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   Kinetic Energy Storage System (KESS)  not evaluated  

Manufacturer / Railway company:
Urenco Power Technologies Ltd.

The heart of the system is a 'self balancing' carbon and glass fibre cylindrical composite rotor, mounted on unique maintenance-free bearings.The bore of the rotor is lined with a magnetic loaded composite and forms the rotor of an integral motor/generator. The design can be configured to give power outputs up to 250kW without modification other than a change to the rotor magnetisation pattern. It has design life of up to 10 million charging and discharging cycles and is designed to be maintenance free. It operates in a vacuum with mechanical losses of only 138 watts - all other losses being electrical. It is modular in construction, standing approximately 1.2 metres high with a footprint of 600mm x 600mm. The power electronics consist of a standard bi-directional IGBT based switching system with suitable developed control software. It has an extremely fast response time, changing from coasting to full power discharge in less than 3 milliseconds. The system can be tailored to suit applications by group mounting of standard units and is compatible with most AC and DC traction applications.

Advantage for energy efficiency:
Recover braking energy! Regenerative trains are able to feed braking energy into the line. However, if there is no load to absorb this, i.e. a conveniently placed accelerating train, the energy is dissipated as heat onboard the train.The provision of a trackside energy store would mean that the energy can always be absorbed and then returned tothe system when a train accelerates. The ideal characteristics for a traction energy storage system can be estimated from consideration of the following parameters. i) The energy stored in the trains as kinetic energy (MJ) ii) The acceleration and deceleration rates iii) The proportion of the train’s energy transmitted to another train iv) The frequency of the trains v) Topography of the line (i.e. up or down hill and level differences) vi) The train’s mass This is obviously only a first order estimate and detailed modelling of a particular system would be needed to confirm precisely the size and benefits that can be derived - but it is sufficient to classify the energy storage system requirements and hence rank the various technologies available. This is best illustrated by way of an example:- Consider a metro train which has the following characteristics:- i) Energy stored in the train prior to commencement of braking 30MJs ii) Energy required to accelerate train to cruising speed 40MJs iii) Acceleration time 30 seconds iv) Deceleration time 20 seconds v) Train frequency 20 per hour vi) Percentage of braking energy transmitted to other trains on the system 30%. vii) No allowance is made for Potential Energy stored due to altitude. The minimum energy exchange capability required of the energy storage system is given by the product of the number of train stops and starts per hour, the proportion of the trains energy absorbed by other trains, the kinetic energy stored in the train at the point it starts to brake minus the difference in potential energy between the point at which the train starts to brake and the point at which it has actually stopped. 30 x 20 x 2 (1-0.3) = 840MJ/hr The energy storage capacity needed is the energy exchanged per train stop minus the energy transmitted to other trains on the system. 30(1-0.3) = 21MJ - per stop/start event The average power ratings of the energy storage system required to receive and transmit the energy recovered are:- Braking 21MJ/ 20 s = 1.05MW Accelerating 21MJ/30 s = 0.7 MW To give an adequate life, the system must be capable of at least 106 to 107 cycles and in order to limit the formation of voltage and current spikes, a very fast response time in changing from charging to discharging is required.

Availability / Level of development:
The UPT KESS system is commercially available and installed in a number of applications around the world.

For further information please contact Urenco Power Technologies at

References / Links:  UPT website
Related projects:
Contact persons:  Kasper Pors Hansen (Urenco Power Technologies)
 date created: 2004-04-16
© UIC - International Union of Railways 2003
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