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Assessment of arc tracking hazards in high voltage aerospace systems

Periodic Reporting for period 2 - ARCTRACK (Assessment of arc tracking hazards in high voltage aerospace systems)

Reporting period: 2021-04-01 to 2022-03-31

As we develop hybrid and all electric aircraft, the voltage level of the onboard electrical systems is expected to climb to 0.75-3 kV (the lower voltages being used for Vertical Take-Off & Landing (VTOL) air taxis and the higher voltages being used in regional jet applications such as the E Fan X demonstrator). This increase in operating voltages, will bring new challenges. The focus of the project was the management of arcs that take place within a faulted electrical system. The management of high current arcs is common in conventional electrical power systems, however the relevance, behaviour and implication of high current / high energy arcs in aerospace power systems is relatively unknown. The use of higher voltages in aerospace applications, the change in component technology (such as using screened instead of unscreened cables), system configuration (grounded / ungrounded) and use of composite structures within the aircraft will all impact on arc tracking / arcing behaviour. As such the ARCTRACK project worked towards understanding the arcing phenomenon in aerospace electrical architecture, with findings of the project aiding in improving standards, testing and materials.

The project showed that arc current is likely to be determined by the system impedance in future high voltage aircraft. This means that the maximum current flowing during a fault will likely be at a much higher magnitude than seen in existing aircraft. This should improve the ability of protection systems to detect faults and isolate them before damage occurs. However, there is a risk that faults involving composite airframes could result in a smaller current that is more difficult to detect. The project also identified methods to test electrical equipment used in the next generation of aircraft through experimentation carried out within a high voltage laboratory that generated 5000A of current at a frequency of 1kHz. The work carried out will inform the development of commercial test methods going forward. Finally. work took place to identify opportunities to adjust the design of cables for use in future aerospace systems. A hierarchy of measures to protect the aircraft from damage during an electrical fault was explored.
Work Package 1:This WP was led by University of Manchester and focused on the development of experimental capability suitable for the evaluation of arc tracking hazards in future high voltage aerospace systems. Early findings of the work package summarised the arc tracking test techniques in aerospace environment presented in literature including the details of the nature of electric arcs. A test circuit was designed to test with fault currents of Ipeak ≤ 5 kA with a variable frequency of 500-2000 Hz. The testing work showed that faults in which the arc travels through a larger electrode gap impose a more severe impact on the system safety due to the high energy dissipation. As the arc energy increases, the safety boundaries specified by incident energy calculations need to be increased to implement adequate protection methods for adjacent components. Tests at atmospheric pressure showed that a higher arc power is produced when compared with tests carried out at 0.2 and 0.6 bar. However, it is not clear that the combination of higher power/pressure is necessarily the worst-case scenario in respect to the ability of the arc causing damage.

Work Package 2: This WP was led by University of Strathclyde and was focused on the development of reusable accredited models of an aerospace electrical power system, configured to capture the interactions between arc track events and power system technologies. Work done within this package has informed the dedicated arc models being developed in WP1 by providing anticipated fault durations and power system fault levels before becoming the platform for these arc models to be integrated into. Using extensive modelling and simulation, the team investigated the systems-level impact of the arc tracking faults within future aircraft higher voltage electric power systems and provided recommendations for the improved detection and safe management of these.

Work Package 3: This WP was led by TE and focused on the test of cable materials and cables to evaluate the level of damage that fault currents in the next generation of high voltage aerospace systems could cause. The work sought to characterise the cable samples that will be used for experimental test. Data about the cable construction wee provided to WP2 and small-scale tests of the materials being used in the next generation of cables provided information on parameters such as CTI, permittivity, breakdown voltage.

Work Package 4 (Dissemination and exploitation): As a result of the project, TE is pleased to announce that it has now scaling up a range of cables, both screened and unscreened that provided PDIV values >2kV at 40K ft. The project has also advanced the state of the art in respect of the understanding of arc currents in the next generation of aircraft electrical systems. An open online presentation was organised, titled “Introduction to ARCTRACK” and was attended by over 50 delegates from all over the world. A second workshop was held in March 2021, which was attended by over 15 participants. This workshop presented the results of the entire project (as the timing coincided with the end of delivery of the project timeline). Further dissemination has taken place via SAE and European standards bodies through membership of the committees and through publication at conferences / in journals.
The project has resulted in the development of a clear understanding of arc tracking hazards and the manner in which they can be mitigated. While it has been more challenging to suggest a methodology to scale up the test methods the information the project has provided to the Topic Manager and the wider beneficiaries show that it is possible to to manage the arc hazard in an controlled manner (whether this be via cabling design / system level protection measures). The development and test of prototype cable systems will also assist the Topic Manager and wider sections of industry to understand the key risks, constraints and opportunities that exist in future commercial products. The simulation toolbox developed during the project will allow the Topic Manager to understand the impact of system level architecture changes on the probability of arc tracking damage.

The availability of simulation and experimental techniques to explore arc tracking will be a key enabler for other projects that are exploring new and alternative high voltage architectures for future commercial aircraft. The initiation of changes to existing standards or creation of new standards will assist and federate the development of new hybrid electrical architectures for the wider industry sector.
Aim of ARCTRACK and consortium members
XRD results of cable samples
Electrical power system modelled in WP2
Test chamber used in arcing tests