外文翻译(交流电气化铁路牵引系统)课稿.doc

Abstract Increasing attention has been shown in recent years in the a.c. electrification of railway traction systems and a number of established systems now exist throughout the world. Where the traction system is supplied directly from a high-voltage national-grid network, a common component of such schemes is a step down transformer connection between the two systems. The electrical, mechanical and thermal design of these transformers is subject to a number of special considerations not normally encountered in the design of distribution-type transformers of similar rating and voltage class. The paper reviews the operating conditions peculiar to railway traction such as over voltages, short circuits, cyclic and peak loadings and discusses how these conditions influence the design and construction of single-phase transformers supplying power for traction purposes. The paper describes the engineering practice and operating experience obtained with the British 25 kV a.c. railway-traction system in particular, but much of the system and transformer-design philosophy and operational experience referred to applies to a.c. traction systems elsewhere in the world. Key Words: Power transformers, Railways, Traction 1 Introduction In March 1956 the British Transport Commission announced their intention to adopt a 25 kV single-phase 50 Hz a.c. system as the standard for future electrification of British Railways in all Regions except the Southern, where extension of the existing third-rail system, which had been operating satisfactorily for some years, was considered to be the most satisfactory course to follow. The commission had earlier authorized a study to be made of the comparative costs of electrification at 1500 V d.c. and at 25 000 V single-phase 50 Hz a.c. This showed both economic and technical advantages in favor of the a.c. system, and the decision was taken to adopt it. Another decisive factor was the successful operational experience gained by the French Rai