36 EngineeringContact Lines 118 (2020) Heft 1 Abnormal wear of third rail ramps in a DC 750V metro line Etienne Cazaudebat, Paris (FR) Abnormal wear is observed on the third rail of a Middle East metro, more specifically in the so-called high-speed acceleration ramps. After having found the main root cause, which is electrical arcing, trials on site and a benchmark from other metro systems have been performed to get an acceptable solution for high-speed sections thanks to multi-criteria analysis. Anormaler Verschleiß bei Aufläufen der Seitenstromschiene bei einer U-Bahn-Linie DC 750V An der dritten Schiene einer Nahost-U-Bahn wird ein anormaler Verschleiß beobachtet, insbesondere an den so genannten Hochgeschwindigkeits-Beschleunigungsrampen. Nachdem die Hauptursache, nämlich elektrische Lichtbögen, gefunden war, wurden Vor-Ort-Tests und ein Benchmark mit anderen U-Bahnen durchgeführt, um mittels einer Mehrkriterien-Analyse eine akzeptable Lösung für diese Rampen zu erhalten. Usure anormale des rampes de troisième rail d’une ligne de métro 750V CC Une usure anormale est observée sur le troisième rail d’un métro du Moyen-Orient, en particulier sur les rampes d’accélération dites grande vitesse. Après avoir trouvé la cause principale, nommément les arcs électriques, des essais sur sites ainsi qu’un benchmark d’autres métros ont été réalisés afin d’obtenir une solution acceptable pour les rampes grande vitesse, grâce à une analyse multicritère. 1 Introduction Few years after the opening of a Middle East metro network, excessive wear of the third rail was discovered. To gain an outside view, SYSTRA was commissioned to investigate the causes and to develop suggestions and recommendations. This paper explains the technical approach, beginning with the context, followed by a detailed description of the issue and the root cause, and finally by presenting the solutions found through on-site trials and benchmarking with other metro systems 2 Context This 75 km-long metro network is fully automated and driverless, allowing 200 million passengers per year on the two lines. The 750V DC power supply is provided by a bottom contact composite conductor rail with a stainless steel running surface. The third rail aims to deliver electrical power to the rolling stock through a collector shoe sliding along the rail. Due to inherent constraints of electrical sectioning, the third rail is not continuous throughout the whole line. At the air gaps, the ramps help the collector shoe to pass from one electrical section to another one. This is also the case with the turn-outs, as tracks are fed independently from eachother. In the following, a distinction is made between High-Speed (HS) ramps on the line and Low Speed (LS) ramps on the sidings, for instance of depots. 3 Excessive wear observed In November 2011, maintenance track patrol reported an excessive, undue wear on LS ramps, and, since January 2012, on HS ramps as well. The running surface was worn from 4.8mm down to 1,1mm in one year, with the specified limit being 1mm. This is in total contradiction with the theoretical life expectancy of 30 years for this sub-system. In total, 25% of the HS ramps on one line and 10% on the other are affected by this issue. It has been reported that the wear is more significant: • on the first line, which can be a consequence of the higher current on this line (1360A versus 960A per train) • on the entry ramps, as the current is higher in traction mode rather than in regenerative braking mode • on the HS ramps rather than LS ones, and more importantly on turn-out locations • when leaving the station, as the current during acceleration is high
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