Flywheels offer cheap option for operating trams
EVEN AS Calcutta's transport authorities plan to phase out the tram, it is making a comeback in other parts of the world as technology's solution for a low-cost, non-polluting urban transport system.
British firm JPM Parry and Associates has developed a modern tramway system, which does not require overhead wires that besides being expensive to install and maintain, are ugly and vulnerable to theft. The motive power for the new tram system comes from a flywheel, a disc on a revolving shaft that can accumulate power, which is mounted horizontally below the tram's floor.
The 250-kg flywheel can be electrically charged at each tram-stop and the present model, which has a capacity of 25 passengers, can cover a distance of 4 km on one charge. Complete recharging of the flywheel takes 90 seconds, but if the charging is done at smaller intervals, when the energy stored in the flywheel is not totally exhausted, it can be done faster. The manufacturers claim that in practice, there will be no delays because of this limitation (Electrotechnology, Vol 4, No 2).
Parry's most important innovation was the use of direct mechanical transmission of power from the flywheel to the rail wheels. Earlier flywheel systems transferred power through generators and electric motors, which resulted in power wastage. Mechanical transfer of power also allows braking energy to be fed back to the flywheel, instead of being dissipated as heat.
The tram will carry a small battery for emergency power and for ancillary equipment such as lights, horn and wipers. It will run at a maximum speed of 56 kmph.
The cost of such a tram system, including hardware, design and commissioning, will start at about L90,000, which is a fraction of what electrically run alternative transport systems.