The upwards trend for the use of electrical power on state of the art aircraft is resulting in significant change to the design of power system architectures and protection systems for these platforms. There is a pull from the aerospace industry to integrate the electrical power system with the aircraft's structural materials to form an embedded system, reducing the need for bulky cable harnesses. This directly impacts the fault response for ground faults and ultimately the development of appropriate protection systems. Such structural materials include composites such as carbon fibre reinforced polymer (CFRP). This paper presents the experimental capture and analysis of the response of CFRP to electrical fault current, which indicates the need for two distinct sets of electrical ground fault detection criteria for low and high resistance faults and identifies the threshold resistance for this distinction. By extrapolating these results to develop models of CFRP for use in transient simulation studies, the key electrical fault detection thresholds for speed, selectivity and sensitivity for a DC system rail to ground fault through CFRP are identified. This provides the first set of key factors for electrical fault detection through CFRP, providing a platform for the design of fully integrated structural and electrical power systems, with appropriate electrical protection systems.Index Terms-Carbon fibre reinforced polymer, electrical protection, more-electric aircraft.Electrical and thermal effects of fault currents in aircraft electrical power systems with composite aero-structures.S
The upwards trend for the use of electrical power on state of the art more-electric aircraft (MEA) has resulted in a significant changes to the electrical power system (EPS) for these platforms due to increased use of DC, higher voltage and power levels, and decentralized architectures. A dual trend is the increasing use of carbon fibre reinforced polymer (CFRP) for aircraft structures, due to the superior mechanical properties of CFRP compared to metallic structures. However, the poorer electrical conductivity of CFRP results in the aircraft structure no longer being fully integrated with the electrical power system. There is a need to integrate these two systems to fully maximize the performance benefits of CFRP, and optimize the weight and volume of the electrical power system. A first step in this integration is to identify an appropriate fault management strategy, which enables the detection of higher resistance ground faults through CFRP. This includes the consideration of appropriate grounding topologies. This paper proposes the implementation of a high resistance grounding topology, which enables the detection and location of a fault via spectral analysis of the voltage across the grounding resistor. From this, implications for wider EPS and CFRP designs to enable the reduction in the use of bulky cable harnesses, providing the first step to CFRP becoming an integral part of the EPS, are discussed.
A tool for component sizing for MMCs has been developed and tested through simulations in PLECS. The steady-state behaviour under grid frequency deviations -interesting for offshore wind farm connections -has been analysed, providing insights in MMC characteristics and further testing the proposed tool.
Dc distribution minimises the number of power conversion stages and hence it lowers the overall cost, power losses and weight of a power system. Critical systems use IT grounding because it is tolerant to the first-fault. Hence, this is an attractive option for hybrid electric aircraft (HEA), which combines gas engines with electric motors driven by power electronic converters. This letter proposes an accurate implementation for the procedure of first-fault detection with IT grounding. Ac component injection along with the Sliding Discrete Fourier Transform (SDFT) is used to estimate the fault impedance. The procedure is very accurate due to the heavy filtering of the implicit moving average filter (MAF). Further computation savings are obtained by using the double look-up tables and the Goertzel algorithm for the SDFT. Results are validated by simulations and experiments.
Electrical propulsion has been identified as a key enabler of greener, quieter, more efficient aircraft. However, electrical propulsion aircraft (EPA) will need to demonstrate a level of safety and fault management at least equal to current aircraft. This will rely heavily on the capability and design of the electrical fault management (FM) system. Given the functional limitations and current lack of availability of FM technologies suitable for a future EPA application, strategic development of FM devices is required. Whilst there are a variety of roadmaps for EPA concepts and some of the key electrical components, the necessary strategic development of FM solutions targeted towards EPA has yet to be established. This paper proposes FM strategy maps which go beyond projections of expected development in various FM technologies to scope the feasibility of key FM solutions. This method can then be used to present FM technology projections, electrical oversizing and wider system redundancy alongside the various aircraft concepts in development. This results in strategy maps which capture the impact of any FM technology barrier on the viability of a given aircraft concept, enabling critical FM solutions to be integrated into the wider electrical system development. Index TermsFault management strategy map, electrical propulsion aircraft, electrical power systems, protection technology development. I. INTRODUCTIONElectrical propulsion has been identified as a key enabler of greener, quieter, more efficient aircraft. Novel electrical propulsion aircraft (EPA) will depend on the development of a range of electrical technologies, many of which are currently at low TRL (Technology Readiness Level). Given the risk that an EPA concept may rely on key technologies which may not be sufficiently developed as desired at the aircraft's point of entry into service, it is important to develop understanding of the particular challenges which must be addressed in bringing technologies to maturity. One of the most challenging set of technologies for EPA are the fault management (FM) devices,
Bidirectional power converters are considered to be key elements in interfacing the low voltage dc microgrid with an ac grid. However to date there has been no clear procedure to determine the maximum permissible fault isolation periods of the power converter components against the dc faults. To tackle this problem, this paper presents an electro-thermal analysis of the main elements of a converter: ac inductors, dc capacitors and semiconductors. In doing this, the paper provides a methodology for quantifying fault protection requirements for power converter components in future dc microgrids. The analysis is performed through simulations during normal and fault conditions of a low voltage dc microgrid. The paper develops dynamic electrothermal models of components based on the design and detailed specification from manufacturer datasheets. The simulations show the impact of different protection system operating speeds on the required converter rating for the studied conditions. This is then translated into actual cost of converter equipment. In this manner, the results can be used to determine the required fault protection operating requirements, coordinated with cost penalties for uprating the converter components. Index Terms--Microgrid, DC fault current, AC-DC power conversion, thermal design, power semiconductor diode switches, thermal stress, fault protection requirements. Graeme M. Burt (M'95) received the B.Eng. degree in electrical and electronic engineering from the University of Strathclyde, Glasgow, UK, in 1988, and the Ph.D. degree from the University of Strathclyde in 1992, following research into fault diagnostic techniques for power networks. He is currently a Director of the Institute for Energy and Environment at the University of Strathclyde, where he also directs the University Technology Centre in Electrical Power Systems sponsored by Rolls-Royce. He is a professor of electrical power engineering, and has research interests in the areas of: integration of distributed generation; power system modelling, real-time simulation, protection and control; microgrids and more-electric systems.
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