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.
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.
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.
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