Compared to the traditional aircraft, electrification of power system in aircraft has potential to revolutionise the aviation industry. Typically, more‐electric aircraft (MEA), even all‐electric aircraft has been developed and delivered to decrease the greenhouse gas emission and increase the energy efficiency. The next generation of MEA will operate at high voltage to facilitate the transfer of significant levels of electrical power in an electrified aircraft. However, the higher voltage inevitably leads to an increased risk to the insulation of the electrical components and power system. This study aims to provide a critical overview of the insulation challenges from the perspective of electrified aircraft, typically MEA application. The development of MEA and the special working conditions are explained at the beginning. Then the insulation challenges of power modules, electric machines, aeronautical cables etc. are discussed in detail. Finally, the existing technical barriers and future prospects of insulation for electrified aircraft are summarised. It provides a reference for the future design and test in power system of next generation MEA and related electrified air transportations.

Bushings are essential components in a power transformer where incipient partial discharge (PD) activities and its detection and diagnosis cannot be ignorant. In this paper, an oil-impregnated paper (OIP) bushing is modeled to investigate that the oil gaps between the flange and condenser body in a typical OIP bushing provide a feasible path to trace the electromagnetic signal. As a non-destructive method, UHF (Ultra High Frequency) is proposed to detect 4 typical inside and outside PD defects of 110 kV bushings. To analyze the parameters of different defects, not only phase-resolved partial discharge (PRPD) is presented, but also 16 detailed time-domain and frequency-domain parameters of UHF signal are involved. Then feature extraction and selection are conducted through comparative principal component analysis (PCA) and extremely randomized trees (ET) algorithms. It is revealed that the selected features are representative and ET greatly reduces the amount of data whilst ensuring high accuracy. Fault diagnosis for bushing is finally achieved via support vector machine (SVM) with the selected features. The presented work of bushing PD detection based on UHF sensors provides a complete solution for the bushing diagnosis in potential field application and maintenance.

More-electric-aircrafts (MEAs) are heading towards larger power, higher voltage, and more optimum architectures, it is extremely important to understand partial discharge (PD) behaviors under the challenging aeronautical power systems. PD under the pressure of 1–101 kPa and frequency of 50–1000 Hz is studied to emulate the practical situation with the consideration of insulation defects from electric machine windings. The high frequency current transformer (HFCT) is specifically employed to pick up partial discharge signals. Experimental results indicate that PD inception voltage (PDIV) decreases almost linearly with air pressure. As to the discharge amplitude, it increases first and then decreases as air pressure dropping. The highest discharge repetition rate and the number of discharges appear at 30 kPa. High frequency doubles the number of discharges without affecting PD amplitude. Low air pressure causes the phase shift and phase width of the phase-resolved partial discharge (PRPD) to increase, and the trend also is accelerated by high frequency. This experimental approach is beneficial to provide prerequisite knowledge in characterizing PD and assessing its potential adverse impact on the aeronautical power system and consequently contribute to optimizing the insulation design for MEA.

Power electronic transformers (PETs) are becoming popular in the modern dc distribution grid due to their high efficiency and flexibility. To increase the power density of PETs, high-switching frequency would be adopted for the power switches. However, this may eventually increase the risk of partial discharge (PD) as the internal insulation space is reduced. In order to investigate PD characteristics in PETs under high-frequency pulse voltage, an experimental platform was set up in the laboratory, in which a twisted pair of wires model was used to test the insulation failure between windings in PETs. The PD behaviors were thoroughly investigated in the frequency range of 50 Hz to 20 kHz by time-resolved PD (TRPD). The results reveal that at high frequency, both the initial discharge voltage and discharge repetition would increase, while the PD amplitude decreases. Moreover, the PD pulses mainly occur at the field strength inversion of the rising and falling edges, the discharge time width tends to increase at high frequency. By analyzing the discharge model under pulse voltage, the discharge amplitude decrease and discharge times increase due to the difference of charge accumulation field intensity and effective discharge time at different frequencies. Under high-frequency voltage, the number of PD and the proportion of discharge time is much higher than 50 Hz, which may be the main reason for high-frequency insulation failure prematurely. According to the insulation life model based on the total discharge amplitude, the insulation life of 20 kHz is slightly higher than 10 kHz. When designing HFT, 20 kHz should be elected as operation frequency rather than 10 kHz.

As an essential component of power transformers, the detection and diagnosis of incipient partial discharge (PD) activities of bushings are of great significance. A 35‐kV oil‐impregnated paper (OIP) bushing is investigated. The bushing is modelled by coaxial theory and electromagnetic (EM) simulation. As the paths of PD‐induced ultra‐high frequency (UHF) signal propagating in the bushing are OIPs and oil gap, small attenuation during signal propagation is seen. Since OIP is composed of heterogeneous media compared with pure oil, there will be relatively less UHF signal leakage from OIPs, whereas more leakage from the oil gap. This leakage provides the possibility of non‐contact detection outside the bushing by UHF method. PD measurements with UHF method are carried out on the bushing. Then, the minimum energy method is used to extract time‐difference‐of‐arrival (TDOA), and Chan algorithm is adopted to locate points of UHF signal radiation. High accuracy locating with a small error of 15 cm has been achieved. The contactless UHF method‐based tests have demonstrated the effectiveness of online monitoring and locating of bushing PD.