Impulse Breakdown Characteristics Research Articles

Lightning impulse breakdown behavior of natural ester and modified natural ester under long oil gap: An experiment and first-principles simulation analysis

The investigation of lightning impulse (LI) breakdown characteristics in long oil gaps with insulating liquids is of utmost importance for the design of high-voltage, large-capacity transformers. This study focuses on analyzing the negative LI breakdown characteristics of two types of insulating oils, namely high viscosity natural ester soybean oil (SO) and low viscosity modified natural ester palm fatty acid ester (PFAE), under long oil gap conditions. The research includes testing and analyzing the voltage and current waveforms, LI breakdown voltage, and streamer discharge development speed of these liquids across oil gaps ranging from 25 mm to 105 mm. The findings demonstrate that the breakdown voltage of both insulating oils tends to increase as the oil gap distance widens. At a 25 mm gap, the average breakdown voltage of PFAE is not significantly different from that of SO. However, at a 105 mm gap, the average breakdown voltage of PFAE surpasses that of SO by 46.29%. Weibull distribution analysis is applied to the LI breakdown voltage data of the two insulating liquids, resulting in empirical formulas for breakdown voltage as a function of oil gap width at failure probabilities of 1%, 50%, and 90%. The discharge development rate of PFAE is lower than that of SO, especially in the oil gap of 105 mm. With the increase of the oil gap, the streamer development rate of the two insulating oils showed a trend of increasing. Using density functional theory based on first principles, the study investigates changes and discrepancies in parameters such as ionization potential, electron affinity, softness, excitation energy, and molecular surface electrostatic potential of the two insulating liquids with varying electric field strengths. The atomic and molecular scale analysis reveals the primary factors contributing to the contrasting macroscopic lightning shock breakdown characteristics of SO and PFAE. The comprehensive combination of experimental and simulation results suggests that PFAE exhibits greater potential for implementation in high-voltage, large-capacity transformers compared to SO. This study aims to bridge the gap in knowledge regarding the LI breakdown characteristics of different natural esters in long oil gaps. The experimental and theoretical findings presented in this paper provide a foundation for the practical application of natural esters and modified natural esters in high-voltage and large-capacity transformers.

Atomic scale microparameter analysis of modified natural ester molecules related to impulse discharge characteristics under electric field

Modified natural ester (MNE) has significant potential for application in transformers as an environmentally friendly and renewable energy source. In comparison to natural esters, MNE offers notable advantages in terms of viscosity and power frequency breakdown voltage. However, the lightning impulse breakdown characteristics of MNE and the atomic-scale microscopic mechanisms related to its discharge characteristics remain unclear. Understanding the lightning impulse breakdown characteristics of MNE is crucial for ensuring the safe operation of transformers. In this paper, the density functional theory is used to calculate the change law of the microscopic parameters related to the discharge characteristics of MNE under the electric field under the action of electric field, so as to theoretically evaluate the lightning impulse discharge behavior of MNE. The results reveal that the electronic and geometric structures of MNE molecules are influenced by electric fields, which is the primary factor contributing to the variations in microscopic parameters under different electric field strengths. As the electric field intensity increases, the dipole moment of MNE tends to increase, while the ionization potential and excitation energy of MNE tend to decrease. The decrease of ionization potential, excitation energy and energy gap of MNE molecules is about 6.61%–68.01%, 4.34%–47.66% and 2.01%–69.23%. By comparing the calculated results of mineral oil, natural ester, and MNE microparameters, it can be inferred that the lightning impulse breakdown behavior of MNE is similar to that of natural ester and lightning impulse breakdown voltage of MNE is higher than that of natural ester but still lower than that of mineral oil. The average negative polarity lightning impulse voltages of MNE, natural ester and mineral oil in the 85 mm oil gap are about 245 kV, 199 kV and 304 kV, respectively. The test results confirmed the simulation conclusions. This study provides robust theoretical support for understanding the lightning impulse breakdown characteristics of MNE and ensuring its safe operation in transformers.

Effectiveness of Large Soil Grain Sizes in Studying Impulse Characteristics of Soil

There have been many published studies analysing the impulse characteristics of soil and various soil properties. Some of these published results are found to be largely different and inconsistent from one study to another. Soil properties may be complex in nature, and its characteristics under high impulse conditions are influenced by many factors, which result in inconsistency in the results. Nevertheless, it has been known that under high impulse conditions, ionisation in the soil would occur due to air discharges in the air voids within the soil, and interfaces between the soil and the ground electrodes. It is also possible that the expansion of the ionisation zone, leading to the occurrence of breakdown in soil, gives better conduction in soil, producing longer streamers and higher magnitudes of current. However, limited study on the impulse breakdown characteristics of soil is found, which was believed to have been due to voltage/current magnitudes that are not high enough to cause the occurrence of soil breakdown. It is important to determine the factors that will cause breakdown to occur in soil when subjected under high impulse conditions since this will give more effective grounding systems when subjected to high impulse conditions. This paper shows that the soil grain size contributes to the most pronounced factor in influencing the soil characteristics under high impulse conditions, in comparison to any other factors. This paper considers thirty-two soil samples containing various percentages of water contents, subjected to high impulse conditions. The soil samples are housed in a hemispherical environment with two different active electrodes, and pre-breakdown and breakdown characteristics of various soils, configurations and percentage of water content are studied.

Impulse Breakdown Characteristics of Eco-Friendly Gas C₅F₁₀O/N₂ in Nonhomogeneous Field

In this article, the breakdown characteristics of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> O/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixture in a nonhomogeneous field under switching impulse (SI) and lightning impulse (LI) are experimentally studied. The influence of pressure, mixing ratio, voltage waveforms, electric field distribution, and voltage polarity on the breakdown characteristics of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> O/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is analyzed. The results show that: in nonhomogeneous field, the positive breakdown voltage of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> O/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixture appears a “hump” as the pressure increases, and the “hump” of switching breakdown voltage is more obvious. Sulfur-hexafluoride (SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ) outperforms in the breakdown tests, increasing the pressure and the mixing ratio can effectively improve the negative breakdown voltage of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> O/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixture. The breakdown voltages of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> O/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixture change little as the wave tail time changes, while it drops heavily as the electric field nonuniform coefficient increases. The breakdown voltages of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> O/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixture have obvious polarity effect which becomes stronger as the pressure increases.

Negative Lightning Impulse Breakdown Characteristics of Mineral Oil with Different Nitrogen Addition Treatment Methods using Rogowski Electrodes

Negative Lightning Impulse Breakdown Characteristics of Mineral Oil with Different Nitrogen Addition Treatment Methods using Rogowski Electrodes

Impulse Breakdown Characteristics of Transformer Oil with Cellulose Particles in Quasi-Uniform Field

This study presents an experimental comparison of the breakdown characteristics of oil samples with four cellulose particle content levels in a quasi-uniform electric field under lightning impulse voltage. For the experiment to resemble the actual working conditions of transformers and meet the on-site withstand impulse voltage test requirements, both the standard lightning voltage (SLI) and oscillating lightning impulse (OLI) are considered. The experimental results show that an increase in the number of cellulose particles directly weakens the oil insulation strength. At the same particle content level, the oil breakdown voltage under OLI is higher than that under SLI, and the breakdown time lag under OLI is longer than that under SLI. The breakdown time lag is more sensitive to the effect of particle content under SLI. This work is beneficial in deepening the understanding of the impulse breakdown characteristics of transformer oil within cellulose particles and in providing references for the on-site impulse test of oil-immersed power transformers.

Lightning impulse breakdown path and characteristics with dielectric BMC barrier inserted sphere‐plane electrode

This study deals with the electrical breakdown characteristics of the sphere-plane electrode system with the dielectric barrier of bulk moulding compound (BMC) material under the positive lightning impulse voltage. The sphere electrode has a spherical shape of 50 mm in diameter and suspended with a metal rod of 10 mm in diameter, while the plane electrode has a circular with a diameter of 350 mm. The dielectric barrier has a square plate shape of BMC material, and the dimension is changed from 80 × 80 to 240 × 240 mm2. Experimental results show that electrical breakdown paths could be identified into three categories, depending on the dielectric barrier position and the dimension. The larger and farther away from the sphere electrode the dimension of the dielectric barrier is, the occurrence probability of electrical breakdown through the penetration of dielectric barrier becomes. It was confirmed that the breakdown voltage considerably depends on the dimension of the dielectric barrier and the dielectric barrier position.

Lightning impulse breakdown characteristics of SF6 and 20% C3F7CN / 80% CO2 mixture under weakly non-uniform electric fields

This paper provides a comparative study on the impulse breakdown performance of SF 6 and 20% C 3 F 7 CN / 80% CO 2 gas mixture under weak non-uniform electric fields. Two geometrically distinct electrode configurations, with similar field utilization factor, were subjected to standard lightning impulse waveform (1.2/50 μs) and the effects of pressure, gap distance and impulse polarity on breakdown characteristics were studied. The results show that SF 6 has a higher breakdown voltage than the C 3 F 7 CN/CO 2 mixture and the positive 1.2/50 μs breakdown voltages were found to be higher than the negative counterparts. These results show that the effect of polarity on breakdown voltage does not exclusively depend on electrode geometry but also on pressure and gas type. The results of this paper identify the weaker polarity for 20% C3F7CN / 80% CO2 tested with hemispherical rod-plane and coaxial electrode configurations and the results contribute to the design of SF 6 -free gas insulated equipment.

Impulse Breakdown Characteristics of Main Gap in the Presence of a Local Discharge

The characteristics of impulse breakdown voltages and the influence of the position of third electrode in air gap are investigated experimentally to study the parameters influencing the breakdown voltage in the presence of metallic objects around the high voltage power apparatus with air insulation. Experimental results show that the factors affecting the breakdown voltage are the shape and the size of the grounded electrode, the third metallic electrode location and the gap length. A comparison between negative and positive polarities of the applied voltages indicates an important influence of the polarity in the dielectric breakdown mechanism. The possible mechanism by which the local electric discharge initiates the main dielectric breakdown seems to be the high electric field around the local discharge channel and the streamers protruding from its surface.

Impulse-Breakdown Characteristics of a High-Power Gas Switch Based on Graphene Cathode

Graphene has attracted great interest for its distinctive band structure and physical properties. Results from previous studies show that a graphene cathode can provide stable field emission and intense emission in a vacuum. In this paper, a graphene cathode was fabricated using chemical vapor deposition (CVD) on copper electrodes, and the breakdown of the cathode in a high-pressure gas was studied. A low-jitter, self-breakdown gas spark switch based on a graphene cathode is proposed in this paper. The impulse-breakdown characteristics of this switch in a quasi-uniform electric field were studied. When the gap length is 5 mm, and the gas pressure is 0.6 MPa, the average breakdown voltage ( $U_{\mathrm {BD}}$ ) is nearly 85.9 kV, and the voltage jitter is only 3.2%; these values are much lower than those for pure copper cathodes and graphite cathodes. The graphene cathode is found to be a suitable choice for use as a high-power gas switch in applications requiring an intense emission source.

Significantly Improved Electrical Breakdown Strength of Natural Ester Liquid Dielectrics by Doping Ultraviolet Absorbing Molecules

In this paper, we experimentally demonstrate that molecules with maximum absorption wavelength corresponding to the first excitation energy of base liquid molecules are able to significantly improve the electrical performances of natural ester oils. The positive lightning impulse breakdown and acceleration characteristics, ac breakdown characteristics, and streamer structure of the natural ester oils, as well as the electronic properties of the molecules, are presented. The molecules with different absorptions in ultraviolet lights were doped into the natural ester oil. The positive lightning impulse breakdown characteristics of natural ester oil with different doped molecules indicated that the doped molecule with great absorption in the medium wavelength ultraviolet irradiation was able to significantly enhance the positive lightning impulse breakdown and acceleration voltages of natural ester oil by 15% and 60%, respectively. In addition, it also enhanced the ac breakdown voltage by 17%. The base liquid molecules exhibited first excitation energy of 4 eV, which corresponds to the maximum absorption wavelength of such molecules, indicating that the improved electric breakdown strength was a result of the reduced the number of excited molecules and weakened ionization of molecules during the streamer propagation.

Impulse performance of synthetic esters based-nanofluid for power transformer

The lightning impulse breakdown characteristics of a silica nanoparticle based-nanofluid and base oil gaps between electrodes in Type-I and Type-II electrode systems, described in this paper, has been investigated. Based on the analysis of the test results, it has been found that both the mineral oil and synthetic ester oil-MIDEL 7131 based-nanofluid with greater amount of moisture content has higher impulse breakdown strength as compared to its base oil counterparts, with low moisture, in both electrode geometries. Unlike in Type-I electrode system, where there is a linear increase in the enhancement of impulse breakdown strength in nanofluid with nanoparticle concentration level; the enhancement is almost steady in Type-II electrode system, giving an average increase of up to 32% relative to its base oil in the case of synthetic ester while the same is 15% in case of mineral oil, and thus provides interesting possibilities of improvements in the design of insulation structure in ester transformer operating at 400 kV or above. Further, the volt-time characteristics reflect superior performance of nanofluid in withstanding fast events as compared to both base mineral oil and synthetic ester oil. The testing of nanofluid presented, as per the ASTM D3300, for small gap spacing between electrodes considered, will be helpful in assessing the wide scope of the standard in nanofluid research in electric power industry.

Influence of spike defect on the impulse breakdown characteristics of SF6 gas gap in GIS

Influence of spike defect on the impulse breakdown characteristics of SF₆ gas gap in GIS

Trapping and scattering effect of charge carriers on impulse breakdown characteristics of nano‐fluids

Propylene carbonate (PC)-based nano-fluids (NFs), containing only 2 ppm TiO2 nano-particles, exhibit more than 60% higher negative impulse breakdown voltage than that of base liquid. It is found that the resistance of the test gap containing PC remains basically invariable when subjected to high amplitude voltage before the development of electrical breakdown. However, for the NF case, the resistance increases by a factor. Moreover, compared with PC, the streamers in NFs are more complex branched. These experimental results indicate that the charge carriers in NFs can be effectively captured and scattered by nano-particles, which is verified by means of the thermally stimulated current method.

Effect of hydrostatic pressure on the polarity effect of impulse breakdown characteristics of transformer oil

The aim of this study was to clarify the hydrostatic pressure effect on the initiation and propagation process of oil streamers under the application of pulsed voltage with different polarities. The statistical characteristics of the impulse breakdown voltage and time lag in transformer oil were studied over a wide range of hydrostatic pressure, and the statistical time lag and the formative time lag were calculated by the Laue's pattern. The breakdown voltage distribution can be well fitted by 3 parameter Weibull distribution. The results show that the breakdown voltage increases with the hydrostatic pressure for both positive and negative polarity. However, the increase trend is different, linear for the negative polarity and saturated for the positive polarity. At a fixed voltage, when the pressure is increased, the breakdown time increases slightly for the negative polarity, but remarkably for the positive polarity. The statistical time lag for negative polarity is much larger than positive polarity, and the hydrostatic pressure has greater influence for negative polarity. The characteristics of formative time lag are quite different: for negative polarity, it decreases very slightly with the hydrostatic pressure, but increases remarkably for positive polarity. These differences are due to different initiation and propagation mechanisms, which are also discussed in the paper.

Impulse breakdown characteristics of aged oil impregnated paper

Voltage-time (v-t) characteristic plays an important role during the insulation coordination of a power system. Power transformer is the crucial equipment in the design of a reliable power system. During the operation of a transformer, Oil Impregnated Paper (OIP), the widely used winding insulation of transformer, undergoes significant irreversible aging. Aging alters the dielectric properties of the OIP reducing it's withstand capability. Hence in this work, the impulse v-t characteristic of fresh OIP and 8 years service aged OIP of the same manufacturer are compared. Moreover, when the transformers are directly connected to Gas Insulated Substations (GIS) and during the switching operation of vacuum circuit breakers, OIP is stressed by Very Fast Transient Overvoltage (VFTO). In addition, transformers are subjected to repeated impulses generated during multiple lightning strokes, switching operations of circuit breakers and HVDC converters. Various studies have pointed out the adverse effect of VFTO and repeated impulses on transformer insulation. Therefore, the effects of VFTO and repeated impulses (both LI and VFTO) on the v-t characteristics of fresh and service aged OIP are quantitatively assessed and discussed with reference to the Basic Impulse Insulation Level (BIL) and protection level of the transformer insulation.

Preparation of Three Transformer Oil-Based Nanofluids and Comparison of Their Impulse Breakdown Characteristics

Preparation of Three Transformer Oil-Based Nanofluids and Comparison of Their Impulse Breakdown Characteristics

Switching impulse breakdown characteristics of large sphere-plane air gaps compared with rod-plane air gap

With the increase of operation voltage to 800 kV-1100 kV, the sphere-plane gaps with radius of 0.5-1 meter are widely used in the converter station of UHVDC power transmission system. In order to ensure the safety of UHVDC system and reduce the investment, it is necessary to investigate the breakdown characteristic of large radius sphere-plane gap. This paper implemented experiments on three different gap configurations: rod-plane, sphere (R=0.55 m)-plane, and sphere (R=0.75 m)-plane. The 50% breakdown voltages and the current injected into the high voltage electrode were measured. Besides, the discharge process was observed by a high speed CCD camera. Three types of current waveforms related to different streamer progression characteristics were found. With the increase of sphere radius, it can be found that the streamer gradually becomes dominant in the discharge process, which leads to higher average breakdown field, longer streamer length and much more injected charge of first streamer.

Enhancements in the lightning impulse breakdown characteristics of natural ester dielectric liquids

In this letter, we experimentally demonstrate that the lightning impulse breakdown characteristics of natural ester liquids can be significantly enhanced by dispersing molecular additives possessing lower values of both the ionization potential and 1st excitation energies as compared to the base liquid. One such additive contributed to an increase in the breakdown and acceleration voltage of the base liquid by 32% and 90%, respectively. Apart from the expected influence of the low ionization potential of the additives, results also indicate a positive effect of lower value of 1st excitation energy.

A Simple Self-Breakdown Sharpening Switch With Low Jitter and Stable Breakdown Voltage

Normally, a three-electrode spark-gap switch is controlled by the application of an external trigger impulse. In this paper, a novel self-breakdown sharpening switch based on the three-electrode spark-gap switch is proposed. However, in this paper, the trigger electrode is connected to ground through a resistor, with the prespark between the trigger and the main electrodes providing the electrons and ions that initiate conduction of the main gap. A prototype sharpening switch with a breakdown voltage of 116.0 kV ± 1.0 kV and a breakdown time of 3.396 μs ± 0.036 μs is described. When compared with a conventional two-electrode spark-gap sharpening switch, the novel sharpening switch has both a more stable breakdown voltage and lower jitter, and the dc breakdown and impulse breakdown characteristics of the two types of switches are presented and compared. When the impedance of the resistor connected to the trigger electrode is high, it is demonstrated that both the value of this resistor and also the type of load have little effect on the characteristics of the novel switch. However, the breakdown voltage of the novel sharpening switch was found to be sensitive to the rise time of the input pulse from the trigger generator. The prototype sharpening switch has a lifetime at least 20 000 shots and is now in use in a major pulsed power conditioning system.