Electrical testing lab

Every little helps

Nanotechnology could soon be making generators smaller and more efficient, reports E&T.

Nano-scale materials are infiltrating everyday society at a breathtaking rate, be it through anti-ageing cream, floor cleaner or the latest flash memory chip. However, the tiny particles are also making inroads into energy applications, where the results promise to be big.

In May this year, British researchers announced a £3m, European Union-funded project to develop 'radically innovative' electrical insulating tapes, based on nano-materials, for high-efficiency generators. Dubbed 'ANASTASIA', the 'advanced nano-structured tapes for electrotechnical high-power insulating applications' project aims to replace today's thick, semi-rigid insulating tapes with thinner, flexible versions. These would have a higher field-strength and better thermal stability.

As the researchers state: 'High-voltage insulating tape technology must be exploited. At a European-scale, a 0.2 per cent gain in generator conversion efficiency could save 1,000MW, nearly 10 fossil fuel plants.' And while a new insulating tape will not find its way into every generator across Europe, Professor Alun Vaughan, project leader at Southampton University, emphasises: 'You don't need to have a very significant increase in efficiency on a pan-European level, to make a difference.'

With this in mind, the Southampton team, along with academic and industrial partners including Nottingham Trent University, CEA, France, Politecnico di Torino, Italy, and Swiss tape maker Von Roll, are investigating different ways to fabricate the insulating material. Today's high voltage insulating tape is based on a glass-fibre carrier tape, co-laminated with mica paper impregnated by polymer resin. Wrapped around the copper bars of the stator, the tape protects them from partial discharges thanks to the mica, which acts as a wall against electrical erosion.

In the first of three approaches, the researchers will use existing polymer resins but instead of adding mica, will experiment with different combinations of nano-particles to see which produces the best results. Fabrication will be based on standard techniques and likely nano-particles include sheet-like silica, silica spheres, clay-type systems, boron nitride rods, as well as mica flakes.

'This is a lower risk strategy as we are using existing technologies, but to engineer the combination of properties that we want is quite tricky,' explains Vaughan. 'You might want to add silica to improve the breakdown behaviour, then a clay to improve erosion resistance to partial discharge activity and then perhaps add rod-like structures to improve thermal conductivity. This can be challenging but we know there are rewards to be had as people have demonstrated them already in the laboratory.'

The other two approaches are based on a sol-gel production route. This is a wet-chemical technique widely used in ceramic engineering in which a solution - the sol - acts as the precursor for a network - or gel - of particles.

As Vaughan explains, the second approach aims to grow the nano-particles, in-situ, within the epoxy resin, while the third, most ambitious, approach will see the resin replaced by a sol-gel matrix giving an all-inorganic system. Pursuing this production route bypasses the problem of aggregation, where nano-particles group together within the epoxy resin, reducing overall strength and thermal properties. What's more, the final approach promises unprecedented thermal properties.

'We're trying to develop tomorrow's technology using the first approach and then next week's and next month's with the sol-gel approaches,' says Vaughan. 'In around 18 months we will take a look at the viability of each and decide which technology will be used to produce a demonstrator stator bar.'

Industry-scale Tapes

Assuming the team of researchers produces a resin system with better thermal and electrical properties than today's structures, the next step will be to produce insulating tapes. However, will the improvements in the laboratory-fabricated resin system be transferable to an industry-scale insulation tape?

As Vaughan admits: 'Dispersing nanoparticles into the idealised laboratory resins is one thing. Dispersing them into the practical, really low viscosity resin systems used in industrial manufacture is another thing altogether.'

However, Vaughan and partners are confident they will fabricate a tape with a field strength some 40 per cent higher than current tapes. They also intend to boost thermal conduction by around 60 per cent while reducing tape thickness by 30 per cent, paving the way to more compact generator designs.

And once produced, the tape will be applied to a demonstrator stator bar, manufactured by Alstom. Engineers from the France-based energy business will test the bar to assess the performance of the insulation tape and investigate its impact on generator designs.

Ask Vaughan if the project researchers have a lot to achieve in three years and he says yes. However, he is sure they will get results.

'I am certain, at least with the first approach of nano-structuring the resins, that within three years we will be able to produce a material that can be impregnated to a tape, laid out onto a stator and tested,' he says. 'On the other hand, I don't believe that the concept of an all-inorganic insulation system will be viable in three years, but we will learn a lot from this work for subsequent projects.'

So how long until we see nano-materials in practice, saving energy? As the researchers set out to make the ultimate insulating tape, we're likely to see more everyday objects first, be they floor cleaners or anti-ageing creams. But while the benefits of some nano-products are debatable, the rewards from using nano-particles in high voltage insulating applications are definitely worth chasing.

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