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The escalating adoption of wide-bandgap (WBG) semiconductor devices in power electronics has led to the generation of high-frequency, high-slew-rate voltage waveforms, which exert significant stress on encapsulating materials such as silicone gel (SG). This study systematically investigates the breakdown performance of SG under DC,60 HzAC, and highfrequency square wave excitations. Breakdown voltage assessments were performed across a frequency range of 10 to 50 kHz for square pulses with 100 ns rise time, revealing a pronounced decline in dielectric strength as frequency increased. Specifically, the breakdown voltage measured under DC conditions, which was 20.6 kV, diminished by 84.9 % when subjected to a square wave excitation at 50 kHz. Furthermore, electric field simulations elucidated the phenomenon of localized field intensification occurring near the needle tip, which corresponded with the identified breakdown locations. The key revelations from this research underscore the limitations inherent in conventional testing methodologies, which fail to adequately characterize the degradation behavior of SG under realistic high-frequency fast-rise square voltage stress conditions. 

Wide bandgap (WBG) and ultra-wide bandgap (UWBG)-based inverters are increasingly being adopted in More Electric Aircraft (MEA) and All Electric Aircraft (AEA) due to their ability to operate at higher switching frequencies with improved efficiency and power density. However, these advantages come with drawbacks, including increased electrical stress and exacerbation of AC losses, such as the skin effect and proximity effect. Litz wire, known for its effectiveness in mitigating these losses, is becoming a preferred conductor in highvoltage, high-frequency aerospace applications. This study investigates the breakdown voltage behavior of Litz wire insulation under square wave voltage stress across different frequencies. Twisted-pair Litz wire specimens were tested using a state-of-the-art high-voltage pulse generator with fixed rise times to emulate inverter-fed conditions. The resulting breakdown voltages were statistically analyzed using the Weibull distribution to evaluate insulation strength and failure predictability. The findings offer new insights into the insulation characteristics of Litz wire under realistic high-frequency converter stress and support the development of converter-resistant insulation systems for next-generation aerospace electrical power systems (EPS). 

Partial discharge issues at the triple junctions of the copper-ceramic-silicone gel interfaces in power electronic modules have emerged as a critical barrier to further technological advancement. Therefore, accurately calculating the electric field intensity and optimizing the insulation system are essential to ensure module reliability and performance. In this study, 2D and 3D geometries of a commercial power module were modeled in COMSOL Multiphysics to analyze the electric field distribution around triple points. The results showed a maximum electric field intensity of 22.5 kV/mm in the 3D model, compared to 15.0 kV/mm in the 2D simulation. This finding emphasizes the critical importance of employing 3D modeling to accurately represent the intricate electric field distribution at triple-edge regions. This work lays the foundation for accurate electric field calculations within power electronic modules, which is essential for determining the extent of electric field mitigation required. 

Most research involving resistive field grading materials or nonlinear field-dependent conductivity (FDC) layers has predominantly concentrated on DC or sinusoidal AC voltages, even though (U)WBG power electronic modules typically operate under high-frequency square wave voltages. To bridge this existing research gap, the present study systematically investigates the efficacy of an FDC coating in alleviating electric field stress when subjected to high-frequency, high-slew-rate square wave voltages. The findings indicate that applying a nonlinear FDC layer significantly reduces electric field stress, even under stringent conditions involving elevated operating frequencies. Furthermore, the influence of the square wave voltage type—the distinction between unipolar and bipolar square waveforms—on electric field stress remains inadequately understood despite substantial progress in breakdown and PD experiments related to these phenomena. Consequently, this study undertakes a comparative analysis of nonlinear FDC layers' performance under unipolar (+27.5 kV) and bipolar (±27.5 kV) square wave voltages. In doing so, this investigation contributes valuable insights into the interplay between high-frequency operation, the polarity of square waveforms, and the efficacy of nonlinear FDC layers in mitigating electric field stress within (U)WBG power module packages. 

Insulation in electric machines is vital in determining system reliability and lifespan, especially under extreme environmental conditions. With the rapid shift toward More Electric Aircraft (MEA), All Electric Aircraft (AEA), and advanced space missions, electric motor components must perform reliably under low pressures, wide temperature ranges, and exposure to radiation. Magnet wires are central to motor operation, and their insulation must withstand high voltage stress in these demanding conditions. While prior research has predominantly focused on insulation performance under AC or pulse width modulated (PWM) waveforms and partial discharge (PD) behavior, there is a limited understanding of dielectric strength under direct current (DC) stress, particularly at reduced atmospheric pressures. This paper presents an experimental investigation into the DC dielectric strength of three magnet wire types (15 AWG, 18 AWG, and 20 AWG) tested at three pressure levels: 101kPa,80kPa, and 40 kPa. Using a voltage to breakdown with a constant ramp method, the study evaluates the insulation's withstand capacity across wire sizes and environmental pressures. 

Incorporating nonlinear resistive field grading materials (FGMs) onto metal-brazed substrates has been widely investigated as an efficient electric field reduction strategy at triple points (TPs) within ultrawide bandgap [(U)WBG] power modules. However, most investigations have been carried out using either dc or sinusoidal ac voltages despite actual (U)WBG power modules operating with high-frequency square voltages featuring high-slew rate ( dv/dt ). Thus, this study introduces a field-dependent conductivity (FDC) layer to analyze electric field reduction under high-frequency, high-slew-rate square voltages. Using COMSOL Multiphysics, both coated and uncoated structures were modeled to evaluate electric field reduction. When employing nonlinear FDC coating, the findings demonstrate a notable decrease in field stress, even under square voltages with rapid rise times and high frequencies. However, relying solely on the nonlinear FDC layer may not adequately address the electric field concerns, particularly when factoring in protrusions on metallization layers and reducing layer coverage. In response to this challenge, protrusions at the metal ends are incorporated into a protruding substrate configuration. This entire structure is then coated with a nonlinear FDC layer. The combined impact of the protruding substrate and nonlinear FDC layer effectively reduces the electric field. However, when the rise time is shortened to 75 ns and the frequency is raised to 500 kHz, the electric field stress around TPs exceeds the insulation’s withstand strength. This finding underscores the need for further research into alternative strategies as the prevalent strategies are unable to effectively mitigate electric fields in real-world operating conditions of (U)WBG power modules. 

Electrical insulation is the limiting factor that reduces the lifetime of power components. The aging of insulation, which is heavily caused by partial discharges (PDs) and harsh environmental conditions, eventually leads to complete insulation breakdown. The advancement in developing more- and all-electric aircraft is limited by the existing apparatuses that operate at lower voltages. High applied voltage and lower ambient pressure, commonly envisaged in more and all-electric aircraft, pose significant challenges, as their effects on PD activity and space charge accumulation differ, thereby affecting the apparatus's lifetime. To improve the reliability of aircraft electric motors' performance, it is essential to accurately predict the breakdown performance of the magnet wires used as windings in the motors at low-pressure levels. In this article, we investigate the effect of low pressures on the breakdown voltage of magnet wires with insulation Type I. 

Statistics indicate that more than 85% of equipment failures are related to insulation failure. Such faults can lead to brownouts and blackouts and in the transportation electrification context can also impact the safety of personnel or jeopardize missions, which is highly unacceptable. In this regard, predicting a fault before it occurs to do planned maintenance is needed where partial discharge (PD) activity can be used as an indicator. The paper presents a model based on the time of arrival (ToA) approach for PD localization in medium voltage (MV) cables which are a critical component in powertrains and distribution grid connections. The cable considered, which is a three-phase MV cable with three single-core armored copper conductors is modeled using a frequency-dependent wideband model in EMTP. The model accurately represents the cable's behavior by incorporating the skin effect and the impact of semiconducting layers on signal propagation. The attenuation coefficient is calculated for varying frequencies and lengths to evaluate the effect of the semiconducting metallic screen and attenuation voltages. An empirical relationship is developed by injecting PD signals at predefined locations and analyzing arrival time differences at cable terminals, linking propagation velocity, cable length, and ToA. The proposed methodology ensures precise PD localization, highlighting its potential for enhancing diagnostic accuracy in cable systems. 

Air has always been an insulation medium that mainly interfaces with solid dielectrics within power electronics building blocks (PEBBs). Equipped with wide-bandgap (WBG) and ultrawide-bandgap (UWBG) devices, air around sharp edges is stressed by high frequency, high slew rate square wave voltage pulses within PEBBs. Having a lower insulation strength than solid dielectrics, decreased dielectric strength of air due to high frequencies and high slew rates of applied voltage can lead to enhanced surface discharges at interfaces, leading to degradation of solid dielectrics and eventually their breakdown. This shows the importance of studying the rise time and frequency effect on air breakdown subjected to the square wave voltage pulses at normal pressure, which is the main objective of our research. This study focuses on understanding the air breakdown voltage behavior under a frequency range of 2.5 kHz to 75 kHz and a rise time between 50 ns and 150 ns. This study reveals that a higher breakdown voltage (BDV) occurs at longer rise times, consistent with previous research, except for 150 ns, in which the expected effect was not observed. Results showed that BDV decreases with frequency increases beyond 20 kHz. For 75 kHz and a rise time of 125 ns, BDV reduces by 30 % to that of 10 kHz.