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Due to rapid temperature rise and insulation moisture, bubbles can generate in the oil-paper insulation of oil-immersed power transformers, which can reduce the dielectric strength of oil-paper insulation and even bring about the risk of insulation breakdown. In order to accurately evaluate the conditions of bubble formation, the physical process of bubble formation in oil-paper insulation is studied in this article. Considering the effects of water vaporization, gas dissolution in oil, and moisture migration on bubble formation, a bubble formation prediction model is constructed. Based on Henry’s law, the dissolution equilibrium of gas in oil is taken into consideration and the upper boundary of the initial temperature of bubble effect (ITBE) envelope is obtained in this model. Based on the moisture equilibrium in oil-paper insulation, the bubble formation process caused by the emergence and rapid evaporation of free water is analyzed, and then, the lower boundary of the ITBE envelope is obtained in this model. The model results show that the moisture content of the pressboard and the presence of free water have a great impact on ITBE. Specifically, the higher the moisture content, the lower the ITBE value. In addition, with the further increase of moisture content, the upper and lower boundaries of the ITBE envelope gradually tend to be the same. However, once free water is present on the surface of cellulose, ITBE decreases rapidly to below 120 °C. The model built in this article is of great significance to study the temperature limit of the power transformer. Hence the ITBE envelope can provide an important theoretical reference for reducing the risk of bubble formation during power transformer operation. [ABSTRACT FROM AUTHOR]

Bubbling phenomenon usually arises from overheated cellulose insulation in oil, which is known for deleterious effects on the insulation strength of oil-immersed transformers. In this paper, the experiment was conducted on a self-heating conductor wrapped with insulation paper. The inception temperature of bubbling phenomenon negatively correlates to the rising rate of temperature and moisture content of paper, which is in accordance with the results of previous research. Besides, bubbles formed under different conditions could be different in morphology and locations. Thereafter, a method for temperature rise was proposed, based on which the models were heated for component research. It is found that the component changes in oil and blanket gas are significant in a short time interval under bubbling conditions. Comparison trials were then conducted on naked conductors and paper-wrapped conductors. Based on the theory of mass transport, it is revealed that the water vapor and carbon oxides contribute a major part in bubble composition, and their proportions vary with the bubbling temperature. This study concludes that bubbling phenomenon at temperature below 120 ?C can be recognized as the vaporization of moisture in paper. Moreover, bubbles formed at temperatures around 160 ?C can be attributed to the combined effect of water vaporization and gases from cellulose degradation. [ABSTRACT FROM AUTHOR]

Sulfur corrosion has been proven to significantly decrease the insulation performance of oil-immersed transformer and the addition of benzotriazole passivator (BTA) to insulating oil has been widely used to control the sulfur corrosion. However, the relevant studies indicate that the addition of metal passivator to oil can cause abnormal generation of dissolved gases in oil. Thus, this study further explores the effects of metal passivator degradation on the dissolved gas characteristics of oil in oil-immersed transformers. Several accelerated aging experiments on oil-paper insulations with and without BTA are conducted. The results indicate that the addition of BTA lead to the generation of abnormal dissolved gases in the oil along with an increase of stray gases, especially the increase of H 2 , CO and CO 2. Moreover, an abnormal production of the total hydrocarbon fraction is found, which may interfere with the DGA results. Finally, the degradation of BTA related to abnormal production of stray gases in the insulating oil was preliminarily analyzed and discussed. [ABSTRACT FROM AUTHOR]

The power transformer is one of the most important equipment in the electrical power system due to its cost and potential failure????s consequences. To ensure a continuous energy supply, it is needed to assess abnormal condition such as thermal and electrical behavior. From this viewpoint, dissolved gas analysis (DGA) is very useful in detecting internal defects in oil-filled electrical equipment. A system has been developed that allows to simulate partial discharge and overheating in transformer????s insulation. By using this system, we have studied on DGA under low temperature overheating in mineral oil and vegetable oil. [ABSTRACT FROM AUTHOR]

In this paper, a series of laboratory experiments are conducted to investigate the effect of momentary small variations in the transformer operating temperature on the dissolved gas analysis (DGA) measurement. With the increased penetration level of renewable energy sources of intermittent characteristics into electricity grids, operating power transformers are expected to experience frequent temperature variations. Sampling transformer oil during such temperature variation leads to inaccurate diagnosis. Experimental results reveal that gas evolution in transformer oil is greatly affected by the small variations in the operating temperature. Such small variation can be a result of the intermittent generation characteristics of renewable energy sources. Hence, false analysis may be reported if oil is sampled during generation or load fluctuation events. Experimental results are explained through chemical equilibrium constant theory, which indicates that dissolved gases reflect the change in aging rate of the transformer oil-paper insulation system. These results suggest a new paradigm for DGA process through correlating measurements with the transformer operating temperature through the generation and load profiles at the instant of oil sampling. [ABSTRACT FROM AUTHOR]

Dissolved Gas Analysis (DGA) is a well established method to monitor and predict the condition of devices with oil-cellulose insulation, especially power transformers. However, the effect of the migration of theses gases between the liquid and solid insulation is often ignored. The migration phenomenon is temperature dependent and, if ignored, can potentially lead to erroneous condition assessment by the DGA method. This paper addresses the dynamic nature of propagation of these gases in such systems based on temperature variations. Diffusion times, and therefore diffusivity of the gases, in oil-impregnated cellulose are calculated by identifying the diffusion process as a linear system. The diffusion time-constants, and steady-state condition at the working concentrations, are estimated based on the identified model. A sensitivity study is performed to show the dependency of the diffusion time-constants to the temperature and the oil-cellulose ratio in the system. The equilibrium curves are obtained in the case of carbon dioxide by using solubility information of this gas in the oil and paper pulp, similar to the case of moisture equilibrium. The results are compared with the experimental data. An example of the implication of the obtained data is shown. [ABSTRACT FROM AUTHOR]

As vegetable insulating liquids have different chemical compositions from mineral oils, dissolved gas characteristics under thermal and electrical faults have differences; thus fault diagnostic methods based on dissolved gas analysis (DGA) used for mineral oil-filled transformers may not be suitable to vegetable oil-filled transformers. This paper presents experimental results of dissolved gases in Camellia insulating liquid under typical thermal and electrical faults in transformers. Thermal fault simulation experiments include three parts, which are low temperature, medium temperature and high temperature faults, and the electrical fault simulation experiments also include three parts, which are partial discharge, breakdown discharge and arc discharge. Experimental results show that apart from CO and CO 2 , H 2 and C 2 H 6 are the main characteristic gases under thermal faults, and the percentage of H 2 decreases while CH 4 , C 2 H 4 and C 2 H 6 increases with temperature. In addition, H 2 and CH 4 are the main characteristic gases under partial discharge faults; C2H2 is the main characteristic gas under breakdown faults, and C2H2 and C2H4 are the main characteristic gases under arc discharge faults. Furthermore, graphic fault diagnostic methods based on DGA of Camellia insulating liquid including Triangle and Pentagon diagnostic methods are proposed. Compared with the current diagnostic method, the proposed methods in this paper have higher diagnostic accuracy. [ABSTRACT FROM AUTHOR]

This paper investigates the AC insulation properties and explores the influence of electric field inhomogeneity on the breakdown voltage of HFO-1336mzz(E)/CO 2 gas mixture. The electrical field sensitivity of HFO-1336mzz(E)/CO 2 and SF 6 is further compared. It is found that the insulation performance of HFO-1336mzz(E)/CO 2 mixture with 25–30% HFO-1336mzz(E) can reach up to 75-85% of SF 6 under the quasi-uniform electric field and there is a favorable positive synergistic effect between HFO-1336mzz(E) and CO 2. The breakdown voltage of HFO-1336mzz(E)/CO 2 gas mixture demonstrates a “hump” effect with gas pressure under the highly non-uniform electric field and its sensitivity to the electric field inhomogeneity is significantly lower than that of SF 6. The insulation performance of HFO-1336mzz(E)/CO 2 with HFO-1336mzz(E) content higher than 20% reaches 0.99–1.05 times that of SF 6 under highly non-uniform electric field. The AC breakdown voltage of HFO-1336mzz(E)/CO 2 gas mixture and SF 6 decreases first and then increases with the electric field inhomogeneity (f), demonstrating a “U-shaped” like curve and finally tends to be stable. The related results of this paper systematically reveal the AC insulation properties of HFO-1336mzz(E)/CO 2 gas mixture and provide an important reference for its engineering application. [ABSTRACT FROM AUTHOR]

Dissolved gas analysis (DGA) is widely accepted as an effective technique to detect incipient faults within power transformers. Gases such as hydrogen, methane, acetylene, ethylene and ethane are generated as a result of insulation oil decomposition, while carbon monoxide and carbon dioxide are generated as a result of insulation paper decomposition. Laboratory-based gas chromatography (GC) in accordance to ASTM D3612 standard is globally accepted as a reliable technique to quantify dissolved gases in transformer oil samples. However, this technique incurs running cost and requires an expert to conduct the test. Furthermore, due to the complexity of the equipment, measurement is only performed in a laboratory environment and takes long time to get the results since the extraction of the oil sample from the transformer. To overcome these issues, various online DGA techniques have been developed and currently used by industry. However, these techniques are still considered in development stage with some limitations that have to be addressed to fully accept its results. This paper proposes a new method to estimate the concentration of various dissolved gases in transformer oil using near infrared-to-infrared (NIR-IR) spectroscopy that can be conducted instantly onsite with relatively inexpensive equipment. The proposed measuring technique does not call for expert person to conduct the measurements and has the potential to be implemented online. Results show a good correlation between oil spectral response and the concentration of each dissolved gas in the oil at particular wavelength range. Fuzzy logic model approach is employed to model this correlation and estimate the concentration of each dissolved gas. [ABSTRACT FROM AUTHOR]

This paper reports on an investigation into the surface flashover of an insulator in a C4F7N/CO2 mixture which is used as an alternative to SF6. To date, no studies on this aspect have been reported in the literature. This study was done for a uniform field using a 220 kV AC experimental platform. The influence of molar fraction, gas pressure and creepage distance is reported and compared to that in SF6. The results show that small quantities of C4F7N mixed in CO2 can increase the surface flashover voltage but, as the fraction of C4F7N increases, saturation of the surface flashover occurs. The relative surface flashover voltage of 13.0% C4F7N/87.0% CO2 is approximately 80% that of SF6. The empirical formulae on the critical flashover electrical field has been obtained, which may be referenced in the design of environment friendly high voltage equipment. [ABSTRACT FROM AUTHOR]

Transformers are vital components of power systems as they are situated between energy generation and consumers and their failure disrupts the use of electrical energy. Therefore, diagnosing an incipient fault is essential in avoiding hazardous operating conditions and minimizes downtime cost. In transformers, faults take place due to electrical or thermal stresses that cause insulation decomposition in transformers. In oil-filled transformers, insulations are cellulose and oil, and the products of the insulation decomposition are gases which can be dissolved in the oil. Therefore, dissolved gas analysis (DGA) can be used for fault diagnosis in oil filled transformers. In this paper, DGA interpretation methods, conventional and intelligence, are investigated and compared. For evaluating consistency and accuracy of the methods, "No Result" cases are not considered. It can help the newcomers to this field to have access to a comprehensive comparison about the application of computational intelligence and conventional methods in transformer fault detection using DGA. [ABSTRACT FROM AUTHOR]

In this paper, the synergistic effect of CF3I mixed gas is theoretically analyzed using the Boltzmann method and experimentally studied under different applied voltage, pressure and electric field inhomogeneity. The experimental results show the inversion of synergetic effect, which reflects the influence of external conditions on synergetic effect. The results show that CF3I/N 2 and CF3I/CO2 mixtures under slightly uneven electric field at normal pressure have synergistic effect. CF3I/CO2 mixtures under power frequency voltage and lightning impulse have better synergistic effect than CF3I/N2. The effect of macro parameters on synergetic effect is different for different buffer gases. For CF3I/N2 mixture, the synergistic effect of the mixture can be improved by increasing the pressure and increasing the electrode gap distance. For CF3I/CO2, due to the abnormal breakdown of the mixture, negative synergistic will occur at some pressure and gap distance. [ABSTRACT FROM AUTHOR]

Dissolved gas analysis (DGA) of insulating oil can provide an important basis for transformer fault diagnosis. To improve diagnosis accuracy, this paper presents a new transformer fault diagnosis method based on deep belief networks (DBN). By analyzing the relationship between the gases dissolved in transformer oil and fault types, the Non?code ratios of the gases are determined as the characterizing parameter of the DBN model. DBN adopts multi-layer and multi-dimension mapping to extract more detailed differences of fault types. In this process, the diagnosis parameters are pre-trained. A back-propagation algorithm adjusts them with the labels of the samples and optimizes the parameters. To verify the effect of the proposed method, the diagnostic DBN model is constructed and tested using various oil chromatographic datasets collected from the State Grid Corporation of China and previous publications. The performances of the DBN diagnosis model are analyzed by different characterizing parameters, different training datasets and sample datasets. In addition, the influence of discharge and overheating multiple faults on the diagnosis model is studied. The performance of the proposed approach is compared with that derived from support vector machine (SVM), back-propagation neural network (BPNN) and ratio methods respectively. The results show that the proposed method significantly improves the accuracy of power transformer fault diagnosis. [ABSTRACT FROM PUBLISHER]

Basin insulators in gas insulated switchgear (GIS) are prone to failure by partial discharge (PD). Insulation diagnosis using gas analysis method has advantages of strong anti-interference ability and high detection precision. This paper reports a new characteristic gas Carbonyl Sulfide (COS) for the detection of PD in epoxy insulators of GIS. The generation of COS is verified by experiments with trace gas detection technique. Experimental results indicate that COS is generated only when the intensity of PD is strong enough to cause flashover on the epoxy insulators. The corresponding production mechanisms of COS have been clarified using quantum chemistry calculations. To assess the PD level using COS, the relationship between discharge power and growth law of the concentration of COS is obtained from the experiments, which indicates that COS could be used as an effective characteristic gas to diagnose epoxy solid insulation of GIS concerning high energy discharge. [ABSTRACT FROM PUBLISHER]

This paper is aimed at the breakdown characteristics of Fluoronitriles ? CO2 gas mixtures in different experimental conditions; these mixtures constitute promising substitutes to SF6 gas in high voltage applications especially gas insulating switchgear (GIS). Fluoronitriles chemical gas compound based on 3M NOVEC 4710 have a high dielectric strength, more than 2 times that of SF6 and a low Global Warming Potential (GWP). Mixed with CO2 as gas carrier, the obtained mixtures offer interesting dielectric properties and the possibility to be used for low temperature applications. The experiments are conducted with different electrodes geometries namely plane-to-plane, sphere-to-sphere, sphere-to-plane and rod-to-plane (i.e. in homogeneous, quasi-homogeneous and inhomogeneous electric field distribution) and different field utilization factors, under AC and lightning impulse voltages. The same experiments are reproduced for pure SF6 for the comparison. The comparison of breakdown voltages results of mixtures with different concentrations of Fluoronitriles in CO2 in sphere-to-sphere electrodes arrangement shows that the 3.7 % Fluoronitriles / 96.3% CO2 mixture constitutes a good compromise and an appropriate gas mixture for high voltage apparatus insulation in point of view of pressure and low ambient temperature application (-30°C). [ABSTRACT FROM AUTHOR]

Potential substitutes for SF 6 such as fluoroketone (C 6 F 12 O and C 5 F 10 O) and fluoronitrile (C 4 F 7 N and C 3 F 5 N) gases have been widely studied. The electron impact ionization cross section (Q ion) is the key parameter in the simulation of gas discharges. Moreover, the Q ion can be used in the preliminary screening of large scale alternatives of SF 6. In this paper, the Q ion of C 6 F 12 O, C 5 F 10 O, C 4 F 7 N and C 3 F 5 N are calculated via the BEB method. The orbital parameters are obtained by M⊘ller-Plesset perturbation function with second order approximation (MP2), which is validated by comparing the theoretical and experimental Q ion for CH 3 CN, CF 3 CN, C 2 H 4 O, C 3 H 6 O and C 4 H 8 O. The linear relationship between the maximum Q ion and polarisability supports the validity of the BEB method with MP2 function, which suggests that the results of the calculated maximum Q ion for C 5 F 10 O and C 4 F 7 N are reasonable by BEB method. Lastly, the correlation between the maximum Q ion and E r is discussed. The analysis shows that there is a correlation between the maximum Q ion and E r , and the correlation coefficient reaches 0.598. It is thought that Q ion can be as a new predictor to estimate the dielectric strengths for SF 6 replacements. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) in gas insulated switchgear (GIS) has been studied extensively under AC voltage or transient voltage applied alone. However, the transient voltage in an actual system is superimposed on the AC operating voltage, which has rarely been studied. In this paper, the effect of AC and switching impulse superimposed voltage on PD characteristics was studied in SF6 gas. A test platform of generating superimposed voltage with controllable phase was used to study free particle and floating potential defect models. When the AC voltage was 90 and 110% of PD inception voltage (PDIV), the standard switching impulse with amplitude of about twice the PDIV was superimposed on different phases of the AC voltage. When the AC voltage is below the PDIV, results show that PDs of free particle defect model can be initiated when switching impulse is superimposed on 45 and 90° of AC. The PDs in the subsequent cycles of AC reignited into a self-sustaining discharge. For the floating potential defect, PDs have a marked difference duration, which is initiated by switching impulse in different phase. However, there is no change in PDs in each model when the AC voltage is above the PDIV. [ABSTRACT FROM AUTHOR]

The paper focuses on the factors that lower the dielectric performances of real-size gas insulated systems, and show the examples of the measures by using dielectric coatings. The factors studied in this paper are area effects of electrodes and metallic particle motion which are now dominant to determine the size of gas insulated switchgear (GIS). The gases for the systems are basically SF6 but potential gases like N2/SF6 gas mixtures, CO2, dry air and N2 are also included. Area effects of electrodes are studied by reviewing the minimum breakdown data at lightning impulse (LI) of large effective electrode area over about 5 x 104 mm2 under high gas pressures up to 1.9 MPa. The breakdown electric field strength (BDE) or breakdown voltage (BDV) is normalized by the theoretical value and evaluated in terms of effective electrode area and gas pressure. Under the same gas pressure in the range between 0.2 and 0.7 MPa at negative LI, the normalized values of SF6 are lower than those of the potential gases which show similar values. However, the normalized BDVs of N2 at positive LI are further lower than those of SF6 at negative LI. The advanced dielectric coatings enable high dielectric performances over 80% of the theoretical values in SF6 and CO2. Concerning the second factor, metallic particle motion, the experimental data of metallic particle levitation and crossing to high voltage electrode are gathered for dielectric coated and bare enclosures in SF6, N2/SF6> and dry air. The data are classified into two cases of with and without mechanical impulsive force to the enclosure, which simulates the force by the operation of circuit breakers, disconnecting switches and earthing switches. The particle lift-off/levitation electric field strength on the inner surface of dielectric coated enclosure is about 2 to 11 times higher than that on bare enclosure without a mechanical vibration. With a mechanical vibration, the particle lift-off/levitation and crossing electric field strength on dielectric coated enclosure decrease but still about 2 to 3.5 times and 1.3 to 1.6 times higher than those on bare enclosure, respectively. [ABSTRACT FROM AUTHOR]

The effect of electronegative gas on the insulation characteristics of mixed gases as alternatives to SF6 has widely been investigated to identify an appropriate insulation medium and to develop SF6-free high-voltage power equipment (HVPE). However, few studies have provided physical information on the surface discharge mechanism and physics of gas discharge to clarify this effect. This paper presents the surface discharge characteristics of SF6 and imitation air (I-Air), i.e. N2/O2 mixed gas, under a nonuniform field, and focuses on their characteristics in relation to the oxygen concentration in N2/O2 mixed gas. According to experimental results, the insulation characteristics of I-Air, especially the surface flashover voltage, decreases with increasing O2 content, when over 20% in the N2/O2 mixed gas. These characteristics are explained by the proposed surface discharge mechanisms including photoionization, electron detachment, and photoemission in accordance with changes in the O2 concentration in the N2/O2 mixed gas. In addition, the surface insulation performance of I-Air corresponding to 0.1 MPa SF6 is examined. [ABSTRACT FROM AUTHOR]

In this paper, the basic lighting impulse breakdown performance of trifluoroiodomethane and nitrogen mixture with a volume ratio of 20% CF3I - 80% N2 under 7 bar absolute gas pressure has been investigated. The 50% lighting impulse breakdown voltages (U50) of three types of electrode gap were measured to investigate the dielectric behavior of the gas mixture. The maximum breakdown field strengths (Emax) have been calculated to evaluate the influence of the electrode gap, which can be used to estimate whether breakdown occurs. At the same time, the characteristics of pure sulphur hexafluoride (SF6) and 20 % SF6 – 80% N2 gas mixture have been studied for a comparison. In order to evaluate the potential of CF3I-N2 mixture to replace SF6 in high voltage equipment, a metal enclosed gas insulated transmission line (GIL) was applied, which was initially designed to be insulated with pure SF6. Also to ensure sufficient safety margin for GIL product, the grounded shield ring embedded in the epoxy disc-insulator was used to reduce the electrical field strength in the gas. [ABSTRACT FROM AUTHOR]

In this paper, power frequency breakdown tests as well as positive and negative lightning impulse breakdown tests have been performed. The breakdown voltages of CF3I/CO2/N2, c-C4F8/CO2/N2, CF3I/c-C4F8/CO2 gas mixtures have been measured in different gas pressures, mixing ratios and electrodes distances in slightly non-uniform electric fields. In addition, the breakdown voltages of CF3I/c-C4F8/CO2 gas mixtures have been comparatively analyzed with SF6/CO2, CF3I/CO2, c-C4F8/CO2 gas mixtures. The results show that CO2 is excellent buffer gas to CF3I and c-C4F8 as it has synergistic effect. The power frequency breakdown voltages of CF3I/c-C4F8/CO2 gas mixtures are basically the same as that of c-C4F8/CO2 gas mixtures, which are higher than that of CF3I/CO2 gas mixtures. Besides, the 50% breakdown voltage of c- C4F8/CF3I/CO2 gas mixtures under lightning impulse are higher than that of CF3I/CO2. Compared with SF6/CO2 gas mixtures, CF3I/c-C4F8/CO2 gas mixtures have the same insulating performance in short electrode distance, and show more excellent insulating ability at an electrode distance more than 20mm. [ABSTRACT FROM AUTHOR]

SF6 gas is widely used in power systems, however, it has a strong greenhouse effect. The search for a new environmentally friendly alternative gas has become an urgent task for the power industry. In this paper, CF3I/CO2 gas mixtures in the ratio of 3:7 was tested based on a lightning impulse experimental platform. The 50% impulse breakdown voltage of CF3I/CO2 gas mixtures was determined under various pressures (0.1~0.3MPa) and gaps (5~30mm) and compared to pure SF6 gas. The results indicate that CF3I/CO2 gas mixtures has good insulation properties, reaching 0.84 times that of SF6 gas under slightly non-uniform electric field and 0.65 times that of SF6 gas in extremely inhomogeneous electric field. The polar effect of CF3I/CO2 gas mixtures was also analyzed and the coefficient K is proposed to describe and compare the differences of 50% breakdown voltages under different electric field. The results show that the polar effect of CF3I/CO2 gas mixtures under extremely inhomogeneous electric field is more obvious than that under slightly non-uniform electric field, and the polar reversal phenomenon occurs only under extremely inhomogeneous electric field. Considering various factors, CF3I/CO2 mixtures has the capability of replacing SF6 gas in power equipment such as GIL. [ABSTRACT FROM AUTHOR]

Recent studies suggest that fluoronitriles compound Novec 4710 possesses a dielectric strength two times higher than that of SF6, while with a low global warming potential of only 2400. Mixed with CO2 buffer gas, the Novec 4710 mixtures offer excellent dielectric properties and the possibility to be used as an eco-friendly alternative to SF6 for medium voltage switchgears. This paper focuses on the comparative study of the breakdown strength and partial discharge (PD) characteristics between the fluoronitrile/CO2 mixtures and SF6 under AC voltages. Breakdown tests are conducted under different electrode configurations, i.e., planeplane, sphere-plane, rod-plane, and needle-plane, at different pressures and electrode gaps. In the uniform field, equivalent dielectric strength to SF6 at 100 kPa can be reached by a mixture containing 15% fluoronitrile at identical total pressure; while in non-uniform and highly non-uniform fields, SF6 exhibits higher dielectric strength than 20% mixture. The PD analysis suggests that SF6 has much more PDs with lower magnitude and the 20% fluoronitrile/CO2 mixture has less PDs but with higher magnitude. Due to the different PD characteristics, the corona stabilization effect may be responsible for the higher breakdown strength of SF6 under highly non-uniform field. [ABSTRACT FROM AUTHOR]

The partial discharge (PD) is one of the most common phenomena in power system and it is known that the discharges in the air can produce by-products such as Ozone and NOx gases. Analyzing air decomposition gases can be a potential method in PD detection. To monitoring PD and recognizing PD types by analysis air decomposition products the decomposition characteristics of air under four different kinds of PD needed to be investigated. In this paper a test cell and four kinds of artificial defects have been designed to simulate the air decomposition phenomenon under PD in electrical apparatus. A gases measurement system was established to detect the decomposition gases: O3 and NOx. Experiments of four types of PD simulated by artificial defects with several applied voltages were carried out and the PD and by-products gases were measured simultaneously using pulse current method and Ultraviolet (UV) absorption method. The temperature and pressure were kept constant during testing. The results show that the decomposition characteristics of air under four kinds of PD fault were different in terms of gases concentrations, generation rate and concentration ratios which leads to an indirect way for monitoring and recognizing partial discharge by measuring and analyzing incremental air decomposition by-products. [ABSTRACT FROM AUTHOR]

This paper discusses the validity of applied theoretical methods by which ionization coefficients were derived, assuming the Maxwellian shape of the free-electron gas spectrum in the electronegative SF6 and noble gas mixtures. It has been shown that dc breakdown voltage values calculated in such way are in a good agreement with correspondingly obtained experimental results. The predicted model has been explained by the fact that electronegative gas affects more the low-energy part of free-electron gas spectrum than the high-energy part. Since high-energy electrons have higher probability to initiate the breakdown the Paschen curve obtained under assumption of Maxwellian shape of free-electron gas spectrum does not change significantly. In addition to these observed microscopic characteristics, the influence of the gas insulation recovery time on the macroscopic characteristics was determined by adding the SF6 gas to noble gases. [ABSTRACT FROM PUBLISHER]

Dissolved gas analysis (DGA) is widely used in diagnosing the incipient faults of power transformer. The detector is the key component for this method. Despite various sensors for DGA application, many of them suffer from poor stability and low sensitivity. A solid oxide fuel cell (SOFC) detector is designed in this paper to address these problems. The mechanism of the detector is briefly introduced, and it is fabricated in a mold. The test process is elucidated. For calibration purpose, two mathematical models of the detector, i.e., double-logarithmic model (DLM) and linearity model (LM), are compared with each other. Experimental results demonstrate that the SOFC detector exhibits good repeatability at given concentrations and excellent linearity with DLM. The results indicate that accurate and high-precision measurement of H2, CH4, CO, C2H4, C2H6, and C2H2 can be achieved using the SOFC detector and the proposed DLM. [ABSTRACT FROM PUBLISHER]

Dissolved gas analysis (DGA) remains one of the best non-intrusive methods of assessing transformer health and internal faults. However, few approaches identify consistently the incipient faults initiated by low energy degradation processes. The Low Energy Degradation Triangle (LEDT) method formulates three low energy dissolved gases hydrogen (H2), methane (CH4) and carbon monoxide (CO) into a triangular representation to identify early state changes from normal to unhealthy. The approach has been applied to records of DGA from over 200 generator step-up transformers, to large transmission transformers and industrial units. A degradation parameter derived from the LEDT gave early prediction of the failure of more than 90% of transformers that failed or were removed from service. The approach appears to have benefits for transformer health assessment. It also illustrates an association in some transformers between degradation and geomagnetic disturbances. Additionally, the LEDT indicates there is little benefit from oil treatment after low energy degradation has commenced. [ABSTRACT FROM AUTHOR]

CO2 attracts a lot of attention of researchers as a possible substitute for SF6. The arc interruption capabilities of SF6-CO2 mixtures for different mixed ratios are investigated in this paper by carrying out tests with a 126 kV puffer gas circuit breaker prototype and calculations. Based on the measured arc voltage and current around current zero, the post-arc current characteristics and the thermal interruption properties are investigated for SF6-CO2 mixtures under different rise rate of the recovery voltage RRRV and di/dt before current zero. It is found that the interruption performance of SF6-CO2 increases greatly with increasing SF6 concentration, and the critical RRRV and di/dt before current zero of SF6-CO2 mixtures for SF6 content of 0, 20 and 50% are about 39, 45 and 70% of that of SF6 respectively, at the short-circuit current of 10 kA. The pressure increment at current zero is found to have a great effect on the interruption of the short-circuit current. In addition, the pressure buildup in CO2 is much lower than that in SF6 for both no-load and loaded operations. [ABSTRACT FROM AUTHOR]

CF3I and mixed gases containing CF3I are potential substitutes of SF6 in electrical equipment. In this paper, we studied the feasibility of replacing SF6 with CF3I/N2 in terms of power frequency breakdown performance under the influence of gas pressure, mixing ratio, and electric field. The synergistic effect, liquefaction temperature, and self-recover ability of CF3I/N2 were analyzed. Experimental results showed that, under a highly uniform electric field, the sensitivity of the power frequency breakdown characteristics of the gases to pressure shows the order SF6CF3IN2. The power frequency AC breakdown strength of CF3I/N2 (30%/70%) at electrode distances of 5 and 10 mm could reach over 0.9 and 0.85 times that of SF6 at 0.3 MPa, respectively. CF3I/N2 showed positive synergistic effects and the improvement was attributed to N2. CF3I presents excellent self-recoverability. The optimum ratio of CF3I/N2 to replace SF6 gas as insulating medium is 30% at 0.3 MPa. [ABSTRACT FROM AUTHOR]

A new method was introduced to evaluate and analyze synergistic effect including negative synergistic effect of SF₆/N₂ gas mixtures breakdown voltage. This method provides an intuitional comparison among different degree of synergistic effect through a simple equation of the normalization coefficient h. The disadvantages of traditional method, which fails to evaluate negative synergistic effect and would be inaccurate when breakdown voltages of the two gas compositions are close, are overcome via the method. In this paper, a typical example of the above is shown to analyze synergistic effect and abnormal negative synergistic effect of SF₆/N₂ gas mixtures in non-uniform electric field under lightning impulse. Meanwhile the validity of the normalization coefficient h with the synergistic effect of SF₆/N₂ gas mixtures under various voltage conditions and electrodes in references was verified. [ABSTRACT FROM PUBLISHER]

Several methods have been proposed for dissolved gas analysis (DGA) of mineral oil in power transformers. One of the simple and most widely used methods is Duval triangle. However, Duval triangle does not consider the concentrations of two combustible gases, namely ethane (C2H6) and hydrogen (H2). As a result, Duval triangle exhibits a lower accuracy in diagnosing certain fault types, for which these gases are the key gases, such as low overheating and corona discharge. Accordingly, this paper proposes a novel graphical technique for DGA based on all the five combustible gases. The proposed graphical technique is developed in the form of a pentagon shape. The pentagon heads represents the percentage concentration of each individual gas to the total combustible gases. The corresponding point for a certain faulty case is determined by the center of mass of all pentagon heads. The knowledge extracted from previous DGA methods and field experiences are used to estimate the preliminary fault regions within the pentagon. The exact boundaries between fault regions are then specified using actual DGA data with corresponding fault types collected from the Egyptian Electricity Network and published cases. The overall performance of the proposed pentagon has been evaluated using a set of fault cases and it is revealed that the proposed pentagon has higher diagnostic accuracy compared to other methods including Duval triangles and IEC standard 60599. [ABSTRACT FROM AUTHOR]

In this paper a prediction model is proposed for estimation of furan content in transformer oil using oil quality parameters and dissolved gases as inputs. Multi-layer perceptron feed forward neural networks were used to model the relationships between various transformer oil parameters and furan content. Seven transformer oil parameters, which are breakdown voltage, water content, acidity, total combustible hydrocarbon gases and hydrogen, total combustible gases, carbon monoxide and carbon dioxide concentrations, are proposed to be predictors of furan content in transformer oil. The predictors were chosen based on the physical nature of oil/paper insulation degradation under transformer operating conditions. Moreover, stepwise regression was used to further tune the prediction model by selecting the most significant predictors. The proposed model has been tested on in-service power transformers and prediction accuracy of 90% for furan content in transformer oil has been achieved. [ABSTRACT FROM AUTHOR]

Thanks to its excellent insulation and cutoff performances, SF6 gas has been applied to power equipment since the 1960s and is now widely used for several kV to 1,000 kV-class GIS, GCB, and GIL. However, since 1997, when SF6 was designated at COP3 as a greenhouse gas to be reduced, there has been a wish to use an alternative insulating gas to pure SF6 gas. In the present study, alternative gases were selected from among mixtures excluding SF6 with the need to reduce GWP (global warming potential) in mind. Gas mixtures containing such substances and with a boiling point of -20°C or less, chemically stable, non-toxic, and not ozone-depleting were prioritized. Furthermore, the availability and environmental performance were taken into consideration when deciding on component gases. Consequently, to launch this series of studies, four types of gas mixtures were used combining a gas in Group A (C2F6, C3F8) ? electronegative gases with relatively high dielectric strength ? and a gas in Group B (N2, CO2) ? gases existing in the natural world. The GWP of SF6 is 22,800 whereas that of C2F6 is 12,200 and that of C3F8 is 8,830, or several times smaller than that of SF6. In the present paper, insulation characteristics were experimentally obtained while varying the mixture ratio under a quasi-uniform electric field assuming GIS. Consequently, compared to the GWP of pure SF6, the GWP was about 12% to 38% for gas mixtures with C3F8/N2 or C3F8/CO2 and 18% to 70% for gas mixtures with C2F6/N2 or C2F6/CO2. Consequently, it emerged that, while assuming breakdown voltage proportional to gas pressure, the GWP was likely to be reduced by 30% to 90% while maintaining dielectric strength. In addition, a study was conducted on the synergism of a gas mixture through analysis using the Boltzmann equation. Consequently, the synergism was confirmed while its degree varied depending on the type of each gas mixture, and the mechanism thereof was clarified. [ABSTRACT FROM PUBLISHER]

The application of non-thermal plasma excited by strong electric fields is becoming a key technology for water treatment because of the efficient generation of oxidants, such as hydroxyl radicals, and no secondary pollution. In this paper, a water treatment system mainly consisting of a pulsed power generator and a dielectric barrier discharge reactor was constructed. The reactor consists of five rows of staggered positive and negative electrodes and separating plates. Wastewater dropped into the discharge area from the tiny holes in the separating plates. Degradation of indigo carmine solution was attempted by this system. The effects of discharge time, discharge voltage, frequency, initial pH value, and H2O2 were studied. The degradation rate came to 100% in 8 minutes at the voltage of 30 kV and frequency of 200 Hz under the initial concentration of 450 mg/L. The energy cost of the degradation of indigo carmine reached 80 g/kWh. [ABSTRACT FROM PUBLISHER]

This paper presents a comparative study on SF6 alternative candidate gases for the surface insulation performance of eco-friendly Gas Insulated Switchers (GIS) and Solid Insulated Switchers (SIS). The candidate gases including N2/O2 mixture gas, dry air, and compressed air were proposed based on AC surface flashover experiment. These gases were compared and examined based on their surface insulation performance, pressure and gap dependence, surface insulation reliability in different temperatures, economic feasibility and easiness of manufacture. The comparison results verified that dry air had excellent properties on the comparison criteria and was the most suitable eco gas among the candidate gases for eco-friendly GIS and SIS. In addition to the comparative study on the candidate gases, their surface flashover characteristics were described in detail based on the effect of moisture contained in the candidate gases on flashover voltage and the correlation among electric field intensity, collision-ionization coefficient, electron attachment coefficient, and gap length. [ABSTRACT FROM AUTHOR]

The dissolved gas analysis (DGA) is a well-accepted power transformer predictive maintenance technique. However, despite the importance of the technique, classical diagnostic methods were developed from observations of simplified thermodynamic and compositional models. This paper presents the development of a DGA diagnostic method based on a thermodynamic model that includes a contribution inspired on the kinetics of the process. The performances of the new phenomenological proposition and of classical DGA diagnostic methods are compared and discussed. Also, a general procedure for the application of the new diagnostic method is described. [ABSTRACT FROM AUTHOR]

The objective of this paper is to propose mechanisms of gas desorption induced discharge and their polarity effect. Three electrode pair types were combined in the in-situ experimental apparatus with high vacuum; air-exposed cathode and anode, airexposed cathode and conditioned anode, conditioned cathode and air-exposed anode. Electrode pairs were subjected to repetitive impulse voltage breakdowns till conditioning saturation. The results showed two gas desorption induced discharge mechanisms; namely, pulsed current discharge (PCD) and pulsed current induced breakdown (PB). Many gas desorption induced discharge (PCD and PB) occurred in air-exposed cathode and anode pair and air-exposed cathode and conditioned anode pairs. While only a few discharges occurred in the conditioned cathode and air-exposed anode pair. The gas desorption induced discharge in vacuum showed a polarity effect; Only when the cathode electrode of the pair was the original air-exposed electrode, no matter the anode electrode was or not, gas desorption induced discharge (PCD and PB) could occur in the beginning stage of the conditioning. The physical evolution of gas desorption induced discharge is explained. [ABSTRACT FROM AUTHOR]

Recent studies have demonstrated that fluoronitrile (FN) Novec™ 4710 and fluoroketone (FK) Novec™ 5110 show higher dielectric strength than SF 6. These gases can be mixed with a buffer gas such as CO 2 and technical air to have suitable dielectric properties for high voltage insulation applications. With the rapid growth of HVDC networks, these gases may replace SF 6 in future HVDC apparatus such as GIS/GIL. This paper focuses on the study of the partial discharge (PD) characteristics of SF 6 and SF6 alternative gases with a protrusion defect on the high voltage conductor with DC voltage. The results show that, for calculated equivalent SF 6 dielectric strength under homogeneous electric field, a difference in terms of partial discharge inception voltage was noted for gas mixtures compared to SF 6. This difference may be due to the influence of gas pressure under highly inhomogeneous electric field. FN-CO 2 and FK-Air mixtures showed the highest PD amplitude under positive polarity while it was higher under negative polarity for SF 6. Moreover, PD repetition frequency is higher for SF 6 investigated alternative gases. The results can help for the design of SF 6 free HVDC GIS partial discharge monitoring system. [ABSTRACT FROM AUTHOR]

Recently, water treatment using pulsed streamer discharge in water is studied, because the pulsed streamer discharge generates active species that decompose organic compounds in water. We have studied the method spraying water droplets into discharge space as one of the water treatment methods. In this paper, improvement of a treatment rate by changing structure of reactor has been investigated. At first, the influence by changing an electrode and packing pellets was investigated. The indigo carmine solution was decomposed as sample water. As the result, the treatment efficiency for the discharge energy was decreased by using the reactor of longer electrode and using the reactor with the pellets. The reason of the decrease of the treatment efficiency is that water droplets become water film and that the voltage falls due to the increase of capacitance components of the electrode. To solve these problems, the reactor setting the insulation grids was investigated. This reactor improved the treatment efficiency because setting the insulation grids prevented the fall of energy efficiency by the long electrode and quickened the decomposition of the organic compounds. [ABSTRACT FROM PUBLISHER]

Currently, environmental problems such as global warming are important issues, and SF6 has been identified as a greenhouse gas with a long atmospheric lifetime. Therefore, in the long term, it is preferable to reduce the amount of SF6 used as an insulating gas. It is thus important to discuss the possibility of using more environmentally friendly gases as alternative insulation for gas-insulated apparatus. In this paper, we describe the fundamental insulation breakdown characteristics of high-pressure CO2 gas at gas pressures of up to 1.0 MPa under simulated practical conditions, including the insulation breakdown characteristics of a high-voltage conductor with an insulating coating and the effect of decomposition products on the creeping insulation of a spacer. With the aim of enhancing insulation performance, we discuss the effect of the type of insulating coating on insulation performance. The breakdown electric field was increased by 20% by coating the conductor. It was verified that the application of an insulating coating is a practical method for enhancing the insulation performance of high-pressure CO2 gas. It was also verified that the decomposition products have only a slight effect on the creeping insulation of the spacer except for when there is heavy pollution on the insulating spacer. However, if a large amount of decomposition products is expected to be deposited on the insulating spacer during operation, which may cause a severe interruption to the current, it will be necessary to consider this factor in the insulation design. [ABSTRACT FROM AUTHOR]

This paper describes discharge properties of N2 and CO2-based gas mixtures including a perfluorocarbon (PFC) gas such as CF4, C3F8 and c-C4F8 under non-uniform field. The mixture ratio between a base gas of N2 or CO2 and the additive PFC gas was fixed as 9:1; namely, 90%N2/10%PFC or 90%CO2/10%PFC gas mixture. The PFC gases have even smaller global warming potential (GWP) than SF6 gas and have good insulation properties as SF6 gas. Thus, PFC gas mixture is expected to be a SF6 substitute without highly pressurizing the gas over the conventional pressure of 0.5 to 0.6 MPa. in this study, in order to compare the partial discharge (PD) inception voltage VPD and breakdown voltage VB properties between N2 and CO2-based gas mixtures, as well as between the additive gas of PFC and SF6 gas, we investigated these properties of the gas mixtures with a needle to plane electrode under ac high voltage application. The gas pressure was changed from 0.1 to 0.6 MPa. As a result, it was found that VPD and VB characteristics of N2 and CO2-based gas mixtures differed considerably, especially the gas pressure dependence of VB (so-called the N shape characteristics). VB characteristics of N2-based gas mixture including c-C4F8 proved to be excellent within the test conditions over the wide gas pressure region, showing the maximum breakdown voltage. In terms of VPD properties, CO2-based gas mixture had an advantage over N2-based gas mixture due to higher VPD.Furthermore, we discussed the synergy effects of VPD and VB for N2 and CO2-based gas mixtures using the index Rn which was defined to quantify the degree of the effect. Rn for CO2-based gas mixture was higher than that of N2-based gas mixture. [ABSTRACT FROM AUTHOR]

Dissolved gas analysis (DGA) of transformer oil is one of the most effective power transformer condition monitoring tools. There are many interpretation techniques for DGA results. However, all of these techniques rely on personnel experience more than standard mathematical formulation and significant number of DGA results fall outside the proposed codes of the current methods and cannot be diagnosed by these methods. To overcome these limitations, this paper introduces a novel approach using Gene Expression Programming (GEP) to help in standardizing DGA interpretation techniques, identify transformer critical ranking based on DGA results and propose a proper maintenance action. DGA has been performed on 338 oil samples that have been collected from different transformers of different rating and different life span. Traditional DGA interpretation techniques are used in analyzing the results to measure its consistency. These data are then used to develop the new GEP model. Results show that all current traditional techniques do not necessarily lead to the same conclusion for the same oil sample. The new approach using GEP is easy to implement and it does not call for any expert personnel to interpret the DGA results and to provide a proper asset management decision on the transformer based on DGA analysis. [ABSTRACT FROM PUBLISHER]

Understanding how a gas is able to strongly insulate electric devices is certainly of great importance to the electrical engineering community. More precisely, modeling how a dielectric gas stops an electric current requires to understand what makes a gas a good dielectric, or in other words, what makes a gas presenting a high dielectric strength (DS). In this paper, we show how to easily estimate the DS of a gas by calculating its ability to absorb light. [ABSTRACT FROM AUTHOR]

The paper reports a new transversal study of dielectric coating effects on high voltage (HV) electrodes in SF6 and eco-friendly gases like CO2, dry air and N2 for real-size gas insulated switchgear (GIS). From a practical viewpoint, the breakdown electric field (BDE) data of the following test conditions are collected; 1) large effective electrode area over about 5 x 104 mm2, 2) actual GIS cylindrical configuration of utilization factor of around 0.6, 3) high gas pressures up to 1.9 MPa for actual GIS. The BDEs of dielectric coated electrodes relative to those of bare electrodes (normalized BDEs) are systematically evaluated as a function of dielectric coating thickness and gas pressure. As a result, the normalized BDEs in percentage terms are 105-150% (average value of around 110%), which does not depend on the gases. Remarkable performances of the normalized BDEs of 120-150%, which correspond to nearly 90% of the theoretical BDEs of the gases, are observed in SF6 and CO2 for "thick casting epoxy coating", "thin coating of comparable dielectric performance to casting epoxy" and "hard anodic-oxide coating & PTFE-immersion" that have fewer defects inside. The normalized BDEs in N2, however, show poorer dielectric performances than the other gases especially in the high pressure region above 1.0 MPa. The dielectric coating effects are more pronounced as increasing the thickness for all the gases. The pressure dependences of the dielectric coating effects are not clearly recognized for all the gases and all the coating conditions except for the "thick casting epoxy coating". The coating effect in N2 decreases slightly as raising gas pressure. The application examples and application limits of the dielectric coatings to GIS are also presented. These new cross-sectional studies of dielectric coated electrodes are an effective approach to get new findings to realize a future eco-friendly compact GIS. [ABSTRACT FROM PUBLISHER]

Partial discharge (PD) is usually aroused before the failure of gas insulated switchgear (GIS) caused by defects, which results in the decomposition of the SF6 used as insulating gas. Analyzing SF6 decomposition products can aid in PD detection. Before recognizing PD types by analyzing SF6 decomposition products, the decomposition characteristics of SF6 under different types of PD should be investigated first. In this paper, a gas chamber and four typical types of artificial defects were designed to simulate the SF6 decomposition phenomenon under PD in GIS. A gas chromatography system was established to detect SF6 decomposition products. By selecting the chromatographic column, SF6 decomposition products were successfully separated and their concentrations were measured. Numerous SF6 decomposition experiments under four kinds of PD generated by four kinds of artificial defects were carried out and the SF6 decomposition products produced by each experiment were detected. The decomposition characteristics of SF6 under the four defects were different in terms of decomposition amount, generation rate, and concentration ratio, among others. It is feasible to recognize the type of PD by analyzing SF6 decomposition products. [ABSTRACT FROM AUTHOR]

Research efforts at Texas Tech University on impulse antenna phased array has resulted in the development of a dependable high voltage, high repetition rate switch that can minimize jitter into the ps range. To accurately synchronize a phased array to steer and preserve the risetime of a radiated pulse, the jitter can only be a fraction of this risetime. Initial testing with a similar system in [1] produced sub-ns jitter results for operations in different gases and gas mixtures. This paper discusses in detail 50 kV, 100 Hz switch operations using different testing parameters. The switch jitter as a function of triggering conditions is discussed, including a comprehensive evaluation of jitter as a function of operation pressure as well as trigger magnitude. Several phenomenon were observed and discussed to quantify the switch jitter with respect to operation pressure and trigger magnitude. The temperature of gas and its effects on switch jitter is also documented in this paper, with a jitter improvement of ~25% recorded. An empirical formula was determined as a function of the gas density, electric field of the main gap, and electric field for the trigger for the experiments conducted in this manuscript. A 50 Ω, 1 nF pulse forming line is charged to 50 kV and provides the low inductance voltage source to test the switch. The hermetically sealed spark gap, with a modular design composed of copper tungsten electrodes, gas feeds, Kel-F lining, as a well as a G-10 shell is used to house the high pressure gases for the experiments. Trigatron-type triggering is provided by a solid state opening switch voltage source that supplies 75-150 kV, 10 ns risetime pulses at a rep rate up to 100 Hz in burst mode. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the electrical strength of gases exposed to the influence of partial discharges. Experimental methods and procedure; Measurement results; Discussion.

We report on research into methods to improve the lifetime of insulators in multi-stage gas switches exposed to microsecond kV pulses at 20 Hz repetition rate. Two sets of experiments are reported; first on a comparison of polyetheretherketone (PEEK) and polyimide (PI) insulation. The results shows that the lifetime of PI far exceeds that of PEEK, which is attributed to the softening temperature of PI being higher than that of PEEK. In the second experiment, two methods are used to enhance the lifetime of PI; the first is to gild the surface of PI insulators, and the second is to insert PI films between the insulators and the electrodes. Both methods significantly increase the PI lifetime, but the film method leads to a longer lifetime than the gilding method. Imaging the insulator surfaces at the microscopic level reveals that local regions are not smooth, which results in greater electron emission from the cathode. The gilding method lowers electron emission and ejection and the film method blocks electron emission and ejection and thus they enhance the lifetime of PI insulators in multi-stage gas switches. [ABSTRACT FROM AUTHOR]

This paper discusses the efficiency of a moderation effect in a mixture of SF6 and N2 gases, in case of the application of impulse voltages with varying rise times. The moderation in question pertains to the slowing down of free electrons through nonelastic collisions with molecules of N2 gas, which increases the probability, i.e. the effective cross-section, for the formation of negative ions of SF6 . Variable parameters included relative mixture composition, pressure, inter-electrode gap, shape of the electric field, and the manner of electrode surface processing. By applying statistical analysis to experimentally obtained values of the impulse breakdown voltage random variable, and presenting the results as impulse characteristics, it was established that a positive synergetic effect of adding N2 gas into the mixture was achieved at smaller impulse speeds. This effect was lost at greater impulse speeds. The obtained results were explained by examining the relative ratio of the time constant characterizing the process of moderating the spectrum (statistical distribution of energy) of free electrons, to the characteristic time of elementary electric discharge processes in gases. [ABSTRACT FROM AUTHOR]

This paper deals with the characterization of discharges initiated in mineral oil and the gases that they generate depending on their energy levels. Different types of discharges are identified in function of the electrode geometry and the applied voltage. Each type of discharge is analysed through the generating gases and the processes implicated in oil degradation are discussed according to different standard specifications. By estimating the forms of energy that can be involved in the gas formation, it was evidenced that vaporisation processes are as important for discharges of weak energy as for those of high energy. [ABSTRACT FROM AUTHOR]