Turbo Genset on trial

21 July 2000

BP Exploration has signed an agreement with Turbo Genset, makers of a radical design of compact high speed generator, to run trials of two prototype units at its Wytch Farm (Dorset, UK) onshore oil site. For what is called an “extended trial period” the natural gas powered generators will export low cost “environmentally friendly” electricity from one of the well sites; the trials will assess the suitability of the generators for further applications in the oil and gas industry.

Low weight compact unit

The turbo genset is a small scale electrical power generator which uses a gas turbine engine as the prime mover directly coupled to a high speed permanent magnet alternator. The technology is currently being further developed at Imperial College, London. The company’s innovation is a high speed, highly compact alternator directly powered by a small gas turbine using various fuels, including natural gas. A turbo genset that can produce 50kW weighs only 100 kg compared to 1-2 tonne for a conventional genset. The company is also developing a 100kW unit, with output powers ultimately reaching 1 MW. Claimed advantages over conventional units are compactness, reliability, low noxious emissions, low manufacturing cost, low installation cost, low maintenance, multi-fuel capability, and high grade exhaust heat.

  The key feature of the alternator developed by the company is its high operating speed. Because it is capable of operating at the same speed as the gas turbine engine, the engine shaft can be coupled directly to the alternator without the need for a reduction gearbox. This further improves the power-to-weight ratio and reliability of the overall system.

Patented disc rotor

The TGC alternator adopts a patented disc configuration in which the magnetic field is axial. High-speed alternators have only become feasible with the advent of high-field strength rare-earth magnetic materials such as Neodymium-Iron-Boron and Samarium-Cobalt. Because these materials tend to be very brittle and have poor tensile strength, they need to be supported by a high-strength retainment shell under the extreme centrifugal loads experienced at high speeds.

  The rotor consists of two or more discs which share the same shaft and contain the permanent magnets, while the stator consists of one or more discs which contain the windings, each rotor/stator presently producing about 10 kW of electrical output. The 50 kW alternator that will feature in the company’s first commercial turbo gensets will contain 5 stator discs connected in series and 6 rotor discs sharing the same shaft. The device is roughly the same size as a car alternator, but produces over 50 times the electrical power.

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