ABSTRACT
The running rails of most DC powered railway transit system are used as the negative return conductor for traction current. This arrangement has considerable economic benefits. Depending on the earthing strategy adopted for the running rails, the running rails negative return arrangement can result in considerable rail to earth voltage rise and stray current activities during train operations. A floating running rails negative return has been adopted in the North East Line (NEL) Mass Rapid Transit (MRT) System and this arrangement is similar with other existing MRT lines in Singapore. NEL commenced revenue service on 20 June 2003. In 2006 and 2008 there were a number of traction power outages during revenue service due to excessive rail to earth voltage rise causing protection relays to operate. In 2006 the outages were caused by the interruption of negative return to the traction current of a locomotive during operation. And separately in 2008 inappropriate earthing arrangement was the cause of the excessive voltage rise. This paper discusses the two different case scenarios, investigations and tests that were carried out to identify the root cause of the excessive rail to earth voltage rise and the countermeasures implemented. The countermeasures have been effective as there has been no occurrence of similar incident since.
Keywords: DC transit system, Running rails, Rail-earth voltage rise, Stray current, 64P protection, Traction.
