Regenerative Braking

an electric braking system for modes of transportation operated by electricity, for instance, electric trains and streetcars, or for industrial electric drives. Electrical energy is regenerated, or balanced, by converting the mechanical energy of the transportation system or electric drive into electrical energy, which is returned to the power line.

Regenerative braking is based on the reversibility of electrical machines. During regenerative braking a traction motor operates as a generator and creates the necessary drag torque on the shaft, which provides for the braking of the drive system. Electrical energy is produced by a motor-generator either from the potential energy of the electric transportation system as it moves down a grade at a constant speed or from the kinetic energy produced as the drive system is decelerated. Regenerative braking represents a considerable saving in electrical energy. It is most effective on larger modes of transportation, for example, on electric locomotives that operate on main lines, on suburban electric trains, and on modern trolleybuses.

A regenerative braking system must meet a number of special requirements because only generators with dropping external characteristics can be used. Therefore, traction motors with series excitation are switched over to separate excitation for regenerative braking.