Discharge Inception Research Articles

Impact of X-Ray Irradiation on Discharge Inception in Gas Insulated Switchgear: A Simulation Investigation

Impact of X-Ray Irradiation on Discharge Inception in Gas Insulated Switchgear: A Simulation Investigation

Performance enhancements of HTS power cables by minimizing the electric field enhancements for electric transport applications

Abstract Design innovations to manage the electric field enhancements and successful use of cryogenic epoxy EP37 as electrical insulation for high temperature superconducting (HTS) cables for electric aircraft applications are reported. Detailed finite element analysis (FEA) of the electric field distribution shows that the highest electric field is at the interface of the ground and electrical insulation layers. The FEA led to the design, fabrication, and experimental characterization of four model cables with stress cones and a direct bond of the ground and insulation layers. Enhanced partial discharge inception voltage (PDIV) was achieved in the model cables by minimizing the electric field enhancements at the ground layer interface. Using a helium gas mixture with 4 mol% H2, with higher intrinsic dielectric strength than pure helium, further enhanced the PDIV. The results warrant further studies on long HTS cables with EP37 as electrical insulation with a direct bond between the insulation and ground layers.

Partial Discharge Inception in Ceramic Substrates Embedded in Silicone Liquid, Silicone Gel, and Mineral Oil at Fast Voltage Rise and Sinusoidal Voltage

Partial Discharge Inception in Ceramic Substrates Embedded in Silicone Liquid, Silicone Gel, and Mineral Oil at Fast Voltage Rise and Sinusoidal Voltage

Pressure scaling laws for partial discharges in wedge-shaped, dielectric-bounded gas gaps

A pressure scaling law for the partial discharge inception voltage (PDIV) of wedge-shaped, dielectric-bounded gas gaps is derived and experimentally validated. The investigated prototypical electrode geometry is of relevance in a number of practical applications, such as contacting enameled wires in electric motors or transformers. The derived pressure scaling law is of particular interest for electric propulsion in aviation systems. The results show that the PDIV can be accurately parametrized from first principles as a function of the scaling parameter p⋅s/εr , where p is the gas pressure, s is the thickness of the insulating coating and ɛ r its relative dielectric permittivity. Previously published empirical relationships between the PDIV and pressure are shown to be local approximations of the presented general scaling law. In particular, the often assumed linear relation of PDIV with pressure is shown to not be generally valid.

Research on Partial Discharge Characteristics of Suspension Defect in GIS under the Action of Voltage and Current

Abstract Gas insulated switchgear (GIS) is a critical component in power system, and the insulation testing is crucial before putting it into operation. Despite passing AC withstand tests, some GIS equipment exhibit insulation faults during operation. Existing AC withstand tests fall short in detecting all insulation faults in GIS equipment. To address this issue, a proposal is made to conduct a comprehensive simulation of actual GIS equipment operating conditions through a combined voltage and current boost test, aiming to address the limitations of existing tests. This study, based on a 330kV GIS test platform, compares the partial discharge characteristics of suspension defects under traditional voltage-boosting mode and the combined voltage and current boost mode. The research investigates the influence of simultaneously applying voltage and current on discharge characteristics. It is observed that the voltage and current boost combined mode significantly increase the partial discharge inception voltage (PDIV) and the corresponding apparent discharge compared to other modes. The apparent discharge quantity after a certain period of current flow during the discharge development process is greater than that observed in other modes. The current notably enhances the ultrasonic amplitude of partial discharge. These findings establish an experimental foundation for conducting voltage and current combined boost tests in the field.

Electrical insulation and dielectric properties of aramid fiber reinforced epoxy composites under mechanical stress

In this work, an in-situ testing platform that could simultaneously apply high voltage (HV) and mechanical stress has been established. The dielectric properties evolution of aramid fiber reinforced composite (AFRC) under different tensile stresses is investigated systematically. The results show that there is a significant influence on the electrical insulation performance of AFRC, when the applied tensile stress reaches 45 % of the ultimate tensile stress (UTS). Elevated tensile stress will induce interface strain concentration inside composites under this condition, which is prone to cause local damage and defects, consequently enhancing charge accumulation under HV. As the tensile stress continues to increase, it is observed that the absorbed charge around defects increases by 49.4 % under 60 % UTS, accompanied by a discernible decline in the partial discharge inception voltage (PDIV) by 46.9 %. With the increase of absorbed charge, the localized intense electric field is formed, thereby fostering partial discharge and breakdown failure. Therefore, it is important to pay more attention to the evolution of dielectric properties of AFRC under mechanical stress in the design and assessment of aramid-based insulation rods. © 2014 xxxxxxxx. Hosting by Elsevier B.V. All rights reserved.

Inception of positive wire-cylinder corona discharges in air in crossed electric and magnetic fields

A computational study of the inception of positive wire-cylinder corona discharges in low-pressure air in crossed electric and magnetic fields is performed. The inception voltages are calculated for a wide range of gas densities, wire radii, and applied magnetic fields. Conditions are considered when the reduced electric fields at wire electrodes reach extremely high values of about 10 kTd. An expression applicable at such strong fields for the ionization coefficient, which is a key parameter of the corona inception model, is presented against the values of electric and magnetic fields. Calculated inception voltages agree with a large quantity of available experimental data on low-pressure positive corona discharges, obtained both with and without the application of magnetic fields. The calculation results describe specific details of the non-monotonous dependence of the inception voltages on the magnetic field values, similar to those obtained in experiments.

AC breakdown characteristics of ultra violet curable epoxy resin with nitrogen fine bubbles

AbstractWe investigated AC breakdown characteristics of ultra violet curable epoxy resin (UV‐EP) with nitrogen fine bubbles (FBs) in order to improve insulating properties of UV‐EP. As a result, it was found that self‐made FB generator mainly add FBs with a diameter between 60 and 150 nm to FB‐EP before curing. In addition, SEM images revealed that FB‐EP has FBs after curing. Bubble diameter in FB‐EP after curing was estimated between 55 and 140 nm due to resin shrinkage. Furthermore, partial discharge inception voltage and electric strength of FB‐EP with FB addition for 10 min were almost the same as No FB‐EP.

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.

Effect of electric field on bubble generation and dissolution characteristics in oil–paper insulation

AbstractThe interturn paper insulation of oil‐immersed power transformer windings, under the combined influence of electric fields, moisture, and conductor heating, will produce bubbles, which pose a significant threat to the insulation system. However, there is limited research on the characteristics of bubble evolution in oil–paper insulation under the influence of electric fields and the subsequent dissolution process. Based on the continuous observation of bubble size using electron microscopes, experimental and theoretical investigations into the formation and dissolution of bubbles under electric field conditions are presented. The effects of different field strengths on bubble evolution and dissolution characteristics were studied. The results showed that the electric field promoted both the generation and dissolution of bubbles, with a more pronounced effect observed at higher field strengths (below partial discharge (PD) inception electric field, hereafter referred to as PDIE). However, when the field strength exceeded PDIE, the bubbles tended to shrink and gradually increase in size. The changes in bubble volume were related to not only gas diffusion but also oxygen consumption and fault gases generation due to PD. A better understanding of the formation and dissolution characteristics of bubbles under varying field strengths is achieved. Furthermore, it also provides a reference for assessing the risk of bubble generation and conducting bubble‐related fault diagnosis during the overload operation of oil‐immersed power equipment.

On the frequency dependence of the PDIV in twisted pair magnet wire analogy in humid air

The partial discharge inception voltage (PDIV) of low-voltage induction motor turn-turn insulation analogy is investigated for variable relative humidity (RH) of the surrounding air (temperature and pressure are kept constant close to their ambient values). Three materials, perfluoralkoxy alkane, sealed and unsealed alumina (UA), are employed as the dielectric coating (insulation) of test samples. Each material’s dielectric properties change differently with RH—of these, relative permittivity is regarded as the most crucial, as it was previously proven to be, along with the coating’s thickness, the key factor in determining the PDIV in dry air conditions. To further vary the value of permittivity and thus provide larger data sets for the verification study, the frequency of the excitation voltage is also varied between 1 Hz and 50 kHz. The obtained experimental data are compared against the PDIV predictions obtained by a breakdown model based on the reduced thickness of the coating (ratio of the coating thickness to its relative permittivity). Satisfying agreement between the measured and predicted PDIV are obtained for the first two materials, whereas significant discrepancies are seen for the UA material. For this case, surface conductivity is introduced into the prediction model and much better fits to the experimental data are obtained for a suitable value of surface resistance. It is hence demonstrated that the model is able to satisfactorily predict the PDIV for three substantially different materials when the RH of the surrounding air is varied between 10% – 80% .

Field Plate Integration for Mitigating Partial Discharge Activity in PCB-Embedded Power Electronic Modules

This paper proposes a concept based on field plate (FP) integration inside printed circuit board (PCB)-embedded power modules. The goal is to reduce the electric field at their surface and thus increase the partial discharge inception voltage (PDIV). Electrostatic simulations are first carried out to analyze the electric field reduction induced by the use of FPs. Then, dedicated experiments are proposed to demonstrate that the actual PDIV increases in AC sinus 50 Hz when FPs are implemented. More specifically, it is observed that an optimal FP length exists. Several analyses based on simulations and experiments are thus proposed to explain this phenomenon. Finally, an assessment of PD activity and PD location is presented to support the analysis. AC sinus 50 Hz characterizations indicate that PDIV can be increased by 178% compared to PCBs without FPs with a proper definition of equipotential prolongation and PCB length.

Enhancing flame and electrical surface discharge resistance in silicone rubber composite insulation through aluminium hydroxide, clay, and glass fibre additives

Silicone rubber (SR) is a leading polymer used in electrical outdoor insulation applications due to its superior hydrophobic characteristics. However, the low flame and electrical surface discharge resistance of SR limit its broad viability and challenge its integrity in severe outdoor working conditions. This work attempts to explore the flame retardancy and surface discharge characteristics of SR co-filled with aluminium hydroxide (ATH), nanoclay montmorillonite (MMT), and chopped glass fibre (GF). Results indicate that the incorporation of ATH/MMT/GF could assist in improving the fire and surface discharge resistance of the SR material. It is noted that the maximum average rate of heat emission (MARHE) and total smoke production (TSP) are measured at 24.93 kW/m2 and 0.48 m2 in SRE, relative to 61.29 kW/m2 and 6.02 m2 in SRB. Using finite element analysis (FEA), the maximum electric field strength is computed at 4.66 × 106 V/m in the air gap coupled with a high-voltage (HV) plate and sample. SRE exhibits a higher partial discharge inception voltage (PDIV) value of 2.32 kVrms than its counterparts, while the maximum discharge magnitude (Qmax) is computed at 7095 pC, relative to 7746 pC in SRB. SRE emerges as a preferable SR composite to be used in electrical insulation applications with excellent flame and surface discharge resistance characteristics.

Derivation of Ambient Enhancement Factors of Impregnated Twisted Pairs for Partial Discharge Risk Evaluation

Partial discharge (PD) is the main issue challenging the electrical machine (EM) insulation system for more electric aircraft (MEA) applications. Indeed, the trend of adopting higher DC link voltage and fast switching device further boost the risk of PD. Partial discharge inception voltage (PDIV) is mostly dominated by ambient conditions (i.e., temperature, pressure, and humidity), and their influence is accounted for through experimentally determined ambient enhancement factors. For non-impregnated windings, ambient enhancement factors are suggested by both IEC 60034-18-41 and recent literature. However, in many applications, EMs’ windings are often impregnated with resin to improve thermal performance, mechanical resistance, and electrical insulation. In this case, no indications of the enhancement factors for PD risk assessment are given. The ambient enhancement factors are experimentally determined in this paper to enable the PD risk evaluation for impregnated windings. These factors are obtained relying on an extensive PD investigation, where PDIV and partial discharge extinction voltage are measured under variable temperature, pressure, and humidity conditions. Finally, the tests are performed on different wire types and motorette samples to validate the applicability of the derived factors.

Determination of Hotspot Temperature Margin for Rectangular Wire Windings Considering Insulation Thermal Degradation and Partial Discharge

Increasing current density is a common way to improve the power density of electrical machines (EMs) which also boosts the winding temperature. Higher winding temperature accelerates the thermal degradation of insulation and also increases the risk of partial discharge (PD). Commonly, the winding hotspot temperature constraint is decided based on an over-engineering approach (i.e., the winding hotspot temperature is 30°C below the wire thermal class) constraining the EM’s performance. In this paper, the margin of winding hotspot temperature is precisely determined focusing mainly on the insulation degradation issues through experimental investigation. The partial discharge inception voltage and partial discharge extinction voltage have been measured under different temperature conditions for samples with different thermal aging statuses. Rectangular wires which find application in automotive motors are selected as test samples. The results link the temperature with the PD risk and the thermal lifetime of the insulation, and the winding hotspot temperature margin is accordingly determined. An automotive case study is presented to prove the applicability of the investigation outcomes.

Study of partial discharge and breakdown phenomena at triple junctions under various conditions of pressure and temperature

The presence of a triple junction constitutes a potential source of failure in many industrial applications. The reinforcement of the local electric field due to differences in relative permittivity facilitates the formation of partial discharges (PD) which weaken the insulation system and eventually lead to complete breakdown. Additionally, severe environmental conditions (temperature, pressure) associated with certain applications (e. g. nuclear or aeronautical sector) should be considered because of their influence on discharge phenomena occurring at triple junctions. In this study, the behaviour of partial discharge inception voltage (PDIV) and of breakdown (flash-over) voltage (BIV) is compared in the case of a triple junction with an aluminium oxide disc as a solid insulator when the system is heated up to 400 °C. While the PDIV decreases strongly for temperatures above 300 °C, this effect disappears for the BIV. It is proposed that this behaviour is due to the fact that relative permittivity of the aluminium oxide disc increases with temperature at low frequencies, but remains relatively stable at high frequencies, regardless of the temperature.

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.

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.

Combined Effect of Short Rise Time and Relative Humidity on the Partial Discharge Inception Mechanism in Rotating Electrical Machines Insulation

Combined Effect of Short Rise Time and Relative Humidity on the Partial Discharge Inception Mechanism in Rotating Electrical Machines Insulation