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This study is devoted to the improvement of the transformer oil quality, using a new inhibiting additive, since the extensively used inhibitory additive ionol is sensitive to organosulfur compounds of sulfur oils. From the earlier works, the organosulfur compounds are known to affect ambiguously the transformer oils characteristics. Therefore, it was of interest to study the individual sulfides as the inhibitory additives. The goal was achieved by the researches with the use of the model mixtures consisting of the selectively purified transformer oil (free from ionol) along with the individual sulfides, decylcyclohexylsulfide and decylfenylsulfide, at concentration of 0.5 %, Their effect on stability against oxidation of the selectively purified oil, on its electric strength and tangent of the dielectric losses’ angle was studied. The primary results obtained were, firstly, the rate slowing down of water formation in oil and of water-soluble acids formation in oil upon its oxidation in the presence of the individual sulfides, and, secondly, an increase in the electric strength and decrease in the dielectric losses compared to the transformer oil, containing ionol. It was established that decylcyclohexylsulfide inhibitory properties are stronger compared to those of decylfenylsulfide, which was testified by less quantities (by 1.8 times) of the water formed and of water-soluble acids (by 2.22 times). The introduction to oil of 0.5 % decylcyclohexylsulfide and decylfenylsulfide increased the oil electric strength, correspondingly, by 2.6 and by 5.5 times, upon water concentration in oil equal to 15·10-2 g/kg. The significance of the results obtained is in improving the transformer oil quality produced from the sulfur oils with the use of a novel additive.

Electrical industry uses oils for cooling and insulation of several machines, such as power transformers. In addition, it uses water for cooling some synchronous generators. To avoid malfunctions in these assets, fluid quality should be preserved. To contribute to this aim, a sensor that detects changes in fluid composition is presented. The designed sensor is like a single-phase transformer whose magnetic core is the fluid whose properties will be measured. The response of this device to a frequency sweep is recorded. Through a comparison between any measurement and a reference one corresponding to a healthy state, pollutants presence, such as water in oil or salt in water, can be measured. The performance of the sensor was analyzed through simulation. In addition, a prototype was built and tested measuring water concentration in oil and salt content in water. The correlation between pollutant concentration measured with the sensor and known pollutant concentrations is good.

Power transformers are considered to be the most important assets in power substations. Thus, their maintenance is important to ensure the reliability of the power transmission and distribution system. One of the most commonly used methods for managing the maintenance and establishing the health status of power transformers is dissolved gas analysis (DGA). The presence of acetylene in the DGA results may indicate arcing or high-temperature thermal faults in the transformer. In old transformers with an on-load tap-changer (OLTC), oil or gases can be filtered from the OLTC compartment to the transformer&rsquo, s main tank. This paper presents a method for determining the transformer oil contamination from the OLTC gases in a group of power transformers for a distribution system operator (DSO) based on the application of the guides and the knowledge of experts. As a result, twenty-six out of the 175 transformers studied are defined as contaminated from the OLTC gases. In addition, this paper presents a methodology based on machine learning techniques that allows the system to determine the transformer oil contamination from the DGA results. The trained model achieves an accuracy of 99.76% in identifying oil contamination.

Reliable operation of a power transformer with a certain load depends on the technical condition of individual construction parts and the ability to prevent defects that can cause a failure. During the lifecycle of a transformer, valuable data is constantly accumulated, which forms the basis for technical or risk assessment of the equipment. Therefore it also serves as a ground for the decisions on further operation, or repairs, or replacement. To achieve this goal, data need to be systematized. Since technical condition indexing allows combining various types of data including results of diagnostic tests is used within the framework of this research. As part of a larger risk assessment methodology, algorithms for two indicators are proposed in this paper, and they are based on results of electrical measurements and analysis of oil parameters, respectively. The novelty of the algorithms for indicators introduced in this paper is based on analysis of features specific to the power system in Latvia such as large proportion of aged transformers, low loading level, significant variation in oil volumes, and statistics on typical faults. Proposed limits of parameters are verified with data from operation history. Taking into account the differences in the measurement periodicity, the indicator that is based on electrical measurements assesses the individual constructive parts of the transformer (windings and core, bushing and on-load tap changer) separately, whereas the other, indicator combines the results of oil parameters into a single assessment. These indicators were verified by using 30 transformers from the Latvian power system and the obtained results coincide well with the operation history.

International audience; The condition of the solid insulation paper within transformers can be directly determined from the degree of polymerization (DP) measured from samples. Since this is difficult for in service units, many studies have been performed in regard with indirectly measuring the degradation of paper insulation by chemical markers for several decades. The 2-FAL concentration is being used decades ago. In this contribution, condition monitoring history and experience with transformer fleets are reported for a service aging of 75 years. 37 oil-filled transformers (146.7 kV to 157 kV) of a Canadian utility were periodically monitored. As part of the maintenance of the apparatus, the analysis of the furanic compounds is carried out. These are obtained by high performance liquid chromatography in a laboratory, with a regularity that varies according to the age of the transformer. This article deals with a transformer aging evaluation tool built from fuzzy logic. A fuzzy inference system is implemented by taking as input the values of 2-FAL and CO 2 /CO ratio. The tool helps directly providing the paper condition.

Predictive maintenance strategies in power transformers aim to assess the risk through the calculation and monitoring of the health index of the power transformers. The parameter most used in predictive maintenance and to calculate the health index of power transformers is the dissolved gas analysis (DGA). The current tendency is the use of online DGA monitoring equipment while continuing to perform analyses in the laboratory. Although the DGA is well known, there is a lack of published experimental data beyond that in the guides. This study used the nearest-rank method for obtaining the typical gas concentration values and the typical rates of gas increase from a transformer population to establish the optimal sampling interval and alarm thresholds of the continuous monitoring devices for each power transformer. The percentiles calculated by the nearest-rank method were within the ranges of the percentiles obtained using the R software, so this simple method was validated for this study. The results obtained show that the calculated concentration limits are within the range of or very close to those proposed in IEEE C57.104-2019 and IEC 60599:2015. The sampling intervals calculated for each transformer were not correct in all cases since the trend of the historical DGA samples modified the severity of the calculated intervals. This work was partially financed by the EU Regional Development Fund (FEDER) and the Spanish Government under RETOS-COLABORACIÓN RTC-2017-6782-3 and by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 864579 (FLEXIGRID).

Power transformers are crucial elements in electrical systems, and the end of their useful life is commonly conditioned by the degradation of the cellulosic insulation materials inside them. These materials are subjected to elevated temperatures and mechanical stresses, generated by electrical solicitations which deform the copper conductors and subsequently the paper, and also to the chemical reactions which take place in the dielectric oil in which the paper is impregnated. In order to better understand the behaviour of cellulosic insulation, we have studied the previous bibliography analysing the mechanical behaviour of cellulosic materials. At present, there are no experimental results analysing how the paper responds to the deformation suffered by the copper conductor in a realistic situation. We have developed a simulation model describing the mechanical behaviour of a standardised copper conductor wrapped with four layers of dielectric paper, using ANSYS Workbench Static Structural, which will be compared with experimental results afterwards.

Insulators or bushings are one of the most common cause of transformer failures especially those with fire and collateral damage. This can be prevented by application of off-line and on-line monitoring, especially by measuring of capacitance C and dielectric dissipation factor tanδ, but current physical understanding of these parameters should be improved. A complex research of temperature dependence of C and tanδ, which is based on measurements on a specially designed oil impregnated paper bushing models with different moisture contents in the insulation and during artificial ageing, is presented in the paper. Useful relationships, which enable calculation of tanδ as a function of observed influencing parameters, are also presented.

The nature and causes of corrosive sulfur induced failures are examined in oil-filled transformers and shunt reactors. Copper sulfide, which is formed when the corrosive sulfur in a mineral oil reacts with the copper conductors, is likely to diffuse into the paper tapes insulating the conductors. Since copper sulfide is partially conducting, the dielectric losses of the contaminated oil-impregnated-paper tapes are markedly increased; paper tapes in close proximity to the copper conductors are found to attain tan delta values > 1.0 even at room temperature. It is highly likely that thermal instabilities develop at those sites at operating temperatures, leading to increased loss currents and, ultimately, short circuits between the turns. This sequence of events is substantiated by evidence from the field, which indicates large areas of thermally degraded insulations and charred breakdown regions along the coils, the extent of which becomes more pronounced at higher operating temperatures (toward the top of the windings).

DC power transmission is gaining considerable importance and converter transformers form an important component in it. An insulation of these transformers is stressed by both ac and dc voltages. Particle contamination is one of the major problems in insulation structures as it generates partial discharges (PD). If a particle is moving between the ground electrode and barrier, the magnitude of partial discharges formed is less compared to that of its movement between two metal electrodes. On the other hand, when the particle is lying over the barrier insulation material, it does not lead to any partial discharge activities as observed under ac/dc voltages. Broadband measurement of UHF signals produced by partial discharges due to particle movement in transformer oil under dc voltages, at high applied electric fields, indicates that the frequency content of the signal lies in the entire UHF range of 300 MHz - 3GHz. Narrow band measurements of UHF signal due to PD formed by particle movement, at 1GHz, indicates that, in the presence of barrier, an increase in applied voltage results in increase in number of partial discharge pulses. This phenomenon occurs in converse in oil gap without any barrier. In the presence of barrier, the sequential movement of particle occurs and the magnitude of discharges increases with increase in applied voltage, irrespective of polarity of the dc voltage. The number of discharges that occur under ac voltage is high compared to the dc voltages. � 2006 IEEE.

The number of (hybrid) electric vehicles is growing, leading to a higher demand for electricity in distribution grids. To investigate the effects of the expected peak demand on distribution grids, a stress test with 15 electric vehicles in a single street is conducted and described in this paper. The test is conducted in a neighbourhood where both transformers and households are equipped with measurement devices. A significant maximum power consumption increase (more than double) is observed at one transformer when both the electric vehicles and domestic loads stress the network. The observed voltage drop in the network is 17V. Analysis further shows that the hosting capacity is around 15%–20% for the investigated networks and that under voltage is unlikely to occur. The measurements are compared to a simulation and the results show that the simulations predict the actual measurement accurately.

International audience; This work is devoted to the modeling of branching streamers propagating in transformer oil using an equivalent electrical network and the electrical network computation. The proposed model enables to determine the different characteristics of the streamer (i.e., the associated current and the electrical charge, the power and the energy injected in the liquid, the local electric field at the streamer head, the streamer shape and its velocity, the mobility of the charge carriers within the streamer channels, the local viscosity and temperature). It's shown through the simulated values of the mobility of charge carriers, the local viscosity and temperature that both electronic and gaseous mechanisms are implicated in the streamer development. The gaseous nature of streamers and the role of the local electric field are evidenced. The influence of the conductivity and additives as well as the electrode gap on the propagation velocity of positive streamers is analyzed.