Principle

Modern diesel-electric vehicles with 3-phase traction motors can be braked dynamically by using the electric traction motors as generators. This capacity is usually exploited in order to have a wear-free braking mode. The control of the traction system can be designed in such a way that part of the recovered energy can be used to feed on-board consumers.

Technical details

In modern diesel-electric 3-phase locomotives the Diesel engine drives a generator feeding the DC link. The DC link feeds the traction inverters as well as the auxiliaries and the train bus supply. During braking, the traction motors feed the recovered power into the DC link. This additional power can either be converted into heat in braking resistors or used for other consumers, namely auxiliaries (compressors, ventilation etc.) or the train bus supply (supplying the comfort functions in passenger trains).The power management is usually realised as follows: The recovered braking power is fed into the DC link. The part of this power that can be used for auxiliaries or train bus supply is drawn from the DC link, the rest is dissipated in the resistors. The resistor is automatically "switched on" if the voltage in the DC link exceeds a certain limit value.

There are no data available on the in-use energy savings realised by the ÖBB 2016 locomotives.

In order to make an estimate of the potential, on has to look at the power management and the layout of the locomotive: The motors have a traction power of 1600 kW and a braking power of 1000 kW. If maximum braking power is applied, these 1000 kW are fed into the DC link. The part of this power that can be used for auxiliaries or train bus supply is drawn from the DC link, the rest is dissipated in the resistors. The resistor is automatically "switched on" if the voltage in the DC link exceeds a certain limit. The maximum power intake of auxiliaries is about 50 kW. In passenger operation, there is an additional ~ 460 kW maximum power drawn by the train bus supply for comfort functions, mainly coach heating.

These data allow for a rough estimate of the energy saving potential in freight and passenger trains.

Locomotives in freight operation

A maximum of ~5% of the recovered energy can be used on board. In addition, the potential for regenerative braking in freight operation is low (< 5%). Therefore the energy efficiency potential through the use of brake energy for auxiliary functions is almost negligible.

Locomotives in passenger operation

A maximum ~50% of the recovered braking power is consumed by on-board functions (auxiliaries comfort functions). This is however only the case in long passenger trains in winter. Usually the potential will be lower. An average of 20% could be realistic. In view of the potential for regenerative braking between about 15 % (main lines) and 35% (regional lines), the overall saving potential is between 3 and 7%. However, this is still very optimistic since it is based on the assumption that the dynamic brakes are used exclusively. In real operation, energy savings of 2% in main line and 5 % in regional line operation seems realistic.

DMUs

There is no data available on the use of recovered braking energy for comfort functions in DMUs. In modern diesel-electric stock using 3-phase traction equipment, there should be no principal barriers.