The Stored Energy Technology Ltd. ‘Wheel-Motor’ based traction system is designed to significantly reduce costly power losses in the traction system by operating at much higher efficiencies over the whole load-speed range. The savings in losses are achieved in three ways:-

Firstly, the motor is direct drive, so all losses associated with a gearbox and drive shafts are eliminated, and as the motor operates at a lower speed than a conventional traction motor, windage and friction losses are much reduced.

Secondly, the motor is a permanent magnet synchronous machine, using high energy rare earth magnets, which means that no excitation losses occur.  Motor efficiencies in the region of 97% can be achieved, compared to typically 85% for an induction motor.

Thirdly, the use of 'Wheel-Motors' as a replacement of conventional drives will result in significant vehicle weight reduction.

The inclusion of the motor inside the wheel removes the need for the traditional motor-gearbox/driveshaft-axle arrangement, thus giving greater design flexibility and simplifying the provision of low floors in the bogie areas.

The motor control system monitors the speed of each individual Wheel-Motor very precisely and this simplifies the avoidance of wheel slip or slide.  Individually motored wheels are driven at relative speeds appropriate to the track curvature, thus virtually eliminating excessive tyre, flange and track wear caused by forced creep on moderate and sharp curves.  The lateral wheel set position within the gaugeway can also be monitored and contact between the wheel flange and the rail gauge corner minimised.

During braking, the S.E.T. Wheel-Motor can regenerate over the whole speed range down to a standstill.  Given that it is now possible to store very large amounts of energy on a vehicle directly as electrical energy in super capacitors it is practical to store energy released in regenerative braking, and reuse it to accelerate the vehicle later.  In this way it is possible with S.E.T. Wheel-Motors to recover a large proportion of the input traction energy in typical rapid transit duty cycles.

The use of on-board energy storage not only reduces the total power consumed, but smoothes out the peak demands.  Both of these effects mean that the size of the electrical infrastructure can be considerably reduced, or conversely that an old tramway system could be upgraded to rapid transit standards without the high expenditure involved in renewing electrical installations.  A secondary implication is that visual intrusion of overhead installations can be very much reduced. Indeed in very sensitive areas the overhead line can be dispensed with altogether and the stored energy could power the vehicle for short distances. These distances could be increased further if batteries are installed as part of the recovery system. Batteries are useful on hilly systems, as they have the capacity to store the energy released on downhill sections.

Typically, a light rail vehicle equipped with SET Wheel-Motors and an energy recovery system could save more than £100k in running costs over a 10 year period.

 Key points are:-

• Lighter, low floor vehicles

• Greatly reduced energy and maintenance costs

• Electrical braking enabled over the whole speed range, giving savings in brake wear

• More precise control giving the possibility of incorporating better wheelslip/slide protection, allowing better traction under adverse rail conditions.

Four Wheel-Motors and the SET control system have been fitted in a converted tram, which was test run on the  Blackpool  tramway  in  early 2009.  The  tram covered more than 2000km and showed significant energy savings compared to traditional trams