Small machine powers into transport

Generator breakthrough turbocharges machine into portable power and vehicle projects

By Sue Stuckey

A breakthrough in the evolution of electrical machines means that a small, highly efficient generator/motor nominated as the centrepiece of a 21st century hybrid electric car, has found a key role in a European research project to develop low emission public transport.

The 50kW version has a shaft that rotates at 60,000rpm – 10 times as fast as a car engine – enough to ensure that a conventional machine of similar output would break up under the high centrifugal forces.

It can be coupled directly to a small, high speed gas turbine, thus becoming a neat, lightweight, turbocharged, efficient, clean and inherently quiet generator of electricity.

The high speed breakthrough avoids the need for a large, expensive reduction gearbox between itself and the gas turbine used to drive it.

A genset based on the new technology with electronic controls weighs just 100kg compared with 1-2 tonnes for a conventional diesel generator producing the same power. Alone, the machine weighs just 9kg. The potential includes transport, cogeneration and portable power applications.

Professor Colin Besant, the machine’s inventor, forecasts a burgeoning market. With members of his team from Imperial College, London and commercial backers he has set up The Turbo Genset Company to promote and develop the technology working with gas turbine makers such as Turbomeca in France, Rolls-Royce US subsidiary Allison and PBS Czechoslovakia.

The high-speed breakthrough has been achieved using rare earth permanent magnets which rotate past a coil of copper wire to produce an electromagnetic field and generate electricity. Rotating at super-high speeds, the magnets are held in place by specially developed, immensely strong, carbon fibre rings.

Discs with their larger surface area replace the iron drum used for the core windings of a conventional generator/motor. Benefits include better heat dissipation improving the flow of electricity through circuit conductors.

Disc technology doubles fuel efficiency to around 95%. There is no hysteresis from stationary iron losses. With discs, the machine is modular and can be built up from several rotor and stator disc modules each able to produce 10kW power.

The machine is at the centre of two Government funded Brite-Euram projects to develop low emission vehicles.

The 50kW unit targets hybrid electric cars while the latest 100kW machine is part of an eco-friendly drive system that includes regenerative braking for larger vehicles like buses.

But it is in portable power generation projects that Besant sees the greatest potential for this machine which doubles as an electric motor delivering a 440V three-phase output suitable for industrial applications driving, say, turbo compressors or high-speed machine tool spindles.