Regenerative braking for direct-current locomotives

This paper gives a comparative study of several d-c., regenerative braking systems now in successful operation. The general characteristics of regenerative braking, including advantages, limitations and functions are briefly discussed. The principal points covered in the descriptions of the various systems are: method of field excitation during regeneration, compensation for sudden changes in line voltage or grade, method of control, operating characteristics and relative complication of equipment. Several systems are described in which the regenerating motor fields are excited by a separate generator provided for that purpose, and then other systems are described in which the fields are excited by one or more of the traction motors. Under the former heading are included C. M. & St. P. freight locomotive with a line driven motor-generator set for excitation, the Mexican locomotive with a dynamotor-driven, motor-generator set for excitation and the axle generator system. The applications described under the latter heading are the C. M. & St. P. gearless passenger, the Paulista and the Spanish Northern locomotives. A comparison is made of these two methods of field-excitation, based on a six-motor, two-speed, 3000 — volt locomotive. Curves are included illustrating the speed-braking characteristics and also the motoring characteristics. The conclusions drawn from this comparison are that, in general, the separate excitation system is to be preferred on account of the greater braking effort and greater speed range provided. Since the motor excitation system can be provided with less additional expense, it is desirable to consider this method when the expense of the separate excitation system does not seem justifiable.