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ELECTRIC AVIATION Insulating the core of electric


Jonathan Newell talks to Professor Simon Hodgson of Teesside University about pumping up the power for electric aviation without burning out the motors.


H


ybrid and electric power could be the future for cleaner, greener aviation and all the major engine manufacturers are


developing the technology that will keep them competitive in the future era of electric aircraft. However, such development isn’t without its challenges. One significant challenge is ensuring


that electric motor windings can endure the rigours of extreme environments. To find out more about this, I spoke to Professor Simon Hodgson, Pro Vice- Chancellor (Research and Innovation) at Teesside University, whose team is working on high-temperature wire insulation technology for the aviation industry. The work undertaken at Teesside has so far been of benefit to two aviation giants, Rolls-Royce and Safran Electrical & Power UK, each of which has interests in very different applications.


LIMITATIONS ON INSULATION A constraint that has always existed with motor windings has been the heat resistance of the insulation and until now, the industry hasn’t made any massive leaps and bounds in development. The windings of a century ago were


insulated with Shellac and could withstand temperatures of no more than 150-170°C before failing. Since that time, motors have typically seen an increase of 5-10°C every decade. The move to man-made polymer insulation led to improvements resulting in the current resistance levels of 220-240°C. According to Hodgson, this is a key design limitation on producing reliable, high power motors. “As the power of the motor increases, it reaches the limit of the insulation causing failure over time. A rule of thumb is that the motor life can halve for every 10°C of over-heating,” he says.


2 /// Aerospace Test & Validation 2018


❱ ❱ Professor Simon Hodgson sees ceramics and nano-technology as the answer to overcoming environmental factors in motor winding insulation failures


HEAT SOURCES Teesside is approaching the challenge based on the fact that there are two significant sources of heat that the motor is exposed to. There is internally generated heat, which can be considerable and hard to model and there is environmental heat. • Internal heat Temperature patterns within the windings can be very variable and can be a simple function of the amount of electrical energy or it can be more complex based on localised winding densities, which are harder to model and can vary considerably with manufacturing methods. If such localised heat sources are located near to a heat sink, they present less of a problem. Traditionally, to overcome the possibility of hot-spots, motors tend to be over-specified. This itself causes a problem in weight sensitive aerospace applications. • Environmental heat The main challenge associated with environmental heat is the need to use embedded motors in hybrid powertrains, where the motors will be exposed to the extreme heat generated by the engine in which they’re located.


MOTORS IN HYBRID AERO ENGINES Rolls-Royce’s Future Technologies Group is engaged in a major push to make step changes around engine development with moves towards hybrid propulsion combing gas turbine, generator and electrical propulsion motors.


According to Alexis Lambourne, a


Novel Materials Specialist at Rolls- Royce, a key enabling technology for an aerospace hybrid propulsion package comes from the ability to integrate electrical systems into the core of a gas turbine. “Our need was to demonstrate high-temperature electrical wire insulation technology capable of operating at 450°C, thereby enabling this technology to go into electrical motors that would be used in a gas turbine engine,” Lambourne explains. Teesside University provided the high


temperature wire, and wire encapsulation through their coatings,


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