The aviation sector is one of the main contributors to greenhouse gas emissions and there is a need to develop more-electric aircraft (MEA) that are operationally efficient. In traditional aircraft, the limited number of electrical systems operate at low voltage. The next generation of MEA will operate at voltages of above 1 kV to facilitate the transfer of significant levels of electrical power in an aircraft. However, the higher voltage and frequency levels will lead to an increased chance of partial discharge (PD) degradation in the insulation systems. Therefore, it is critical to have an accurate method of PD detection available for use in these new aircraft. Conventional PD detection methods are optimized for 50/60 Hz applications in the power industry and can be disturbed by harmonics generated via power electronic devices operating at high frequency. This paper explores a bespoke PD detection technique developed using a Sagnac optical fiber sensor capable of measuring the frequency-dependent PD information. Tests were conducted in the 50–1000 Hz range in which existing variable frequency AC power systems are being used in MEA. The results demonstrate that the increasing frequency will have an adverse effect on PD and must be considered in MEA design.

Power cables connecting floating offshore wind farms will see mechanical stresses not experienced in land-based networks. Cross-linked polyethylene (XLPE) samples from power cable were subjected to compressive and tensile strains of up to 5% to examine how electrical tree growth is affected. A total of 35 samples were tested using needle-to-plane geometry and 50-Hz ac voltage at 7.5 kVrms. Compressive strain widened electrical trees along the direction strain was applied, and tensile strain led to narrower trees, distorting their rotational symmetry, and confirming a mechanical influence on growth. The distortion was linear with strain magnitude. The likelihood of increased tree branch bending or bifurcation angles linearly increased with compressive strain and reduced linearly with tensile strain. The fractal dimension of the trees was unaffected. Strain did not significantly influence the growth rate of trees until a value of 5% was reached. At this value, compressive strain reduced growth rate by a factor of approximately 2, whereas tensile strain showed no influence. Increasing compressive strain was also shown to linearly delay tree initiation. The influence of tensile strain was not quantifiable as trees initiated readily. The evolution of phase-resolved partial discharge patterns (PRPD) was unaffected by the strain applied. Time-to-failure was decreased by a factor of 1.8 at 5.7% tensile strain, which could have significance to in-service usage of high-voltage cables under dynamic forces found in floating applications.

Arcing in future high-voltage aerospace systems could occur more frequently and cause irreversible damage to electrical components, system structure and increase the risk of fire. While arcs seen in low-voltage aerospace systems tend to be long-duration and low-energy events, higher power but short-duration arcs may occur in high-voltage aerospace systems if they are readily detectable by system protection. This paper investigates the characteristics of high current arc faults generated at the AC frequencies expected in future rotating machines used for higher voltage aerospace systems. As such, arcs with a peak current up to 4.6 kA are generated at frequencies in the range of 0.5-2 kHz using an underdamped RLC circuit, under pressures of 0.2-1 bar absolute. High frequency arcs exhibit a similar characteristic to lower frequency arcs. A reduction in pressure results in lower arc voltage and arc power. Arcing tests at atmospheric pressure may therefore represent a worst-case scenario and the development of a low-pressure test environment may not be necessary. A black box model is developed to provide good agreement with experimental arc voltage waveforms for different parameters investigated in this study. This is a generalized modeling approach to estimate high-frequency high-voltage arcing characteristics without recourse to experiment.

SF₆ is widely used in modern transmission and distribution networks because of its outstanding dual qualities: arc quenching and dielectric insulation. As a gas medium, SF₆ is chemically inert, non-toxic, and non-flammable, which makes possible the construction of compact SF₆ switchgear. One major known disadvantage of the gas is that it has a global warming potential which is 23,900 times higher than CO₂. This has led to research into alternative gases with a much lower environmental impact, and one of the emerging candidates is CF₃I. The high boiling temperature of CF₃I means that it has to be used as part of a mixture inside gas-insulated equipment. To carry out the investigation on CF₃I, a scaled-down coaxial system that replicates the maximum electric field of a 400 kV GIL system was designed and fabricated. The insulation performances of CF3I/CO₂ and CF₃I/N₂ gas mixtures were then examined by measuring the 50% breakdown voltage, U₅₀, using a standard lightning impulse waveform (1.2/50) under absolute pressures of 1 to 4 bar. The experimental results show that CF₃I gas mixtures have promising potential as an insulation medium for application in gasinsulated lines.

There is increasing interest in developing aircraft that are wholly electric or utilize hybrid-electric architectures to deliver a reduced carbon footprint. The higher operating voltage is necessary to deliver electrical machines with an acceptable power density, which will increase the risk of partial discharge (PD), especially in the low-pressure environment at high altitude. This paper reviews the opportunity to use high dielectric strength gases to improve the PD performance of electrical machines for aerospace applications. PD characteristics of machine winding wires are tested in air, CO ₂ , SF ₆ , CF ₃ I, C ₃ H ₂ F ₄ , and C ₃ F ₇ CN. Mixture ratios of 60% C ₃ H ₂ F ₄ / 40% CO ₂ and 30% C ₃ F ₇ CN / 70% CO ₂ can remain gaseous under atmospheric pressure at a temperature of -30 °C, with the partial discharge inception voltage (PDIV) of machine winding wires approximately three times higher in these mixtures than air at 0.2 bar absolute. The test results have been applied to demonstrate that a machine using a high dielectric strength gas as part of its insulation system could tolerate a higher DC bus voltage while still being considered as Type I (PD-free). Additionally, endurance tests using insulating gases demonstrate the prospect of an improved time to failure for Type II insulation systems.