Partial discharge (PD) as one of well-known signatures of defects in the insulation system of high voltage equipment has been studied over eight decades. It is of a great interest to power grid operators and owners to identify and distinguish local weak spots in insulation system of the key components of power system by using the obtained PD information to make timely decision thus to avoid any unexpected failures in the system. This article reviews the research progress of PD in high voltage apparatus, including motors and generators, cables, transformers and gas insulated equipment, with attempts to assess the severity of different types of PD initiating defects as well as key PD features that can be selected for classifying defects. Experimental and on-site test results for each type of discharge and defect associated are summarized and discussed. Also, development of these defects during operation of equipment caused by changes in physical and chemical parameters of defect and/or insulation, and its impact on phase-resolved PD pattern variation are thoroughly explained. It is expected that this paper can provide a comprehensive guideline for PD data analysis of available PD information extracted by conventional PD acquisition instruments for both engineers and asset managers of high voltage apparatus.

The reliability of the insulation of commercially used high-voltage insulated gate bipolar transistor (IGBT) subjected to untimely initiation of partial discharge (PD) at low pressures and high temperatures is investigated and discussed in this letter. To date, no research has addressed the vulnerability of the high-voltage IGBTs to the PDs at harsh environmental conditions for aerospace applications. This letter aims to fill this gap and illustrate the PD characteristics initiated between the electronic components inside the silicone gel. To this end, five commercial 3.3-kV IGBT modules and four 4.5-kV IGBT modules were tested at ac voltage under low pressures (20, 15, and 10 kPa) and high temperatures up to 120 °C. An efficient PD test method and an anti-series connection configuration are suggested, which emulate a realistic operational scenario for IGBTs together with the one suggested by the current standard. Experimental results reveal the occurrence of inconsistent PDs initiating from possible dynamic PD source inside the gel at low pressures, and more intense and consistent PDs when the temperature increases. It is expected the findings highlight the importance of PD tests on IGBTs at the abovementioned operation conditions and provide a selection and modification guidelines of PD-free IGBTs for manufacturers and engineers in the aerospace industry.

It is an urgent requirement to suppress surface partial discharge (PD) activities of dielectrics for modern electrical and electronic devices. Here, we introduce a method to mitigate the surface PD in a manner of tailoring insulation surface conductivity. A surface coating with a conductivity ranging from 10⁻¹³ to 10⁻¹⁰ S is developed to regulate the surface charge migration in the vicinity of the triple junction and to suppress effectively the surface PD activity. The excellent performance of this coating provides an approach for surface PD suppression at DC voltage, which has great application potential in the insulation design of DC electric power equipment, DC generators, power electronic devices, printed circuit board (PCB) layout, and various integrated electrostatic sensors and actuators.

The safe and reliable operation of insulation material used in key high voltage components under extreme environmental conditions represents the major concerns for manufacturers and operators of More Electric Aircrafts (MEA). Surface discharge occurring in high current carrying components in DC power system diminishes the insulation material’s performance and life, especially at high‐temperature conditions. Here, the surface discharge behaviour of two commonly used high‐temperature insulation materials, ethylene‐tetrafluoroethylene (ETFE) and polyetheretherketone (PEEK) is studied at different temperatures under ramp and DC voltages. Extracted partial discharge (PD) features are presented and the impact of voltage polarity on surface discharge propagation is discussed. Our studies reveal that, while both materials exhibit non‐linear PD behaviour with respect to their electrical conductivity, ETFE generally shows PDs with higher intensity at high temperature above 100°C with a higher possibility of surface discharge due to its lower permittivity. Overall, the PD mechanism in high‐temperature, DC voltage applications is explored, and a basis for the selection of high‐temperature PD suppressing materials is developed.

Aircraft electrification poses new challenges to the safe design of the insulation system under harsh operating conditions. This study focuses on the investigation of electrical treeing, a precursor to electrical breakdown in the bulk of electric wire and cables, under emulated low pressure and high temperature for high density electrification at high altitude. It was found in a model insulation of cross-linked polyethylene (XLPE) that low pressure and high temperature significantly decreased the treeing initiation voltage and increased tree growth propagation rate. Moreover, the presence and size of artificial air gap affected tree morphology, growth rate, and fractal dimension in a way that decreases insulation durability. The effect of pressure on treeing growth was studied by using the partial discharge (PD) measurements, which suggested lower pressure increased PD activities, with respect to the rate and magnitude of PDs during both stages of treeing initiation and propagation. This work could be used as a baseline for studying electrical treeing phenomenon at high altitudes with coupled high temperature-low pressure, to pave the way for the reliable design of insulation systems on the path towards aircraft electrification.

A model DC material based on ethylene propylene rubber (EPR) including the pure EPR and the EPR-based nanodielectrics incorporated with two different nanoclays, Kaoline and Talc, under operational conditions was investigated. The operational conditions include a 20 kV/mm electric field at 25 °C, a 20 kV/mm electric field at 50 °C with a thermal gradient, and a 40 kV/mm electric field at 50 °C with a thermal gradient and polarity reversal. Space charge distribution, surface potential, and electrical conductivity were measured to characterize the model DC material and interpret the discrete charge dynamics in the bulk and at the interface of the three samples. The experimental results revealed that the electrical conductivity of Talc-filled nanodielectric has the least dependency on electric field and temperature, which reduces the conductivity gradient across the dielectric. Moreover, the successful suppression of space charge and the lower dielectric time constant in the Talc-filled nanodielectric result in a tuning electric field in the bulk not only under normal operating conditions but also more importantly under polarity reversal conditions. The maximum of absolute charge density decreases from 10.6 C/m³ for EPR to 2.9 C/m³ for the Talc-filled nanodielectric under 40 kV/mm with polarity reversal and at 50 °C with the thermal gradient. The maximum of local electric field enhancement for the mentioned condition reduces significantly from 97 kV/mm, 142% enhancement, for EPR to 45 kV/mm, only 12.5% enhancement, for the Talc-filled nanodielectric.