Grounding Topologies for Resilient, Integrated Composite Electrical Power Systems for Future Aircraft Applications

Abstract

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 Route to Sustainable Aviation: A Roadmap for the Realization of Aircraft Components With Electrical and Structural Multifunctionality

“…For low frequency current return over composite structures, metallic grounding rails are used to form a low resistance grounding network [16,17,61]. Attainment of a LoMF1, with minimal cable harnesses and [19,20,38,39]. A significant challenge to enabling a LoMF2 for a low frequency current return through CFRP is that a conventional CFRP plane has significant electrical resistance which makes equipotential bonding difficult to achieve [61].…”

“…To enable fault detection via differential unit protection, the resistance added to the fault path by the CFRP would need to be tuned to be below thresholds identified in [20] Areas to pursue for this are CFRP lay-up, panel size and approach to electrically bonding the CFRP to ground. An alternative approach may be to use a high resistance grounding (HRG) topology [19], which restricts the fault current, thereby decoupling fault response from the fault path resistance. The EPS does need to be rated for the step increase in network voltage relative to ground when a first rail to ground fault occurs.…”

“…[15]; and, (3) use of CFRP as a high frequency ground plane with metallic low frequency ground rails laid over CFRP [16][17][18]. Limited studies on the low frequency response of CFRP to electrical fault current, and resulting choices of grounding topology are discussed in [19], but the use of CFRP for the low frequency ground rails is not explored. As noted in [20], a major challenge for low frequency conduction of electrical current is the low electrical conductivity of CFRP.…”

Electrical protection solutions enabling integrated electrical power and composite structure systems for aircraft

“…In the event of a rail to ground fault in the integrated system, the CFRP structure may form part of the conductive pathway to ground for the electrical fault current, as indicated in Fig. 1, which shows the path taken by fault current, If (A), through CFRP to ground, where a fault has occurred due to vibration-induced chaffing of a power cable against a CFRP panel [6].…”

Impedance analysis of current return networks in composite aircraft based on partial element equivalent circuit

“…Introduction: Composite materials with lower conductivity, especially carbon fibre reinforced plastics (CFRP), cannot provide an ideal ground plane for aircraft like metal structures fuselage, which will greatly affect the electrical performance of the whole machine [1,2]. Therefore, the FAA proposed that the composite aircraft should be equipped with independent current return wiring for the electrical system in the aircraft grounding protection manual and advisory.…”