Hybrid Technology for railroads June 22nd, 2007
From Modern Railways with Comments added by RailPAC President, Paul Dyson
The following is an extract from the June 2007 edition of Modern Railways, the leading UK railway magazine. It was written by Roger Ford, a former traction engineer with the English Electric Company, and now technical editor of MR. It is reproduced with his and the magazineâ€™s permission.
Given the extraordinary capital cost of electrification, not to mention visual intrusion, safety issues, and energy consumed in mining and producing all that copper, aluminum, steel and other metals, Iâ€™ve always hoped that hybrid technology could be applied to railroad traction for a more cost effective solution.
For those not familiar with the terms, a class 43 is the power car of BRâ€™s intercity 125 diesel train, and Mark 3 coaches are the trailer cars that operate therewith. Porterbrook is a UK rolling stock leasing company. Hayabusa is Japanese for peregrine falcon. The Brush company has traditionally used the names of birds of prey for its prototypes.
Mr. Ford writes:
Long experience tells me it is prudent to be sceptical about new technology. So I went off to Loughborough to see Porterbrookâ€™s â€˜newâ€™ Hitachi/Brush hybrid Class 43 IC125 power car with some hard questions and some hard numbers to back them up. On the way I ran a quick spread sheet to get a feel for the numbers involved. I made the kinetic energy of a 70-tonne Class 43 at 125mph around 20 kWh. The ability of the hybrid system to recover and store this energy when braking would be my test case.
What Hitachi and Brush have done is to install the Lithium-ion battery, supplied by Hitachi Vehicle Energy Ltd., in a Mk 3 trailer guard second (TGS) which is coupled to the power car. The Class 43 has been fitted with new Hitachi alternating current traction motors rated at 300kW each.
Power to the traction motors is provided by inverters mounted underneath the TGS. The inverters can be supplied from the battery, the existing alternator on the power carâ€™s diesel engine, or both.
Hybrid technology stands or falls on the battery. On this prototype it is assembled from modules, each with a capacity of 1kWh and weighing 20kg. With 48 modules the battery has a total capacity of 48kWh and weighs 960kg (2115 pounds). Specific capacity is thus 50kWh/tonne (metric ton) â€“ the current benchmark for Lithium-ion.
That said, Hitachi is keen to point out that battery technology is developing rapidly with significant reductions in weight and increases in storage capacity, driven by the demands of the automotive industry. But I didnâ€™t get an answer when I asked the hybridâ€™s battery cost.
So the 960kg battery is more than capable of storing the energy regenerated when braking the Class 43 electrically from maximum speed to standstill. What about reusing the recovered energy? The peak power output is an impressive 1MegaWatt or 1,350hp.
For comparison, the Class 43â€™s diesel prime mover has a rating of 1.68MW (2,250hp). However, the off-the-shelf traction motors have derated the hybrid to 1.2MW for traction at the wheels.
With these ratings and a fully charged battery, the power car could accelerate away at around 80% of the traction motorsâ€™ full power for around 170 seconds. A couple of stops from 125mph would then recharge the battery.
And to see a 2 power cars plus three formation zip away silently like an EMU and then return at speed got everyoneâ€™s attention. As English Electric (and EMD!) knew â€“ to sell something new build a demonstrator.
There is a limit to the rate at which the hybridâ€™s battery can be charged. But if it canâ€™t accept all the braking energy, the surplus is dissipated in resistors as with rheostatic braking (dynamic braking, PD). Trial running to date indicates that the battery can store most of the energy generated in the equivalent of notch 2 braking.
Another issue to be explored is the relationship between battery life and capacity. Experience with hybrid cars suggests that battery life is maximized when the battery is kept charged to between 20% and 60% of its capacity.
Clearly, using that 1MW for long periods could shorten the battery life. And while Hitachi is coy on the cost of the tonne of battery, it wonâ€™t be cheap and you want it to last. But even staying within the optimum life charging zone the hybrid power car will be able to brake its own weight and enable the prototype train to arrive and depart at terminal stations without the engines running.
Of course Hayabusa is not a perpetual motion machine. According to Hitachi Transportation Systems project engineer, the internal losses of the battery mean that charging and discharging are each around 90% efficient, so only 80% of the regenerated energy is available for traction.
Initial estimates are that fuel saving with the hybrid system in operation will be of the order of 20%, similar to an electric train regenerating into the overhead line. But in a production hybrid the overall savings would be even greater.
First, the hybrid control system can blend in the battery power under acceleration so that instead of the diesel engine working at full power the engine management system keeps it at the point on the power/speed curve for optimum fuel consumption.
Second, with battery boost, the diesel engine can be made smaller, which means that the cooler group can be smaller and lighter and the train can carry less fuel. The benefits should more than outweigh the extra mass of the battery.
Paul Dyson adds:
The large fleet of DMU vehicles in Europe, especially the UK, presents a ready market for this technology. The much heavier weight of US rail equipment, built to meet what many maintain are out of date FRA standards, presents more of a problem, although it should not be insurmountable. As Mr. Ford says, pushed by a demand for fuel saving highway vehicles, battery performance is improving all the time.
While I remain a proponent of electrification, itâ€™s hard to see where the capital will come from for track improvements, rolling stock and signaling for new services AND stringing up catenary. The USA needs to consider the option of hybrid diesel technology; it may be the answer for our next generation of trains.
Hitachi has three hybrid DEMUs entering service in Japan. How about a demonstrator for California?