TRIBRID Transmission Comprising Compressed Air, Flywheels and Batteries
Intended for lightly used routes or for localities where it would not be economic to electrify the line, the PPM TRIBRID affordable trains will deliver the benefits of electrification by means of CAES – Compressed Air Energy Storage. The TRIBRID traction bogies, though regarded as innovative, are actually an amalgamation of two well tried and tested engineering arrangements; PPM’s Class 139 hybrid primary driveline with over 10 years in exemplary service on the UK’s national rail network, and Clayton Equipment’s commercially-established hybrid battery electric locomotives. The power from the traction batteries is supplemented by additional power from the PPM flywheel energy store. Everything is accommodated within the traction car’s bogies, except for compressed air tanks which are located centrally under the carriage floor. Clayton are the manufacturer.
Amalgamating two successful hybrids creates a Tribrid. The prime mover air motor of the Tribrid vehicle drives a flywheel which accumulates kinetic energy which is linked to an electricity generator providing traction current at a steady rate or in surges to accelerate the vehicle. When cruising at a steady speed the current maintains the momentum of the train and at the same time feeds energy to a pack of high charge batteries. These can be accommodated with space available in the carriage body, but more conveniently in a second bogie, which in most applications will not need to carry traction equipment and has space available. The Tribrid arrangement improves energy efficiency in two different ways: –
- At times when the vehicle is descending gradients and slowing down approaching a station it is not necessary to apply the brakes as the energy flow to the wheel’s reverses, returning charge to the batteries. When hydrostatic secondary drivelines are used (as in the Class 139s) this accelerates the flywheel, recovering kinetic energy;
- Because the prime mover motor is far smaller than in a non-hybrid vehicle its energy consumption is lower, and needing less space is easier to fit in a bogie.
Compressed Air – Helping the Environment
There is no shortage of natural energy, but ever since the Industrial Revolution engineers have tended to favour the use of coal and oil because they are available in concentrated forms, easy to carry in a moving vehicle and are simple to contain and store until required. Wind energy cannot be turned on and off and solar energy, while more predictable, is most available when it is least needed, at midday in mid-summer. Modern wind turbines and photo voltaic arrays can drive air compressors and put solar and wind energy into store. In the Tribrid concept vehicle this can be carried on board. The biggest difference between a) batteries and b) CAES is that the recharging of the former is done from mains supply which is being generated, not drawn from storage. CAES can be stored in bulk quite cheaply and can be piped across to the vehicle very quickly at any time from a trackside store.
Parry People Movers Ltd, Overend Road, Cradley Heath, West Midlands, B64 7DD
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