Partial Discharge Behavior Research Articles

The Effect of Humidity on the AC Breakdown Strength of C₄-FN/CO₂ (5%/95%) and the Partial Discharge Behavior of Corona Under Different Operating Conditions

The Effect of Humidity on the AC Breakdown Strength of C₄-FN/CO₂ (5%/95%) and the Partial Discharge Behavior of Corona Under Different Operating Conditions

Partial Discharge Behavior Prior to Breakdown in Epoxy Resin

To evaluate the deterioration degree of insulation material by monitoring partial discharges (PDs), it is necessary to fully understand the PD behavior prior to breakdown. We performed measurements of temporal variations in the number and magnitude of PDs in a void of epoxy resin. It was found that the number of PDs with larger magnitude is less before breakdown and that there is a decreased tendency of the number and magnitude of PDs with the elapsed time. The tendency is remarkable as the applied electric field is small. Additionally, the time to breakdown becomes short when the scattering of the number of PDs per unit time decreases. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Optimized Fabrication Process and PD Characteristics of MVDC Multilayer Insulation Cable Systems for Next Generation Wide-Body All-Electric Aircraft

For wide-body all-electric aircraft (AEA), a high-power-delivery, low-system-mass electric power system (EPS) necessitates advanced cable technologies. Increasing voltage levels enhances power density yet poses challenges in aircraft cable design, including managing arc-related risks, partial discharges (PDs), and thermal management. Developing multilayer multifunctional electrical insulation (MMEI) systems for aircraft applications is a feasible option to tackle these challenges and reduce the size and mass of cable systems. This approach involves selecting layers of different materials to address specific challenges. Our prior research concentrated on the modeling and simulation-based design of MMEI systems for MVDC power cables. Experimental tests are essential for determining the behavior of PDs under varying pressure conditions. Also, the dielectric strength and time to failure of the designs need to be assessed. In this work, the fabrication process of a down-selected MMEI flat configuration is discussed and analyzed. This paper analyzes the fabrication process of power cables employing MMEI configurations and evaluates the PD characteristics of down-selected ARC-SC-T-MMEI cable samples. This study presents a detailed analysis of the characteristics of PD under atmospheric and low-pressure conditions, which will provide essential insights into the design of MVDC cables for future AEA applications.

Negative Medium-Voltage Direct Current Discharges in Air under Simulated Sub-Atmospheric Pressures for All-Electric Aircraft

The increase in the global temperature due to greenhouse gas emissions is a major concern to the world. To achieve the goal of zero emissions by 2050 in the USA the practical realization of all-electric vehicles, particularly all-electric aircraft (AEA), is important. For the design of electrical power systems (EPSs) in all-electric aircraft, a bipolar medium-voltage direct current (MVDC) system of ±5 kV is being investigated. However, several challenges manifest when using such voltages in a low-pressure environment. One of the main challenges is the partial discharge (PD) behavior of the insulation. It is important to study the PD behavior of the insulation by simulating the aviation environment in the lab. This work aimed to study the partial discharge behavior of air under a negative DC voltage in a needle-to-plane electrode geometry by simulating the aviation pressures in the lab. The partial discharge inception voltage (PDIV) and the breakdown voltage (BDV) show an obvious pressure-dependent variation. Regression analysis was performed to better understand the relationship between the PDIV and pressures. Plots were drawn for the average discharge current at each voltage step until breakdown. This paper’s findings can provide valuable insight into the design of EPS for an AEA. To the best of our knowledge, such a study has not been carried out to date.

Partial Discharge Behaviors Excited by High-Frequency Square Pulse Voltage in Cast Resin Insulation With Thermal-Induced Defect

Partial Discharge Behaviors Excited by High-Frequency Square Pulse Voltage in Cast Resin Insulation With Thermal-Induced Defect

Investigation of partial discharge characteristics in XLPE cable insulation under increasing electrical stress

Insulation degradation in power components is a looming issue that can have a significant impact on the reliability of power system if not attended timely. Partial discharge (PD) diagnostics is a key technique used for the condition monitoring and health assessment of insulation. Inception of PD is a primary indicator which shows degradation and decreased local dielectric strength of the insulation. PD magnitude can increase with time and level of stress, which may result in failure of insulation. This article investigates the behavior of PD characteristics in a medium voltage (MV) cross-linked polyethylene (XLPE) cable sample, containing a defect at the cable termination, under elevated electrical stresses. PD behavior is studied by investigating the key PD characteristics, such as partial discharge inception voltage (PDIV), phase of occurrence (ɸ), mean amplitude (Vmean), pulse repetition rate (PRR), and phase span (ɸspan). These quantities are extracted from a phase-resolved partial discharge (PRPD) pattern using a pulse detection algorithm. Later, these characteristics are analyzed in correlation with the electrical stress. Various regression models are implemented and compared to find the best fit model that represents trending attributes of major PD characteristics. The presented study can be used as an effective process to analyze the measured PD data for evaluation of the insulation condition in the power components.

Characteristics and Mechanism of Partial Discharge Behavior of Power Module Under Unipolar Square Voltage

Characteristics and Mechanism of Partial Discharge Behavior of Power Module Under Unipolar Square Voltage

Effects of Electromagnetic Field on Partial Discharge Behavior in BOPP Film Capacitors

Effects of Electromagnetic Field on Partial Discharge Behavior in BOPP Film Capacitors

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.

Effect of Interplay between Parallel and Perpendicular Magnetic and Electric Fields on Partial Discharges

This paper reports on the influence of a magnetic field on the dynamics of partial discharges (PDs) in two distinct configurations with respect to the mutual orientation of electric fields. The broad application areas include electrical insulation systems of both high-voltage grids and industrial network devices as well as emerging segments such as electric vehicles or more electric aircraft. Traditionally, PD measurements are only carried out in an electric field. In all current-carrying power equipment, magnetic fields are also superimposed onto electric ones, thus influencing partial discharge behavior. It has been observed that the interplay between electric and magnetic fields influences the dynamics of PDs; parallel and perpendicular mutual orientations were specifically investigated. The measurement technique allowed us to quantitively detect the effect of magnetic fields on PDs in a corona point–plane arrangement. The novel element presented in this article is a detection of PD intensity modulated by a magnetic field, with both perpendicular and parallel orientations with respect to electric one, and a quantitative visualization in the form of the time-sequence diagrams. The simulation of electron trajectories in the presence of electric and magnetic fields revealed the elongation of the pathways and differentiation of the charged particle propagation times. The perpendicularly oriented magnetic field led to a twisting effect, whereas the parallel alignment reflected the propagation along a helical trajectory. A slightly stronger PD intensity amplification effect was observed in the case of a parallel alignment of electric versus magnetic fields as compared with the perpendicular orientation. The presented results may contribute to PD measurement methodology in both electric and magnetic fields as well as a better understanding of the underlying physical mechanisms. The observed effect of the modulation of the magnetically based PD dynamics may be relevant for the insulation systems of power equipment.

Electrical Treeing and Partial Discharge Behavior in Epoxy Nanocomposites With In Situ Synthesized SiO2

The electrical treeing resistance of epoxy-SiO2 nanocomposites prepared by synthesizing functionalized SiO2 nanoparticles directly in epoxy was investigated and compared to pure epoxy [diglycidyl ether of bisphenol-A (DGEBA)]. Partial discharge (PD) measurements indicate a transition of initially nonconducting trees to conducting trees in both the pure epoxy and the nanocomposites. A correlation between the synthesis precursors and the PD behavior over time indicates that the presence of ions and remnant precursors hasten the transition to conducting trees and lower the voltage of tree inception. The resistance to tree growth was found to be dependent on the synthesis conditions of the nanocomposites. Slower tree growth was observed in nanocomposites prepared under neutral conditions, with a homogenous dispersion of SiO2 nanoparticles (30–50 nm, 5 wt%). The presence of ions from alkaline conditions and/or poor dispersion of SiO2 resulted in faster and more linear tree growth and lower initiation voltages than for pure epoxy.

Particle-Triggered Corona Discharge Characteristics in Air Insulation Under DC Voltage

Under a dc stress, a wire particle within gas insulation will exhibit complex motion behavior, leading to more challenges to detect its existence. Therefore, this work deals with an investigation of corona discharge characteristics generated from a wire particle with different particle positions in an air gap. Three different wire particles are prepared in this investigation. The particle is placed between parallel-plane electrodes with a fixed gap of 20 mm. Five different positions are evaluated to study the partial discharge (PD) behavior generated from the wire particle. The exponential probability distribution is used to evaluate the pulse occurrences from different positions. Pulse sequence analysis (PSA) technique is employed, and an interpretation algorithm is introduced to understand the discharge pattern. The results show that each of the particle positions creates a unique pattern, which discharge mechanism behind the pattern is explained. From the pattern observation, a wire particle has single cluster of corona type as attached to the electrode while multiclusters are found when it is floating in the gap. Moreover, it is also found that different particle lengths are also affecting the discharge pattern characteristic.

Examination of the Partial Discharge Behaviour Within a Spherical Cavity in Insulation Paper of Transformer

This paper investigates the behaviour of partial discharge (PD) in transformer insulation paper based on the Finite Element Method (FEM). The three-dimensional (3D) FEM model consists of conductor and insulation paper, representing part of a transformer’s high voltage winding. The conductor’s width, height, and length used in this study were 2.4 mm, 11.5 mm, and 16 mm. An insulation paper thickness of 1 mm was modelled around the conductor. An internal cavity with a diameter of 0.5 mm cavity was introduced within the insulation paper. This study introduced two locations of the spherical cavities at the centre and left corner of the insulation paper: Location 1 (L1) and Location 2 (L2). An AC voltage of 33 kV, 50 Hz, was applied to the conductor while the bottom of the insulation paper was grounded. The model was used to study the electric field distribution within the insulation paper and its effect on PD current and charge magnitude. The influence of cavity location on the charge magnitude was also examined. It is found that the electric field distribution is influenced by the conductor configuration as well as the location of the cavity. The electric field in the cavity is the highest at L1 compared to L2. The first PD occurs faster for the cavity with a high electric field. Due to the PD occurrence at the same inception field, the real PD current and charge magnitude is similar at different locations. The apparent PD current and charge magnitude induced at the ground electrode is slightly higher at L1 than at L2.

Corona Discharge Behaviors with Presence of Floating Electrode in Air Insulation using Numerical Model Analysis

This paper deals with numerical analysis method for analyzing the partial discharge behaviors in terms of corona discharge in the presence of a floating electrode under lightning impulse voltage. To analyze the corona discharge behaviors at 0.5 mm short electrode gap system as basic research work between main conductor and floating electrode, we considered fully coupled numerical model based on the charge continuity equations for positively charged ion, negatively charged ion and free electrons. Poisson’s equation is coupled with hydro-dynamic drift-diffusion equations derived from the three kinds of charge continuity equation. Fowler-Nordheim field emission is assumed that the electron emission by electric field is used as boundary conditions for main conductor and floating electrode. As a results, it is found that the floating electrode creates a non-uniform electric field distribution with a large field enhancement, causing ionization to initiate corona discharge. In other words, floating electrode is early corona discharge inception by collecting the induced charge developed by high voltage electrode. This result is expected to be applicable to various corona discharge generating systems as well as insulation design of power apparatus with presence defects such as a floating metal particle under lightning impulse voltage.

An improved technique for quantifying PD activity in cross-linked polyethylene (XLPE) power cables

The presence of air-filled cavities within the insulation of active power cables affects the electric field distribution in the insulation bulk and increases the electrical stress inside and around the cavities. This causes accelerated ageing of the materials and creates regions for partial discharge (PD) development that may subsequently result in cable failure. In this paper, an improved PD quantifying technique applied for insulated power cables is first presented. Its effectiveness is demonstrated through an in-depth study of electric field distribution across a defective cross-linked polyethylene (XLPE) power cable with practical dimensions for HV applications and by analysing the PD behaviour under different ageing conditions. In realizing the aforementioned, the cable model with different arrangements, in series and parallel, of two discharging air-filled cavities was implemented in COMSOL software. The simulated cable fields are analysed for different separations and positions of the cavities before and after PD activity. The cavity fields are extracted in MATLAB and utilized for PD pattern characterization under three ageing conditions. Through the PD patterns and statistical quantities measured from simulated PD behaviour, the severity of PD in the cable model was quantified over the different ageing periods. It was found that the series configuration of the cavities was the most harmful configuration due to its high-field magnitude and greater tendency to initiate a PD propagation. Furthermore, the PD behaviour changes during ageing and the highest PD activity, greater PD magnitude and rate, were recorded at the most advanced ageing stage. Thus, indicating that PD characteristics can be used for inferring the ageing stage.

Effect of energizing voltage frequency on partial discharge characteristics of defects in power cable joints

Power cable joints are the weakest points in a cable system and thus highly susceptible to failure. Partial discharge (PD) events are an important indicator of potential defects in these joints. PD behavior is influenced by not only the geometric configuration of a defect but also by the voltage type and environmental conditions. In this study, several cable joints with four types of common defects were fabricated and their PD characteristics under continuous sinusoidal AC voltages with increasing frequencies were investigated. The variations in the PD inception voltage and maximum PD magnitude we found to be nearly independent of frequency, and the number of discharges per second decreased as the frequency increased. The number and magnitude of PDs in the cable joint defects decreased at a very-low frequency (0.1 Hz) voltage, while those in the frequency range of 10–300 Hz were similar. The presented findings can provide practical support for selecting an appropriate energizing voltage frequency during field testing.

Electrical Treeing and Its Suppression Method of SiR in High Magnetic Field

This paper investigates the effects of high magnetic field on electrical treeing of silicone rubber (SiR). Experimental results show that electrical trees are more easily to be initiated and spread further along the direction of electric field under the effects of high magnetic field. When the direction of high magnetic field is perpendicular to that of electric field, magnetic field with higher magnetic flux density also results in larger accumulated damage area. Splitting of energy band structure and changes in polarization characteristics result in a lower interface barrier and more serious partial discharge, thus causing the weakened resistance to electrical treeing in high magnetic field. Based on the insulation degradation mechanism, SiR was modified by adding ferroferric oxide (Fe3O4) nanoparticles to improve its insulation performance in high magnetic field. Moderate addition amount of Fe3O4 nanoparticles is proved to be able to suppress electrical treeing in high magnetic field by forming quantum dots, modifying polarization properties and partial discharge behavior. Excessive addition of Fe3O4 nanoparticles has negative effects on suppressing electrical treeing due to the magnetization of the nanocomposites.

Condition Assessment of HVDC Cables during their Lifecycle

Recent market developments towards power generation in remote renewable power plants such as concentrated solar power plants in deserts or large off-shore wind parks, raise an interest for long distance power transmission via extruded HVDC cables. HVDC cables require quality assurance during the complete product lifecycle, mainly: a) R&D activities for design verification and - validation b) routine tests in the factory for confirmation of proper manufacturing c) acceptance test after erection and commissioning to exclude defects caused during transport and installation d) ageing monitoring and quick fault detection and location detection during service life. Considering increasing voltage levels, increasing cable lengths and ground or even offshore installation, the dielectric testing of extruded HVDC cables in the factory and on site remains challenging. The long-term validation of insulation coordination requires high voltages for quality assurance tests which represent typical expectable stresses during service. Typical examples are wave shape, partial discharge behavior and dielectric field stress in the insulation medium. Hence, different technical solutions are available to generate these required high voltages for testing of HVDC cables. This paper discusses essential technical and commercial aspects of HVDC cable quality assurance and presents suitable methods for HVDC cable testing.

Long-Term Partial Discharge Behavior of Protrusion Defect in HVDC GIS

This article investigates the partial discharge (PD) behavior of protrusion defects in real-size high-voltage direct current gas insulated switchgear (HVDC GIS) for SF6 and SF6 alternative gases including fluoronitrile–CO2 mixture (10%) and fluoroketone–dry air mixture (6.6%). The evolution of PD apparent charge and PD repetition rate for all investigated gases is presented and discussed. The measurement results indicate that PD behavior changes as a function of time. The PD apparent charge increases and the PD repetition rate decreases with the increase of voltage application time. This evolution can be related to the change in protrusion tip radius due to electrochemical etching: radius of the protrusion’s tip being enlarged. In addition, the pulse sequence analysis (PSA) plots of the PDs caused by this defect are presented. It is observed that the PSA plots change over time. Therefore, for the development of a robust PD monitoring and defect-recognition tool, as well as for the assessment of risks in the operation of HVDC GIS, it is crucial to take these changes into account.

Effect of Magnetic Field on Partial Discharge Dynamics in Insulation Systems of Transportation Power Devices

The globally observed trend toward electrically supplied devices is common in the transportation segment. Traditionally, the performance of electrical insulation has been assessed with respect to electric stresses and endurance. In all current-carrying devices, magnetic fields will also be superimposed on electric ones; therefore, the influence of a magnetic field’s exposure on partial discharge (PD) dynamics is an actual research topic. This problem is important in the transportation segment as well, where low- and medium-voltage levels are mostly used for supply and energy conversion (which are associated with high load currents). This article is focused on the influence of magnetic fields on the dynamics of PDs in the voids of insulation systems of transportation power devices and refers to both ac and dc cases. A rather weak magnetic field (80 mT) was established in order to detect and analyze early stages of PD behavior. The measurements of PDs that were carried out in a dedicated setup revealed their impact on PD intensity, which have been visualized in time-sequence diagrams and PD images. This detected effect is attributed to both the elongation of the charged particle trajectory and the enhancement of the electron energy due to acceleration. It has been shown that the impact of a magnetic field can be observed within a supply voltage frequency range of 20–400 Hz (which is typical for the transportation segment). The PD intensity was amplified in the above range at a magnetic field induction of 80 mT (even up to 50%). The effect of a magnetic field can be recognized as an additional modulation factor that influences the dynamics of PDs.