Southbound train service on a portion of the North-South Line was delayed by about 20 minutes on Thursday after SMRT engineers detected and repaired a sagging third rail.

SMRT spokesman Alina Boey said the defective third rail between Ang Mo Kio and Bishan MRT stations was detected Thursday morning by a Linear Variable Differential Transformer (LVDT) placed on a train. The LVDT is a surveillance instrument that monitors track conditions and any anomalies on the third rail, which supplies power to the trains.

Ms Boey said power was shut down at Ang Mo Kio station between 12.05pm and 12.25pm for engineers to go on the track and carry out repair works. Normal service resumed at 12.25pm.

Service announcements were made in trains and within the stations to inform commuters to expect an additional five minutes of travel time between the two stations, she said. She thanked commuters for their cooperation.