• Energy saving
• Reduced wear of mechanical brakes.

Wear of mechanical brakes

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

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

Low voltage

Due to the low catenary voltage in DC systems (1,5 or 3 kV) transmission losses are high. This reduces the probability of having trains braking and trains accelerating close enough to each other to allow for an effective transmission considerably. Without additional technology to improve the situation, substantial recovery rates can only be achieved in dense suburban networks.

Voltage limits

It may happen that during braking the catenary voltage increases beyond the limits foreseen by the standards. In this case voltage is automatically cut off and no recovery is possible.

Feedback into supply grid

A feedback of recovered energy into the public grid is usually not an option in DC systems. However, if substations are equipped with thyristor inverter units , they become reversible and can feed energy into the supply grid.

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.

Acceptance

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

Inverter units for substations

By installing thyristor inverters in substations of DC systems, a feeding back of recovered braking energy into the public mains becomes a possibility. This can considerably increase recuperation rates in suburban or regional DC systems.

Energy storage

On-board or stationary energy storage are another way of enhancing recuperation rates in DC systems.

Automatic train control

Automatic driver-less systems offer the possibility of introducing a timetable which is optimised for regenerative braking by synchronising the acceleration and braking phases of subsequent trains.