International Railway Journal - May 2008 - (Page 42B)

motor modifications An unmodified stator showing damaged sections (left) and a modified stator frame after repair. Standards Organisation (RDSO) studied various design practices followed by leading traction motor manufacturers. For all types of three-phase traction motors in mainline operation, coil overhangs on both sides of stators are supported with fibre-reinforced plastic (FRP) rings, which in turn are anchored to stator lamination stack end plates with six to eight clamps by most of the manufacturers. This type of support arrangement is available for coil overhang lengths above 100mm irrespective of the type of suspension arrangement of the traction motors. Typically for this traction motor, with a core length of 480mm, the length of coil overhang on the nondrive end (NDE) side is 167mm, and on drive end (DE) side it is 135mm. The mass of the overhang on the NDE side is approximately 38kg, whereas on the DE side, it is 35kg. After the study of available designs of stators, failure data, and trial reports, an unsupported mass of 38kg with longer length of overhangs is said to be the main cause of insulation and brazed joint failures in the stators. Support design The main challenge RDSO faced was to develop a suitable design for supporting coil overhangs as it was not possible to minimise the shocks and vibration on the existing axle-hung nose-suspended traction motors. Redesigning the traction motors and suspension arrangement could have been expensive and at the same time it was equally essential to address the problems of the existing 1200 traction motors in an economical manner. The support arrangement commonly followed by leading traction motor manufacturers could not be adopted in these motors because of space constraints. Coil overhangs in these stators project radially outwards, leaving no space on end plates of stator stacks for standard supports. Since the support arrangement was never envisaged by designers, they didn’t design the coil windings accordingly. Re-designing of coils to reduce the length of overhangs for a power rating of 850kW or to change its profile was also not possible in the existing envelope of the stator frame. The only option left was to use the available space in the stators for the suitable support of the coil overhangs. IR tried all manner of ways of providing support to the coil overhangs in the available space and finalised a supporting scheme after examining its feasibility of implementation and validation by finite element analysis (FEA) at the Indian Institute of Technology, Kanpur. FEA results revealed total elimination of stresses at coil overhangs and core slot ends in this scheme. Apart from supporting the overhang, better insulation and improvement in manufacturing practices have also been adopted. To tackle the problem of temperature sensors, better insulation was provided along with a revised potting compound. The mounting arrangement of the temperature sensor was modified to eliminate the need to lift the locomotive’s body to replace it. All stators taken for rewinding are being modified with this scheme. This scheme has also been adopted in the current manufacturing of stators. The next challenge was to incorporate the standard support arrangement followed by all traction motor manufacturers in the existing design of stators. Without changing the design of stator, the support arrangement has been incorporated by modifying the end fittings of motors for future manufacturing as a long-term measure. The prototype of such stators has been developed and IR will manufacture all new stators with new design. The cost of the modification in one stator is just $US 200. This modification will save $US 10.2 million a year on maintenance, and billions of dollars of revenue could be saved from the release of track capacity by eliminating midsection failures. This reliability improvement measure of traction motors is a major step towards augmenting the line capacity of IR to meet burgeoning economic growth that IR is witnessing. IRJ The author would like to thank H S Pannu of RDSO, Sudesh Kumar, of the Railway Board and Mahesh Chand of IR, for their assistance with this article. IRJ May 2008 42BB

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International Railway Journal - May 2008 Contents This Month News Transit News Market News Technology News News Analysis Italian Railways on the Road to Recovery High-Speed: On the Home Straight Korea Develops High-Speed Ambitions Setting New Standards for New Rolling Stock India Solves Traction Motor Conundrum Weathering the Storm with Climatic Testing Technology Drives US Train Inspections Rendezvous Full Contact List Advertisers Index The Last Word

International Railway Journal - May 2008

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