Partial Discharge Inception Voltage Research Articles

Analysis of properties and statistical study on partial discharge inception voltage using normal and Weibull distributions for vegetable oil-based nanofluids

Analysis of properties and statistical study on partial discharge inception voltage using normal and Weibull distributions for vegetable oil-based nanofluids

Preventing partial discharge in liquid metal polymer composites under steep voltage pulses

Liquid metal polymer composites (LMPCs) offer viable solutions for deformable electronics, including sensors and actuators. To ensure the longevity of the deformable technologies, partial discharge (PD) must be mitigated as it causes premature material aging and device failure. While studies on the dielectric properties of LMPCs have mainly focused on AC voltage, a large number of deformable applications will inevitably involve power electronics for higher efficiency and power density. Consequently, addressing PD in LMPCs under repetitive steep voltage pulses generated by power electronic switches becomes important. This study employs an electric field cancellation technique using electrets to reduce the PD magnitude and increase the partial discharge inception voltage (PDIV) of LMPCs under steep square voltage waves. We placed either a non-electret or electret thin film on top of LMPC samples and conducted PD experiments in flat and bent test coupon arrangements. The results show that electrets can reduce PD magnitude and increase PDIV in both test arrangements. Furthermore, the study provides deeper insights into the experimental results by conducting the electric field analysis of the LMPC experiments through numerical models.

In-Depth Partial Discharge Inception Voltage analysis in Laminated Busbar by Means of Experimentations and Simulations

In-Depth Partial Discharge Inception Voltage analysis in Laminated Busbar by Means of Experimentations and Simulations

Partial Discharge Inception Modelling of Insulating Materials and Systems: Contribution of Electrodes to Electric Field Profile Calculation

Partial discharge inception modeling is a powerful tool for material investigation and insulation system design in order to achieve the objective of PD-free operation of insulation systems. Model validation, however, requires accurate and repeatable testing conditions, and the aim of this paper is to look at the influence of electrodes and electric field simulation on partial discharge inception model prediction accuracy. Awareness of the geometric electrode configuration is important to forecast both the typology of discharge and the corresponding partial discharge inception voltage value. It is shown, in fact, that inaccurate evaluation of electrode shape (e.g., its flat part and contour) might impact significantly on electric field estimation, the typology of incepted discharges, and, thus, on model accuracy, i.e., on partial discharge inception voltage prediction, which is the basis for the partial discharge-free design of insulating materials and systems. In particular, small electrode curvature radius variations do not significantly affect the PDIV value or PD typology identification. However, worsening electrode/insulation specimen contact can significantly impact PD inception and typology evaluation.

Role of Temperature in Partial Discharge Inception Voltage at Triple Junctions

Role of Temperature in Partial Discharge Inception Voltage at Triple Junctions

Towards a Holistic Approach to Inverter-Fed Machine Design: FEM-Based PDIV Prediction of Complete Windings

The Schumann inception criterion was used to predict the partial discharge inception voltage of insulation models representing both wire wound and form wound (hairpin) low voltage machines. It was found that the fitting parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> (the logarithm of the critical number of electrons that define the transition from Townsend to streamer discharge) is almost independent of material parameters when dealing with a given type of insulation (e.g., turn-to-turn using round conductors or flat conductors). These numbers can be fed to software for finite element analysis to provide a worst-case estimate of the partial discharge inception voltage.

On the influence of humidity on the breakdown strength of air—with a case study on the PDIV of contacting enameled wire pairs

The partial discharge inception voltage (PDIV) in contacting enameled wire pairs exhibits a marked decrease with increased air humidity. While existing literature mentions several potential mechanisms for this reduction, a comprehensive quantitative assessment of the associated effects is lacking. This research paper addresses this knowledge gap by providing a quantitative estimation of the combined impact of water on the gas’s ionization yield (effective ionization coefficient) and the modification of the gap electric field caused by water absorption into the bulk of the insulating coating and the associated microscopic and macroscopic polarization processes (dielectric permittivity). However, a comparison of the theoretical predictions with experimental data reveals that these factors alone cannot fully account for the observed reduction in PDIV. Therefore, the study explores additional mechanisms mentioned in the literature, with particular focus on the development of a semi-conductive layer on the insulation coating in humid atmospheres. The numerical simulations of the surface charge dynamics within this layer suggests that the frequency-dependent decrease in PDIV under high-humidity atmospheres can indeed be attributed to the modification of the gap electric field due to the accumulation of surface charge in the semi-conductive layer.

Photon counting technique as a potential tool in micro‐defect detection of epoxy insulation pull rod in gas‐insulated switchgears

AbstractThe micro‐defects in epoxy‐based insulation materials generate a local high electric field which results in continuous degradation, seriously endangering the insulation system of gas‐insulated switchgears. A highly sensitive detection technique is reported for micro‐defects of insulation pull rods based on the photon counting (PC) technique. The results demonstrated that for an epoxy‐based insulation pull rod, the photons released during electroluminescence and ionisation at 2 kV, which is less than the partial discharge inception voltage, can be clearly detected. The findings presented a strong correlation between photon counts and defect severity. Discourse has been conducted to elucidate the mechanism behind defect‐induced PC, employing the amplification of ionising luminescence through electric field distortion induced by micro defects and the augmentation of electroluminescence through the aggregation of trap charge. In this regard, the authors verified that PC can serve as a potential tool in the detection of micro‐insulation defects, which also has huge potential in online insulation condition monitoring.

A Novel Approach to Partial Discharge Detection Under Repetitive Unipolar Impulsive Voltage

Partial discharge (PD) detection is an important method to verify the reliability of the insulation structure of high voltage power electronics devices. Although there are many researches on PD detection inside power modules, they mainly focus on traditional electrical detection methods and 50 Hz working conditions, which do not meet the repetitive unipolar impulsive voltage conditions of power modules, and traditional methods cannot solve the electromagnetic interference (EMI) problem under working conditions. This paper proposes a novel approach to PD detection in power modules. This approach designs an optic fiber sensing (OFS) system based on optic theory, and conducts the detailed mathematical theoretical deduction. In addition, A partial discharge inception voltage (PDIV) signal processing method based on PD acoustic signal is proposed. Finally, the proposed approach is applied to a power module. The PD signal and PDIV is successfully captured without EMI interference and new insulation problems.

Investigation and Evaluation of High-Temperature Encapsulation Materials for Power Module Applications

With the advent of ultra-wide bandgap (UWBG) semiconductor materials, such as Gallium Oxide (Ga2O3) and Aluminum Nitride (AlN), higher temperature and higher voltage operation of power devices is becoming realizable. However, conventional polymeric and organic encapsulant materials are typically limited to operating temperatures of 200 °C and below. In this work, six materials were identified and evaluated as candidates for use as encapsulants for operation and high-voltage insulation at and above 250 °C. High-temperature silicone gel was used as a reference material and was compared to five novel encapsulants including an epoxy resin, a hydro-set cement, two low melting point glass compounds, and a ceramic potting compound. Gas pycnometry was utilized to evaluate the voiding concentration to avoid partial discharge. Each material was then processed onto a direct-bonded-aluminum (DBA) substrate test coupon to evaluate compatibility with a commonly used metal-ceramic substrate and processability for use in a power module. The insulation capability of each material was evaluated by testing the partial discharge inception voltage (PDIV) across a 1mm gap etched in the substrate. The dielectric stability was then tested by soaking the materials in air at 250 °C for various intervals and observing the degradation of their PDIVs and appearances. The results of each test were compared, and conclusions were drawn about each material’s feasibility for use as a dielectric encapsulation material for a power module operating at temperatures exceeding 200 °C.

Use of Plat-Bar Electrode Media to Detect Partial Discharge in Epoxy Resin Materials on PCB Surfaces

The electric power system must have a protection system with reliable electric power isolation, so that the supply of electrical energy works properly and optimally. There are several kinds of disturbances in the electric power distribution system, one of which is a partial discharge. This study aims to investigate the effect of plate-rod electrodes on partial discharge, partial discharge voltage limits in solid insulation, and the characteristics of partial discharge in electrode media, and waveforms in partial discharge detection sensors. After conducting research, it was found that in the plate-rod type electrode media, the PDIV voltage appeared earlier than the plate-plate electrode media due to the cross-sectional area of the electrode media. And the limit of the pre-discharge voltage of PCB type solid insulation on the plate-bar electrodes is at a voltage of 1.3 kV. Several indicators to determine the characteristics of the partial discharge are background noise off (BGN off), background noise on (BGN on), partial discharge inception voltage (PDIV), and partial discharge voltage. After being examined, the value of each partial discharge detection voltage was obtained at negative and positive polarity voltages on the electrode plates and plate needles respectively 2.85 kV, 2.95 kV and 1.32 kV, 1.57 kV.

Deep Learning and Long-Duration PRPD Analysis to Uncover Weak Partial Discharge Signals for Defect Identification

This study focuses on improving the defect recognition accuracy under weak partial discharges (PDs) in epoxy resin through phase-resolved partial discharge (PRPD) analysis. The method is to refine the data rather than enhance the algorithm. Two measurement conditions are compared until PRPD pattern saturation is achieved: one-minute and one-hour durations. The PD data specifically target three void types located at different positions within the epoxy material. The aim is to evaluate how the presence of weak PDs at the PD extinction voltage (PDEV) influences defect recognition accuracy. This research sheds light on the potential implications of neglecting the significance of weak PD signals in defect detection. A convolutional neural network (CNN) model is trained using PRPD data recorded at the repetitive PD inception voltage (RPDIV) and tested using the new PRPD data from both conditions recorded from a lower PDIV to a PDEV. The trained CNN model achieves a defect recognition accuracy of 100% for a one-hour duration, highlighting the importance of not neglecting weak PD signals. This emphasizes the significance of extended measurement duration and pattern saturation in capturing and analyzing weak PD signals for an improved defect recognition. This study contributes to the advancement of practical applications by understanding the behavior of the epoxy material and enhancing defect detection techniques.

Moving Toward Partial Discharge-Free Design of Electrical Machines for More Electric Aircraft Applications

For aerospace electrical machines (EMs), the partial discharge (PD) risk is becoming much more severe due to higher DC link voltage levels and faster switching devices. Traditionally, EMs for safety-critical applications mainly rely on over-engineering methods to guarantee reliability. However, a recent shift towards reliability-oriented design, which is based on understanding the physics of failure, allows for meeting the reliability requirements while ensuring performance. From the perspective of the reliability-oriented methodology, the PD-free design of a starter/generator (S/G) with a 540V DC bus is presented and the main steps for a comprehensive PD risk evaluation are discussed. First, the PD inception mechanism is experimentally investigated under pulse voltage excitation for several rise times, temperatures, and pressure values. Then the measured partial discharge inception voltage (PDIV) values are used to perform an accurate PD risk assessment, which includes the winding hotspot temperature resulting from the S/G mission profile, the environment operating conditions, and the connection cable length. Finally, the PD risk of a S/G with a higher DC bus (i.e., 800V) is examined to comply with the future aircraft voltage level.

Influence of frequency on the partial discharge characteristics of biaxially oriented polypropylene film under nanosecond pulse voltage

Partial discharge (PD) is one of the key factors leading to premature insulation failure of film capacitors used in pulse power devices. To study the effect of frequency on the PD characteristics of biaxially oriented polypropylene (BOPP) film, a sphere-plate electrode was used to simulate defects of the air gap between the film layers. PD experiments of the BOPP film were carried out under 1, 10, 100, 500 Hz, and 1 kHz with a rising edge of 65 ns and a pulse width of 300 ns. The results show that the repetitive partial discharge inception voltage (RPDIV), the number of discharges, the rising stage discharge (RSD) amplitude, and the falling stage discharge (FSD) time-lag, all show an increase and then decrease with increasing pulse frequencies and reach a maximum value at a pulse frequency of 100 Hz. Moreover, the FSD discharge amplitude and the RSD discharge time-lag increase with an increasing pulse frequency. From the perspective of initial electron generation, the quantitative mathematical relationship between PD characteristics (RPDIV, PD amplitude, PD number, and PD time-lag) and frequency was established based on the Fowler–Nordheim field emission effect for the first time, which can reflect the influence of frequency on the memory effect and the development process of PD. The results can provide an experimental basis and a mechanistic explanation for the evaluation of PD characteristics for film capacitors under nanosecond pulse voltage.

Partial Discharge Characteristics and Mechanism of Medium Voltage Power Cable Defects under Different Voltage Stresses

Off‐line partial discharge (PD) diagnosis, which requires an additional power supply has been accepted as an essential step in ensuring the integrity of power cable systems during commissioning testing. Many types of energizing voltage sources (e.g., alternating current resonance, damped alternating current, very low frequency [VLF] sine, and VLF‐cosine rectangular) have been developed, which are used in practice. However, choosing the optimal energizing voltage waveforms for PD testing is still controversial because their capability to motivate PD activities is still unclear. Accordingly, this paper compares the PD ignition capacity of the aforementioned power sources on six well‐designed PD defects in real cable joints. The influence of test voltage frequencies and waveforms are verified. The results show that the PD inception voltage and PD magnitudes in the cable joint defects do not change significantly as a function of the sinusoidal voltage frequency and the VLF‐cosine rectangular voltage exhibits excellent PD ignition capability with a low PD inception voltage and large PD magnitude. Moreover, the dynamic behavior of space charge in a PD defect caused by a gap is analyzed in order to explain the obtained results. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Electrically assisted stereolithography 3D printing of graded permittivity composites for in-situ encapsulation of insulated gate bipolar transistors (IGBTs)

Insulated gate bipolar transistors (IGBTs) find applications in diverse fields, such as integrated motor drives, controllable power systems, and electric vehicles. However, traditional IGBT encapsulation materials are unsuitable for high-voltage applications due to the excessive electric field stress generated at the triple junction; an insulation-enhanced encapsulation material is therefore necessary. Here, using an electrically assisted stereolithography (SLA) 3D printing strategy, we fabricate an encapsulation material with graded permittivity that can uniform the electric field stress distribution in IGBTs. Compared with pure resin and uniform-dispersed BaTiO3-resin composite encapsulation, the graded BaTiO3-resin composite reduces the generated maximum electric field stress (Emax) from 190.2 to 108.3 kV/mm (nearly a 50% decrease). Regarding the partial discharge inception voltage, the devices packaged with graded BaTiO3-resin composite (4.07 kV) also performed better than devices packaged with resin (1.96 kV) and uniform-dispersed BaTiO3-resin composite (2.51 kV). This novel electrically assisted SLA 3D printing strategy will open a new window for the in-situ encapsulation of IGBTs and other microelectronics.

Static breakdown threshold modeling of quasi-uniform gas gaps with a focus on the PDIV of contacting enameled wire pairs

This paper provides a theoretical and conceptual framework for the determination of static breakdown inception thresholds in quasi-uniform gas gaps bounded by dielectric layers of thickness s and relative permittivity . The special case of uncoated metallic electrodes is included in the limit . Moreover, a review of breakdown mechanisms and the underlying physical processes in quasi-uniform gas gaps is provided, and the applicability of the associated breakdown criteria is discussed. The results include a parametrization of the partial discharge inception voltage of wedge-shaped air gaps at atmospheric pressure as a function of the reduced coating thickness . The predicted results for this prototypical insulation geometry agree well with a broad array of literature data and own measurements. Finally, a physically motivated parametrization of the ionization threshold K(d) is suggested for atmospheric pressure air in terms of secondary electron feedback by energetic photons and ion-enhanced field emission. This contrasts with the ad hoc introduction of modified ‘streamer constants’ often found in literature to explain breakdown voltages that deviate from the predictions of the classical Raether–Meek–Loeb criterion.

Comparative Study on Partial Discharge Characteristics of Seven Accessory Defects Under Four On-Site Testing Voltages of a 10-kV Cable Line

Due to the increase in voltage levels and line lengths of power cables, the commonly used alternating current resonance (ACR) voltage is challenging to meet the growth rate of the capacitance of ultra-high-voltage cables for the on-site partial discharge (PD) tests. PD research on power-frequency-like voltages such as damped alternating current (DAC) voltage, very low-frequency sine wave (VLF-Sine) voltage, and very low-frequency cosine rectangular wave (VLF-CR) voltage, has important engineering value for evaluating the cable insulation conditions. In this paper, a PD test and measurement system of a 10 kV XLPE cable line with a 2 km length is established. Seven typical accessory defects are made artificially, including insulation hole, insulation screen tip, ring-cut tool mark, and stress cone installation dislocation defects at the terminals, and connector tip, conductive impurity, and stress cone installation dislocation defects at the joints. PD tests under four kinds of testing voltages of ACR, DAC, VLF-Sine, and VLF-CR are carried out to compare the PD inception voltages (PDIV), phase-resolved PD (PRPD) patterns, and PD location results of various defects. PD equivalence between power-frequency-like voltages and ACR is characterized by PDIV equivalent coefficient <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PDIV</sub> , PRPD pattern characteristic quantities and discharge amplitudes. The results show that DAC and VLF-Sine have an outstanding ability to detect and characterize the severity of PD. DAC and VLF-CR have a good ability to recognize the type of PD. And DAC, VLF-Sine and VLF-CR can accurately locate PD. This study provides an important reference for on-site cable defect diagnosis and PD assessment.

Design of a Flying-Capacitor-Based Voltage Divider LLC Resonant Converter for USB-C PD Charger in Aircraft Applications

Portable electronic devices have grown dramatically at an incredible speed and include many new and sophisticated functions. Thanks to the advent of universal serial bus (USB) power delivery (PD) specifications, power delivery is increased as is the number of applications that can be powered using a USB cable in aircraft. However, the combination of the wide-voltage-gain operation required by the USB PD specification, high step-down ratio, and the lower-pressure environment associated with aircraft puts a lot of stress on converter optimization. This paper presents the DC-DC stage of an integrated, highly compact USB type-C PD charger for aircraft. First, a flying-capacitor-based voltage divider (FCVD) switching bridge is proposed to replace the conventional switching bridge in an LLC converter to improve its efficiency. Second, a printed circuit board (PCB) winding planar transformer is adopted to increase the power density. Gallium nitride devices are used for both the FCVD and the synchronous rectifiers, further shrinking the size and reducing the loss. Critical areas of the converter prone to a high electrical field (E-field) are identified and preemptively addressed with the use of the E-field control methodology that follows the Paschen-curve-based insulation coordination. The prototype is built and tested, and it is verified that the unit successfully operates in rated conditions to achieve a power density of 73.2 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and an efficiency of over 90% at all nominal outputs. A high-altitude partial discharge test is also conducted, showing that the proposed prototype meets the partial discharge inception voltage (PDIV) at 10,000 ft.

Investigating the progression of insulation degradation in power cable based on partial discharge measurements

Assessments of aging and insulation degradation in power components are important to observe and track their condition during operation. Partial discharge (PD) diagnostics is an efficient method for health estimation of the components’ insulation. PD is initiated when the dielectric strength of localized insulation part is decreased. The intensity of PD increases with time, which may lead to insulation failure. This paper investigates the influence of the electrical stresses on the behavior of PD activity in medium voltage (MV) cable containing insulation defects. For this purpose, insulation defects such as internal, surface, and corona are developed in the MV cable environment under laboratory conditions. PD behavior is studied in these defects at gradually increased voltage levels by observing different PD characteristic features including PD inception voltage (PDIV), pulse repetition rate, accumulated apparent charge, average discharge current, discharge power, and quadratic rate. The Tobit regression model is developed for these progressing defects to identify the trends and to predict the behavior based on PD characteristic features. The presented work proposes a framework for the evaluation of the progression of insulation degradation due to increased electrical stress. The study is carried out on XLPE cables, however, the developed approach can be equally implemented on other types of dielectrics and components.