Braking and energy recovery

Its job in the system

Every station stop requires the train’s motion to be reduced in a controlled way. Braking is therefore part of both the journey’s timing and its energy balance. A train approaching a platform needs a suitable stopping profile, while the signalling system must protect enough space for the movement. Recovering energy is valuable, but safe stopping remains the purpose.

How it works

With regenerative braking, suitable traction motors operate as generators during deceleration. Some kinetic energy becomes electrical energy rather than being dissipated as heat. The energy needs somewhere to go: another receptive train, suitable storage, or electrical equipment able to return it to another supply. Regeneration is a transfer with losses, not a source of new energy.

If the electrical network cannot accept all the available energy, other braking arrangements are needed. Friction brakes remain important, and some trains dissipate electrical braking energy in resistors. The combination varies with vehicle design and operating conditions. A diagram showing energy returning to a wire should therefore not imply that every stop returns all its energy to the public grid.

What it connects to

The useful recovery depends on the train and the wider traction system. Another train accelerating nearby can be a recipient, while compatible substation equipment can expand the available destinations. Service patterns, line conditions and electrical design affect the result. A greener train and a receptive power network are complementary investments.

Different places, different designs

Network Rail describes regeneration to its third-rail system when another train can take the energy. A London Assembly answer describes inverters that can feed otherwise unused braking energy into other Tube power supplies. These are specific arrangements. This resource does not assign a universal recovery percentage, because the destination and losses differ.