Impulse Voltage Research Articles

Micro-discharge in GIS/GIL Induced by Scratch Defect on the Surface of Insulation Pull Rods

Abstract The insulation pull rod (IPR) plays a crucial role in gas insulated switchgear (GIS) and gas insulated transmission line (GIL), which must withstand high impulse voltages to cope with frequent switching operations under working conditions. During the manufacturing process, micro-defects may occur on the surface of insulation pull rods, which may cause micro-discharge or even breakdown. It is difficult to carry out experiments to study the microscopic characteristics of the micro-discharge induced by micro-defects on the surface of the insulation pull rod. In order to study the relationship between the micro-discharge and the micro-defects. Firstly, the characterization of the scratch defect based on Micro-CT (micro computed tomography) and white light interference are presented. Secondly, a coaxial DC SF6 corona discharge model is established to obtain the curve related to the density of charged particles in SF6 and the electric field. Finally, we combined the reconstruction of the defect model in the first step with the curve obtained in the second step to simulate the micro discharge around the scratch defect, and provided the micro-discharge in pure SF6 caused by the scratch defect. The phenomenon of micro-discharge induced by the scratch of insulation pull rod is explained. The oscillation phenomenon of internal micro-discharge in scratch defects under high electric field background was discovered.

Breakdown and acceleration voltage of biodegradable liquid made in GTL technology at positive lightning impulse voltage

Breakdown and acceleration voltage of biodegradable liquid made in GTL technology at positive lightning impulse voltage

Degradation of crystalline silicon solar cells caused by lightning induced impulse surge

Abstract Crystalline silicon (c-Si) solar cells are connected in series to form photovoltaic modules, which are installed in wide-open areas. They are exposed to lightning electromagnetic (EM) interference at high risk. The lightning EM field can induce an impulse surge in the loop of the solar-cell string, and c-Si solar cells are prone to damage. To study the effect of lightning surge on monocrystalline silicon cells and polycrystalline silicon cells, impulse voltage tests are conducted. Semiconductor structures of c-Si solar cells after testing are observed using scanning electron microscopy. The results indicate that the lightning surge will generate some cracks and defects in the P–N junction. Under a strong electric field, the N-type emitter layer and the grain boundary can be destroyed, which contributes to the degradation of the c-Si solar cell. Compared to monocrystalline silicon cells, polycrystalline silicon cells can withstand greater forward lightning surge; however, their maximum reverse lightning surge is relatively low.

Discovery of a novel binary azeotrope with positive synergistic insulation strength as eco-friendly SF6-alternative

Abstract Sulfur hexafluoride (SF6), as the arc extinguishing and insulating medium, is broadly applied in power equipment. While it is very essential to find an environmentally friendly substitute gas for SF6 due to its strong greenhouse effect. Although there are many potential alternatives, most have relatively high boiling points that cannot meet the minimum operating temperature of the power equipment. In the past, the liquefaction temperature of the mixture was reduced by mixing with buffer gases, such as CO2, N2, or dry air. But this method cannot take the insulation performance requirements of eco-friendly insulating gas into account. Therefore, given the current problems and challenges, a novel approach is presented to exploring new eco-friendly gases by incorporating the azeotropic theory. The liquefaction temperature of the gas mixture can be reduced simultaneously while the insulation strength is increased. In this approach, a theoretical prediction model E-PPR78 was introduced to predict the vapor-liquid equilibrium data and RC318 was found to exhibit azeotrope behavior with HFO-1336mzz(E) at 17%. Furthermore, the predicted vapor-liquid equilibrium data obtained were validated against cyclic-analytical experimental results, affirming the efficacy of the proposed model. Subsequently, to assess its insulation performance, breakdown tests were conducted under both AC and lightning impulse voltages, revealing significant positive synergistic effects in the gas mixture. The possible mechanisms of this positive synergistic effect were also discussed. This study offers an innovative way of tackling high boiling point issues plaguing eco-friendly gases. The findings may also enlighten the design of eco-friendly switchgear that utilizes HFO-1336mzz(E) mixtures to replace traditional SF6 gases.

Lightning damage assessment on solar panels using in-house portable infrared thermography camera with Convolutional Neural Network (CNN) algorithm

ABSTRACT As the demand for renewable energy sources increases, the vulnerability of solar panels to lightning strikes becomes a critical concern. This research explores the correlation between lightning-induced voltage fluctuations and the resultant damage intensity on solar panels. The study adopts a systematic approach, first investigating the correlation between lightning-induced voltage assessment using 30kV, 60kV and 90 kV impulse voltage with multi-stage Marx impulse generator and the damage intensity on monocrystalline and polycrystalline solar panels. A portable active infrared thermography equipment with tCam-Mini was employed to conduct this research with wireless streaming. Furthermore, the study integrates Convolutional Neural Network (CNN)-based image classification techniques to enhance the efficiency of damage assessment. The results highlight the potential of neural networks in improving the accuracy and speed of image classification for damaged and undamaged samples. The findings contribute valuable insights into enhancing the resilience of solar panel systems against lightning strikes, ultimately advancing the reliability and sustainability of solar energy infrastructure. A new CNN model was developed to classify the images obtained from thermography with 90.21% accuracy for greyscale and 85.31% accuracy on thermal images.

Comparison of Aging Effect of Ester Liquids and Mineral Oil in Semi-Uniform Field Geometry under Lightning Impulse Voltage and Standard Compliant AC Voltage Testing

Comparison of Aging Effect of Ester Liquids and Mineral Oil in Semi-Uniform Field Geometry under Lightning Impulse Voltage and Standard Compliant AC Voltage Testing

Assessing the lightning performance of sustainable GTL type dielectric liquids versus mineral oils and synthetic ester in a non-uniform electric field

This paper presents for the first time the results of complex comparative tests on the lightning performance of a wide range of sustainable electrical insulating liquids made in GTL (Gas-to-Liquids) technology. Three different GTLs are compared with conventional mineral oils (inhibited and uninhibited) as well as biodegradable synthetic ester. Tests are aimed to determine Lightning Impulse Breakdown Voltage (LIBV) and Acceleration Voltage (Va) at standard lightning impulse voltage of both polarities. Those are performed at 25 mm gap distance of point-sphere electrode setup representing non-uniform electric field distribution. In addition, light emission is studied as well. Results show that for the conditions of experiment LIBV values tend to be similar for all tested dielectric liquids with a slight advantage of mineral oils at negative polarity and GTL-I oil at positive polarity. In turn, in terms of Va, it was found that at negative polarity the GTL oils are, in general, fully comparable with a high grade inhibited mineral oil. The Va of GTLs is in the range 260–275 kV versus 255–260 kV that characterizes mineral oils. When considering positive polarity the GTL-I is slightly inferior to other hydrocarbons with Va equal to 195 kV versus 230–255 kV characterizing other GTLs and mineral oils. For both polarities tested synthetic ester has much lower acceleration voltage in relation to hydrocarbon liquids including GTLs, which constitutes a huge disadvantage of the ester. Although the studies are limited to only one gap distance and non-uniform electric field distribution, it can be stated that the GTLs are worth to be examined as alternative to mineral oil when considering LIBV and Va as the analysed quantities. In addition, a special added value of the performed measurements should be mentioned that the measurements confirmed that Va parameter may be a good dielectric indicator of a dielectric liquid performance, especially when examining new product introduced to the market.

Electric Field Features and Charge Behavior in Oil-Pressboard Composite Insulation under Impulse Voltage

Oil-pressboard/paper insulation materials are essential in transformers for ensuring their safe and stable operation, primarily due to their roles in spatial electric field distribution and charge migration mechanisms. Current spatial distribution analyses rely on computational methods that lack empirical validation, particularly for oil-pressboard/paper composites. This study leverages the principles of the Kerr electro-optic effect to develop a rapid measurement platform for electric fields within oil-pressboard/paper insulation under impulse voltage conditions, which measures the spatial electric field characteristics using Cu-Cu and Al-Al electrodes under various scenarios: with asymmetric and symmetric pressboard coverage and different numbers of insulating paper layers. Findings indicated: (1) In asymmetric pressboard models, Cu-Cu electrodes exhibit a consistent peak electric field of approximately 16 kV/mm, while Al-Al electrodes show peak values of 18.13 kV/mm and −14.98 kV/mm. Charge density patterns are similar, with Cu-Cu at about 68 μC/m2 and Al-Al at 11.2 μC/m2 and −124.8 μC/m2. (2) Symmetric models present consistent peak electric fields and charge densities for both polarities. (3) Increasing insulating paper layers elevates electric field strengths. Both electrodes show the similar peak field of about 17 kV/mm with differing paper layers due to higher charge injection from the Al electrode. (4) Utilizing the Schottky effect and field emission principles, the study clarifies charge generation and migration mechanisms. These insights could provide a theoretical foundation for designing and verifying oil-pressboard/paper insulation structures in transformers.

Overvoltage phenomenon initiated by breakdown during on-site withstand voltage tests of GIL and GIS: Mechanisms and consequences

An overvoltage was observed in the withstand voltage tests of GIL and GIS projects in China in recent years. The overvoltage may result in insulation damage and secondary breakdown where there is no defect. The analysis shows that the reason for the overvoltage is the wave impedance discontinuity between the pipeline and the overhead line. It results in the superposition of the reflected and refracted waves, and thus the overvoltage is generated. In fact, in addition to the structural change, the branches in the structure can also form wave impedance discontinuities. For example, unlike GIL, there are many branches in GIS that can also cause the overvoltage. The overvoltage is actually a universal phenomenon. The analyses based on an actual GIS structure show that in on-site withstand voltage tests, the overvoltage may exceed the peak value of the rated lighting impulse voltage, and even the insulation limits of GIS. These analyses are verified by simulation and experiment results. This universal phenomenon seriously endangers the safety of GIL and GIS during the withstand voltage test, because of the possible secondary breakdowns. The GIS will even become more vulnerable. Therefore, the on-site test structures or voltages should be revisited.© 2017 Elsevier Inc. All rights reserved.

Contribution of Metastable Oxygen Spectra to Fluctuated Waveform Tails after Breakdown Time in Air under Positive and Negative Impulse Voltages

In this study, we explored the correlation between fluctuated waveform tails under both positive and negative impulse voltages and their corresponding spectral lines during millisecond observations of arc discharge. We examined impulse voltages in ±100, ±125, and ±150 kV across 3, 3.5, and 4 cm gaps using spectroscopic analysis focused on oxygen excitations. Six selected spectra in ±100, ±125, and ±150 kV at 3.5 cm and two negative spectra of −100 kV at 3 and 4 cm were analyzed by identifying spectral lines in the wavelength range of 200–900 nm. The results revealed a correlation between the fluctuated waveform tails and spectral lines in positive voltage discharges, which were almost similar, while in negative voltage discharges, this correlation was found only in −100 kV at 3 and 4 cm. We concluded that during the spark phase for both positive and negative voltage discharges, symmetrical fluctuation in the waveform tails was observed after breakdown time, especially above the voltage level of the recombination phase. This suggested the presence of energetic oxygen excited states in the 200–400 nm range, with higher peak intensity than the O I line at 777.417 nm, observed in most positive impulse voltage discharges and at −100 kV with 3 and 4 cm gaps, contributing to rapid breakdown.

Observation and analysis of positive leader re-illumination in a 10 m ultra-high voltage transmission line gap under switching impulse voltages

The leader propagation is one of the most important stages in long air gap discharge. The mechanism behind leader re-illumination remains unclear. In high humidity conditions (20.0–30.1 g/m³), we have conducted experiments of long sparks in a 10 m ultra-high voltage (UHV) transmission line gap under switching impulse voltages. The positive leaders predominantly propagate discontinuously, with almost no significantly continuous propagation occurring. The leader channels are intensely luminous and each elongation segment is straight, with streamers resembling the “branch type” which differs from the “diffuse type” streamers at the front of continuous propagation leaders. The distribution of the propagation velocities is highly random (3.7–18.4 cm/μs), and the average velocity (9.2 cm/μs) significantly exceeds that of continuous propagation (1.5–2.0 cm/μs). Analysis suggests that the current-velocity models suitable for continuous leader propagation do not align well with the experimental data in re-illumination mode. Based on the discharge current waveforms and optical images, it is speculated that the newly elongated leader in re-illumination mode does not evolve gradually from the stem (about 1 cm) but rather evolves overall from a thermal channel much longer than stem.

Breakdown Time Phenomena: Analyzing the Conductive Channel of Positive Impulse Voltage Discharges under Standard Temperature and Pressure Air Conditions

Even though the streamer process can be identified in nanoseconds and microseconds through experimental measurements, the breakdown time of air discharge is still unknown. The instability of electrons is suspected to be an attachment-instability phenomenon of the channel conductivity. We investigated breakdown time across milliseconds to better understand how the oxygen excitations of the 200–400 nm range influence a high-conductivity channel even with a weaker applied voltage. Experiments were performed with positive impulse voltages ranging from +42 to +75 kV in the step of +6 kV at a 3 cm gap between needle-to-plane electrodes in a horizontal configuration. A spectrometer with an integration time of 70 ms was used to capture the spectra during voltage discharge. The shortest breakdown time was found at +60 kV with 77 ns compared to +66, +72, and +75 kV. We conclude that the shorter breakdown time at +60 kV is primarily due to the oxygen-excited state in O IV at 262.999 nm. This state helps maintain electron flow by preventing electron loss, with a decay time of 2.5 µs, while releasing Joule heat at a temperature of 26,003 K, which optimizes conductivity. This process occurs before the recombination of the O I line at 777.417 nm, which has a significantly shorter decay time of 27 ns.

Synaptic Response of Fluidic Nanopores: The Connection of Potentiation with Hysteresis.

Iontronic fluidic ionic/electronic components are emerging as promising elements for artificial brain-like computation systems. Nanopore ionic rectifiers can be operated as a synapse element, exhibiting conductance modulation in response to a train of voltage impulses, thus producing programmable resistive states. We propose a model that replicates hysteresis, rectification, and time domain response properties, based on conductance modulation between two conducting modes and a relaxation time of the state variable. We show that the kinetic effects observed in hysteresis loops govern the potentiation phenomena related to conductivity modulation. To illustrate the efficacy of the model, we apply it to replicate rectification, hysteresis and conductance modulation of two different experimental systems: a polymer membrane with conical pores, and a blind-hole nanoporous anodic alumina membrane with a barrier oxide layer. We show that the time transient analysis of the model develops the observed potentiation and depression phenomena of the synaptic properties.

Electromagnetic Compatibility Issues in 400-MHz-Band Wireless Medical Telemetry Systems and Their Management Using Simplified Methods for Safe Operation.

Wireless medical telemetry systems (WMTSs) are typical radio communication-based medical devices that monitor various biological parameters, such as electrocardiograms and respiration rates. In Japan, the assigned frequency band for WMTSs is 400 MHz. However, the issues accounting for poor reception in WMTS constitute major concerns. In this study, we analyzed the effects of electromagnetic interferences (EMIs) caused by other radio communication systems, the intermodulation (IM) effect, and noises generated from electrical devices on WMTS and discussed their management. The 400-MHz frequency band is also shared by other radio communication systems. We showed the instantaneous and impulsive voltages generated from the location-detection system for wandering patients and their potential to exhibit EMI effects on WMTS. Further, we presented the IM effect significantly reduces reception in WMTS. Additionally, the electromagnetic noises generated from electrical devices, such as light-emitting diode lamps and security cameras, can exceed the 400 MHz frequency band as these devices employ the switched-mode power supply and/or central processing unit and radiate wideband emissions. Moreover, we proposed and evaluated simple and facile methods using a simplified spectrum analysis function installed in the WMTS receiver and software-defined radio for evaluating the electromagnetic environment.

Study on the Design of Valve Base Insulation and Power Supply Transformer for High-Voltage DC Circuit Breaker

Abstract High-voltage DC circuit breaker is a key piece of equipment to building DC power grids. DC circuit breakers need to support and isolate from high voltage to ground through valve-based equipment and use valve-based power supply transformer to continuously supply energy to high potential components, the electrical performance of these two equipment determines whether DC circuit breakers and DC networks can be operated safely and reliably. For this reason, this paper carries out the research on the insulation capability of the valve base and the performance of the power supply transformer, such as the design and simulation of electric and thermal fields, as well as the test program. Firstly, the insulation design and simulation study of the valve base as a whole is carried out, and the design optimization of the equipotential scheme of the top homogeneous tubular bus, diagonal pull insulator and hydroelectric pole is completed. Secondly, the design and simulation verification of the thermal field distribution of the energy-supply transformer, the overvoltage between the ends of the output windings and the optimization scheme, and the short-circuit impedance were carried out. Finally, the insulation performance of the valve base, the temperature rise of the energy supply transformer, the overvoltage simulation of the output winding and the short-circuit characteristics were tested. The results show that: after optimization, the maximum field strength of the homogenizer is 2.3kV/mm, and the overall maximum field strength of the valve base is 2.61 kV/mm on the diagonal insulator, and there is no pressure difference between the water circuit and the fittings using the three-pin vertically distributed hydropower electrode scheme; the temperature rise of the supply transformer in the simulation and the actual measurement is 27K and less than 30K; by means of the parallel connection of the MOV, the overvoltage of the output winding of the power supply transformer under voltage impulse is effectively reduced to -1.8kV; the measured short-circuit impedance of the power supply transformer is 69.5%. The optimized design of DC circuit breaker valve base and power supply transformer can operate safely, and effectively support the construction of DC circuit breaker and DC power network.

Improvement of AC Conditioning Effect in Vacuum by High Frequency Voltage

To improve the dielectric strength in vacuum, spark conditioning through repetitive breakdowns by AC or impulse voltage is an effective method. AC conditioning at commercial power frequencies has been widely used due to its cost‐effectiveness, but the breakdown voltage after AC conditioning is generally lower compared to impulse conditioning. We have confirmed that multiple breakdowns occur successively in a half cycle of AC voltage application. It is considered that the multiple breakdowns are harmful for conditioning and triggered due to the previous breakdown in the same half cycle. In this paper, we discuss dielectric strength improvement by high frequency AC conditioning and how the multiple breakdowns are induced. We experimentally confirmed that the AC conditioning effect is improved by increasing the frequency of AC voltage for different applied AC conditioning voltages in a sphere‐plane electrode system. We focused on the breakdown position from the light emission images during AC conditioning to investigate whether the multiple breakdowns were induced or affected by the previous breakdown. We found that the multiple breakdowns occurred close to the previous breakdown position. The multiple breakdowns would be induced by the collision of metal particles due to the previous breakdown with the counter electrode. These breakdowns do not contribute to removing protrusion and would lead to damage to the electrode surface. The increasing frequency of AC conditioning would suppress the multiple breakdowns and improve the dielectric strength in vacuum. © 2024 The Author(s). IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Simulation of breakdown voltage associated with phase-to-phase air gap for ultra high voltage transmission lines under switching impulse voltage

Abstract Knowledge of the breakdown voltage of air gaps when subjected to positive switching impulse voltage is fundamental to the design of insulation coordination for power transmission systems. However, the length of phase-to-phase air gaps in ultra-high voltage power transmission lines has reached more than 30 m. It is very difficult, costly, and impossible to conduct full-scale test experiments to obtain the breakdown voltage of these gaps. Here, the numerical simulation method based on the self-consistent leader inception and propagation model was first used to simulate the air gap discharge process at four different scales and to obtain the gap breakdown voltage. The simulated data was compared with the measured data to verify the validity of the model. Then, the numerical simulation method was used to simulate the discharge process of phase-to-phase air gap for ultra-high voltage transmission lines with 30.3 m in length. The current and the development trajectory of the leader tip were obtained for the discharge process. More importantly, the breakdown voltage, which could not be obtained by full-scale testing, was obtained by simulation.

An Analysis of Positive Switching Impulse Voltage and negative streamer growth in point-sphere gap towards Valve Hall

An Analysis of Positive Switching Impulse Voltage and negative streamer growth in point-sphere gap towards Valve Hall

Ultrahigh energy efficiency from a supersonic underwater ultrasound source

The present work is dedicated to an experimental and theoretical study of an innovative underwater ultrasound source. The source works using a technique in which a pulsed power generator using the impedance mismatch of a long high-voltage coaxial cable generates a train of voltage impulses with a very high pulse repetition frequency of the order of a few MHz. Applying this train of voltage impulses to a pair of underwater electrodes generates a streamer-initiated breakdown of water and, subsequently, a plasma column connecting the electrodes over a very large inter-electrode gap of 55 mm. The interaction of the long plasma column thus formed with the surrounding water produces a rapidly expanding vapor bubble, an “instrument” producing a strong pressure wave with an overall energy efficiency of 24%, an order of magnitude higher than most underwater pressure sources reported in the literature.

Breakdown characteristics of HFO1234ze(E)/N2 gas mixture in non-uniform electric field under lightning impulse voltage

Breakdown characteristics of HFO1234ze(E)/N2 gas mixture in non-uniform electric field under lightning impulse voltage