Insulation monitoring for aircraft electrical systems
Today’s large passenger aircraft rely on low-voltage distribution systems to power everything from the avionics and actuation to lighting and in-flight entertainment. However, with aircraft becoming increasingly electric, the need for higher voltages also increases. “With an increase in the predicted demand for high-voltage electrical power in large passenger aircraft and other more electric aircraft concepts, new electrical distribution systems will be required to enable safe, light, highly efficient electrical propulsion systems,” explains Antonio Griffo, a professor of Power Electronics and Electrical Drives at the University of Sheffield(opens in new window). But higher voltage means increased stresses to the electrical insulation of cables, electrical machines and components. It also means that monitoring the state of health of the insulation and detecting faults become crucial in safety-critical systems such as aircraft power systems. Enter the EU-funded IMITAES(opens in new window) project. The project, which received support from the Clean Sky 2 Joint Undertaking(opens in new window), has designed, demonstrated and supplied innovative insulation monitoring systems specifically based on the requirements of the aerospace sector.
Isolation Terra earthing
Whereas the power distribution systems found on most conventional aircraft use the aircraft’s metallic airframe as the earthing system, the electric aircraft of the future will require something a bit more robust. One alternative is Isolation Terra (IT) earthing. IT earthing configurations are characterised by having no intentional conductive connection to the Earth’s ground. An earthing system is a set of conductors and electrodes that provide a low-resistance path for electrical current to flow to the ground in the event of a fault or malfunction. In doing so, it helps ensure the safety of the passengers and crew and the continued functioning of the aircraft’s on-board equipment. “High-power electrical systems in high-reliability applications often utilise IT earthing, which offers such advantages as fault current management and continued operation post-fault,” says Griffo, who served as the IMITAES project coordinator. However, IT earthing also creates new challenges, including the ability to monitor and correctly determine when an insulation fault has occurred.
Monitoring IT earthing-based electrical systems
Despite the critically important role insulation monitoring technologies play in ensuring aircraft safety, by and large they have not been tested, proven, optimised or made commercially available for aerospace applications. That is until now. Thanks to the work done by the IMITAES project, such technology could soon be market ready. “We worked with Rolls Royce(opens in new window), a company dedicated to developing and delivering complex power and propulsion solutions for safety-critical aircraft applications, to understand the specific requirements of the aerospace sector,” notes Griffo. Based on these specifications, and together with Bender(opens in new window), a leading supplier of solutions for electrical safety, the project developed a number of models and prototypes for monitoring IT earthing-based electrical systems. Each solution has been verified and validated via an extensive set of experiments conducted in conditions representative of an aircraft power system.
Electrifying tomorrow’s aircraft today
The IMITAES team is currently working to further advance the technology readiness level of its monitoring solutions and prepare them for real-flight testing. They are also engaging with standardisation committees to ensure that their insulation monitoring devices become a standard feature on future aircraft. “All of this work will support the adoption of IT earthing systems and, ultimately, the further electrification of tomorrow’s aircraft,” concludes Griffo.