„Non-receptive“ catenary
Main barrier for the use of regenerative braking is the fact that the supply
system is often „non-receptive“, i.e. it does not accept the recovered energy
because there is no other train close enough to use it. However, this problem
arises in 16,7 Hz systems only rarely due to the reasons laid out in
Description.
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. |