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The Advanced Electric Machine Technologies for Aircraft (AEMTA) Research & Technology programme, part-funded by Innovate UK, was created to re-establish and further develop electric machine design capability at Safran Electrical & Power UK. The programme included a large number of different technology strands, including high-temperature wire insulation. Naveed Sheikh, Safran Electrical & Power UK

Research & Technology Programme Manager, explained the rationale for the AEMTA programme: “The increasing electrification of functions on board aircraft is a formative and irreversible change that will move faster and intensify with future programmes. Hydraulic and pneumatic power is gradually being replaced by electricity. This has many advantages, both in terms of safety and the environment. We wanted to develop technologies to facilitate More Electric Aircraft (MEA) and establish a future UK supply chain for their commercial exploitation. “Teesside University’s role was to create

❱ ❱ Electrical and hybrid power will become the aircraft propulsion norm for future generations

that could survive such extreme temperatures. For windings that are to be used in such

hostile environments, Hodgson explains that the use of organic materials is not an option. The university team therefore looked at the use of ceramics. However, although such materials have the required thermal properties, they are mechanically poor. For this reason, Hodgson’s team developed a ceramic composite. • Ceramic composite insulation Teesside university overcame the problem of ceramic rigidity by creating a composite from ceramic and polymer at the nano-scale. Mixing the materials at such a tiny scale creates a ceramic matrix with finely distributed organic material, which provides flexibility for winding. Once it is wound, curing the winding “burns off” the organic material leaving just the matrix. The voids are so tiny that the ceramic settles into them, leaving a fully insulating coating.

novel technologies required to produce the high performance, robust and lightweight electrical machines used in the MEA – particularly the electrical insulation materials which are one of the key performance limiting factors in these systems. We had problems where wire is used in high temperatures. The insulation would break down and we needed enhanced capability in this technology. Professor Hodgson and his team successfully developed coatings to protect the wire and enabled it to perform at temperatures which met our needs.”

This hard ceramic insulation has sufficient remaining flexibility for thermal expansion and contraction without being compromised.

MORE MOTORS, MORE POWER The second challenge faced by Professor Hodgson and his team was to enable higher power density motors that could be distributed throughout the highly electrified aircraft of the future. The replacement of many hydraulic and pneumatic systems with electrical systems is more energy efficient and saves weight but places a requirement on more motors, which are smaller and more powerful. According to Hodgson, in this scenario, insulation is the most usual point of failure and so one solution was to use more exotic polymers but this has a significant cost penalty. Instead, his team examined the ways in which the polymer fails.

“When a polymer is heated, the chains become more mobile, opening oxygen diffusing gaps and eventually disintegrating,” he tells me. The answer that Teesside University came up with was to add molecular scale ceramic to link the polymer chains together. This successfully stopped the oxidisation of the polymer and took the temperature resistance up by 40°C, a significant step in terms of operational life expectancy. • Additive manufacturing An advantage of creating this polymer / ceramic mix is that it lends itself to additive manufacturing using the precursor chemicals. Additive manufacturing also has the

benefit that it overcomes some of the repeatability issues of existing techniques. “The winding becomes less of a birds-nest of wires and more of a repeatably manufactured structure,” Hodgson concludes. n

Aerospace Test & Validation 2018 /// 3


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