Railway Overhead Contact Systems: First Paper: An Experimental Study of the Overhead Contact System for Electric Traction at 25 kV

Abstract

Increasing train speeds and the use of multiple pantographs have emphasized some of the problems of ensuring good current collection from the light overhead contact system used for railway electrification at 25 kV in Britain and overseas. The development, in Britain, of instrumentation and test methods is described, and the problems which arise as a result of ‘hard spots' and resonance effects are referred to. Experimental investigation has shown that greatly improved current collection can be obtained, by suitable modifications, even at speeds exceeding 100 mile/h, and under features such as bridges with minimum clearance. The main principle employed, which has been called ‘stiffness grading’, is to ensure a smooth transition of stiffness, or compliance of the overhead contact system through such features. These are, of necessity, considerably stiffer than normal open route equipment because of the strictly limited electrical clearances. The result is achieved primarily by modifications to the geometry of the equipment. It has been shown that such modifications can reduce appreciably the tendency of the system to build up oscillations of large amplitude, particularly in sequences of spans of approximately equal lengths. This tendency is much more marked where multiple pantographs are used, especially at certain spacings. Such phenomena can be remedied even more effectively by introduction of damping into the system and this can be achieved more conveniently by use of viscous dampers on the pantograph rather than on the overhead contact system. Appendix I describes recent test results which show that modified simple catenary equipment may be suitable for British Railways ‡ requirements if a smooth pantograph trajectory is ensured by suitable control of contact wire profile. This can be achieved by the use of mid-span sag. It will give an appreciable reduction of cost.