This article investigates the evolution of electrical properties of polyethylene terephthalate (PET) with thermal aging. Electrical tests are performed within a wide range of frequencies in order to simulate the application conditions of insulating materials in inverter-fed machines. In particular, for the aging conditions considered, the real part of permittivity showed to be correlated with the concentration of the degradation species, investigated through FTIR. On the contrary, the dielectric breakdown at high frequencies showed to be independent from the corresponding values of the dissipation factor (tanδ). This behavior would imply that thermal runaway is not the principal phenomenon leading to the dielectric failure.

Traditional methods for characterizing piezoelectric materials typically involve analyzing their electromechanical response, focusing on coefficients such as the piezoelectric strain coefficient d33. In this study, an alternative approach is proposed to evaluate the piezoelectric response by examining the surface charge accumulated in the tested sample following a corona polarization process. Through the use of an electrostatic voltmeter, two influential factors affecting the piezoelectric response were investigated: the number of needles employed during the polarization and the presence of a grid interposed between the high-voltage needles and the specimen.

Short-width voltage waveforms, here as short as one microsecond, are good approximation of the turn-turn electrical stresses in machine fed by converters with very short rise times. This study shows that partial discharge inception voltage of turn-turn models under such circumstances is higher than the one for longer pulses, possibly challenging the idea that the extremely short rise times are always correspondent to worse inception conditions for the insulation.

This review-type article highlights the challenges ahead in aircraft electrification, with the goal of stimulating researchers from academia and industry to contribute to this complex, fascinating topic. This article demonstrates the role of dielectrics in reliability of transport electrification.

In an electrical drive, the impulsive waveforms of the power inverter can increase the electrical stress on the insulation system of the rotating machines to a point where partial discharges are incepted, and failure occurs in very short times. Electrical drives in aerospace applications are subjected to even more challenging operating conditions, due to the reduced pressures, which highly enhances the probability to incept Partial Discharges. A solution often proposed by manufacturers involves the use of the so-called Corona Resistant (CR) materials, which are proved to be able to withstand a limited amount of PD activity in industrial drives. However, their performance in conditions typical of aerospace applications has not been verified yet. Thus, this paper investigates the endurance of twisted pairs featuring different types of corona-resistant insulations placing them in a reduced pressure environment under voltage impulse repetition frequency typical of modern electrical systems based on silicon carbide MOSFETs. Considerations on the feasibility of CR insulation systems for applications such as the more electrical aircrafts are discussed, with apparently negative indications.

The feasibility of detecting PD in inverter-fed machines using acoustic emission sensor realized using fiber optics was investigated. The sensors, have a frequency response up to 500 kHz and are interrogated using a fiber-optic interferometric system. Three acoustic emission sensors were attached to the stack of the stator to explore the possibility of both PD detection and localization. Results were compared with those achieved using electrical detection and those provided by an ultrasonic camera. Preliminary tests using AC sinusoidal waveforms did show that the acoustic emission sensors and the ultrasonic camera could couple PD activity with the same sensitivity of a conventional electrical PD detection system having a sensitivity of 10 pC. Repetitive voltage impulses were found to cause a high disturbance level in both the acoustic emission sensor and the ultrasonic camera. The noise was ascribed to vibrations induced by the electrodynamic stress due to the impulsive charging current. However, working on the AE sensors in the frequency domain, it was possible to highlight frequency ranges where the PD signal exceeded the disturbance, thus enabling PD detection. The same was not possible for the ultrasonic camera.

Electrical converter-cable-machine systems, such as those in renewable source interfaces and transport drives, are operated with increasingly fast and high-performance converters. Their effects on the stator insulation and, in particular, on the turn insulation, need be understood in detail. A dynamic/FEM model is used to simulate the maximum voltages stressing the turn-to-turn and phase-to-ground insulation. The results show the role of rise time in the generation of overshoots and uneven voltage distribution. For machine to be fed with wide-bandgap converters, the limitations of PD testing using conventional surge generators are highlighted. Besides, the limits of the rise time definition and its role in the IEC60034-18-41/42 standards are discussed with reference to non-ideal waveforms acquired from a SiC bipolar converter.

Corona-resistant winding wires help to mitigate the impact of partial discharge activity in inverter-fed machines. Despite the fact they are on the market since about 20 years, it is still unclear how wires with different insulation systems should be compared. We propose a combined thermo-electrical procedure that might help to provide a more accurate ranking of the wires assuming that corona-resistant winding wires might help to prevent premature failure, but they will not be able to withstand partial discharge activity throughout the expected lifetime of the insulation (e.g. 20 years).