Tuas West Extension, the circuit breaker was supposed to activate, but the rusted trip coil prevented this.
Inadequate Protective Covering Identified as Cause

The build-up of rust on the trip coil's plunger was attributed to an inadequate protective covering. This deficiency was linked to a specific manufacturing batch of the trip coils. The current trip coils are constructed from carbon steel with a nickel coating, which evidently proved insufficient in preventing corrosion in this instance.
Replacement with Stainless Steel Planned

To address the recurring issue of rust, all 113 trip coils along the Tuas West Extension are slated for replacement. These components had already been replaced the previous year but will be swapped out again. The new trip coils will be made of stainless steel, a material chosen to prevent future rusting. This replacement is scheduled to be completed by the third quarter of next year.

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Why did the circuit breaker fail during the MRT breakdown?

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