• Energy saving
• Reduced wear of mechanical brakes.

Wear on mechanical brakes

The use of regenerative brakes reduces wear and maintenance of the mechanical brakes. It may also be possible to reduce the complexity, weight and cost of the mechanical brakes.

Since regenerative braking works without friction, no wearing parts are present.

Feeding sections and „non-receptive“ catenary

Catenary voltage (25 kV) is very high which allows for a transmission at low losses over relatively big distances. Since they share a common frequency, 25 kV 50 Hz systems receive their power supply directly from the public grid. The primary power supply is therefore taken from different points without any connection between the points resulting in different phases in the network. As a consequence, the feeding sections have to be electrically separated to avoid short circuits. This lack of interconnection strongly reduces the probability of having two trains (one braking while the other one is in traction).

Insufficient braking power

The power of regenerative brakes is roughly the same as the one installed for traction. For many situations (trains running late, bad track conditions, unexpected stop signals) this is not sufficient. In this case regenerative brakes are blended with dissipative brakes or completely replaced by them.

Generally, EMUs have a better regenerative braking performance than loco-hauled trains, since more axles are powered. The higher the motor power and the more axles are powered, the more energy may be recovered.

In the case of heavy freight trains only a small fraction of the kinetic energy can be recovered, since tractive force is supplied only by the locomotive and (mechanical) braking force is distributed along the entire train. The situation is somewhat improved in double traction, i.e. with a train hauled by two locomotives.

In loco-hauled stock, there is a general limitation to the braking of the locomotive. If the locomotive brakes, the following cars exert a longitudinal force on the rear of the locomotive. In order to avoid an increased derailment risk, this force must not exceed a certain limit. Especially in freight trains this is a strong limitation for the braking performance of the locomotive and thus for regenerative braking.

Running time

Regenerative braking slightly prolongs running time compared to trains using mechanical brakes. This effect is small, but may lead to the use of mechanical brakes (or blending) in case of tight running schedules.

Acceptance

Acceptance is generally high. However some drivers are reported to be reluctant to use regenerative brakes because of safety or timetable concerns.

Operation concept of the locomotive

Operation concept of the driver cabin may not be optimised for the use of regenerative braking. For example, in most locomotives at DB the brake handles are usually coupled for blended braking. For an exclusive use of electric braking, an extra effort is required to decouple the handles.

The future potential may be exploited by removing some of the present obstacles. This includes

• Training programs and incentives
• Favourable operational concepts for driver cabins of locomotives: Manual braking concepts should be optimised in order to facilitate electric braking whenever feasible. On the other hand, electronic control of brake blending is to be preferred generally. This way the maximum permitted use of recuperation brakes can be ensured.
• Installation of more high-powered traction systems (which will be too expensive in most cases)
• Migration towards EMUs

However, the main obstacle for regenerative braking in 50 Hz systems which is the electric separation of feeding section cannot be eliminated.