Insulation Oil Research Articles

Synthesis and characterization of cooling biodegradable nanofluids from non-edible oil for high voltage application

Mineral oil has been serving well as a cooling and insulation oil in high voltage power equipment but with a setback when considering environmental friendliness whenever there is spillage due to its poor carbon profile. Several works have been done on the enhancement of dielectric properties of green alternative with different nanoparticles but little attention was placed on its cooling properties which is one of the major functions of the oil. Also, to prevent food competition, esters from a non-edible seed oil should be given more consideration. This work, therefore, investigates the cooling properties of synthesized insulating nanofluid using Neem oil ester as the base fluid together with (Insulating) SiO2 and (semiconductive) WO3 nanoparticles. The nanoparticles were characterized using FTIR and XRD to confirm their functional groups and crystallite size respectively. Transesterification of the oil was done using sodium methoxide and the nanofluid samples were prepared by dispersing the nanoparticles into the oil. The nanoparticles were varied from 0.2 wt% to 1 wt%. The pour point, flash point and viscosity were measured according to ASTM standards. An increase in the pour point, flash point and viscosity were observed at every loading of the nanoparticle. The nanofluid with dispersed SiO2 nanoparticles were observed to possess superior properties as a cooling liquid in high voltage power equipment when compared with the fluid with WO3 nanoparticles because of its low viscosity, low pour point and good flash point. After the ageing, the synthesized fluids still retained their properties which is better than the mineral oil.

Characterization of Dielectric Oil with a Low-Cost CMOS Imaging Sensor and a New Electric Permittivity Matrix Using the 3D Cell Method.

In this paper, a new method for characterizing the dielectric breakdown voltage of dielectric oils is presented, based on the IEC 60156 international standard. In this standard, the effective value of the dielectric breakdown voltage is obtained, but information is not provided on the distribution of Kelvin forces an instant before the dynamic behavior of the arc begins or the state of the gases that are produced an instant after the moment of appearance of the electric arc in the oil. In this paper, the behavior of the oil before and after the appearance of the electric arc is characterized by combining a low-cost CMOS imaging sensor and a new matrix of electrical permittivity associated with the dielectric oil, using the 3D cell method. In this way, we also predict the electric field before and after the electric rupture. The error compared to the finite element method is less than 0.36%. In addition, a new method is proposed to measure the kinematic viscosity of dielectric oils. Using a low-cost imaging sensor, the distribution of bubbles is measured, together with their diameters and their rates of ascent after the electric arc occurs. This method is verified using ASTM standards and data provided by the oil manufacturer. The results of these tests can be used to prevent incipient failures and evaluate preventive maintenance processes such as transformer oil replacement or recovery.

Electrical Breakdown Voltage of Palm Oil and Nano Graphene Filler in Nanofluids Application on Transformer Insulating Oil

Generally, power transformers have been using mineral oil as a liquid insulator due to its availability and excellent dielectric property. However, petroleum sources are depleting, which implies that mineral oil is going to be limited in availability. So, this research is to investigate on vegetable oil with nanographene filler as a substitution. Vegetable insulating oil is considered as environment-friendly insulating oil due to their superiority of biodegradable, nature-friendly, high fire-point, and good level of breakdown voltage (BV). Nevertheless, vegetable insulating oil have high viscosity, leading to a slow flow rate on the cooling performance of power transformers. To solve this problem, a process of transesterification was used to produce palm oil methyl ester (POME) from a refined bleached deodorized palm olein (RBDPO) to reduce its viscosity. RBDPO and POME were used as two kinds of fluid-based to combine with graphene nanoparticles (GNPs). Electrical breakdown voltage tests were performed by the IEC60156 standard. The results shown that POME have higher BV than RBDPO but adding GNPs may lead to lower BV even with a small amount of concentration. Nevertheless, every nanofluid has a higher BV than 30 kV.

Pengujian Sifat Fisika dan Listrik Minyak Kelapa Sebagai Alternatif Isolasi Pada Trafo Daya

Transformer oil insulation material is the result of processes from petroleum, the material that is not able to be renewed, increasingly scarce, expensive, an imported commodity, and the need is increasing. So it is necessary to strive for alternative transformer oil that comes from renewable materials, based on domestic production, increases the added value of a commodity and environmentally friendly. The alternative transformer oil in this case is coconut oil. For this reason, it is necessary to test the feasibility of coconut oil as an alternative to transformer oil which includes testing of physical, chemical and electrical properties. The test results are compared with the standard transformer oil according to the IEC. The test results, the flashpoint and dielectric strength are feasible as an alternative to transformer oil, the density, volume expansion coefficient and viscosity of coconut oil are not suitable for use as an alternative to power transformer insulation oil. The percentage in terms of physical properties is 25%, with 4 tests of 10 existing physical properties. The feasibility of electrical properties is 50% with 1 test of 2 existing electrical properties.

A review: Research on corrosive sulphur in electrical power equipment

Corrosive sulphur has been commonly regarded as an enormous threat to electrical power equipment in recent decades. Cuprous sulphide (Cu2S) deposition on the insulating oil and paper insulation caused by sulphur corrosion will bring about insulation deteriorations or failures in power transformers and shunt reactors. A large number of experiments have been carried out to investigate sulphur corrosion and some measures have been come up to solve this issue such as replacement of insulating oil, chemical removal of corrosive sulphur and the addition of passivator and so on. However, there has not been a perfect method to work out this problem completely, and the phenomenon of sulphur corrosion still occurs. This paper intends to provide thorough information of corrosive sulphur in power equipment and give detailed explanations about its corrosion mechanism, hazards and control measures, which is supposed to offer a reference for subsequent researchers.

ASSESSMENT OF THE ELECTRICAL EQUIPMENT INSULATION STATE USING THE GRADIENT BOOSTING ALGORITHM

The creation of analytical software products aimed at assessing the electrical equipment state has become a priority in the development of diagnostics in the power industry. The artificial intelligence methods are useful for this problem-solving. In the article, we propose a method for analyzing the monitoring data of partial discharges in the insulation of electrical equipment using machine-learning technologies. An analytical assessment of the partial discharges characteristics allows us to conclude on the insulation state of the object. It is proposed to use integrated diagnostic parameters, such as partial discharges intensity – the maximum measured value of the apparent charge of a single, repetitive and regular partial discharges. The total sample is characterized by an imbalance, which is typical for technical diagnostics in general. Among machine learning algorithms, bagging and boosting have proven to be the most effective. The mathematical apparatus of gradient boosting is considered in the example of the most common algorithms GBM (Gradient Boosting Machine) and CatBoost. The model was created in the Python programming language. The model created on the basis of the CatBoost algorithm was used for assessing the condition of the oil insulation of power transformers. The model’s accuracy of 68.85% was achieved after optimizing the parameters of the CatBoost algorithm. The article concluded that it is necessary to increase the training sample size and improve its balance. It is inadvisable to interpret the predicted data in the field of diagnostics parameters at the available accuracy of the model’s wok.

Cross Capacitance Sensor for Insulation Oil Testing

On-site reliable transformer oil testing to assess the health of an oil-immersed transformer is a great challenge. Different sensors used for the purpose are having several limitations because of the oil and temperature. In this paper, a cross capacitance sensor cell is proposed for field testing of transformer oil which circumvents most of the limitations of thin-film chemical sensors used for the purpose. The cross-capacitance sensor cell based on the Thompson-Lampard theorem has been utilized for the first time to simulate a reliable and accurate sensor to determine degradation in insulating oil. The dielectric constant of the oil, which is determined for different oil samples experimentally, is an essential input for the finite element analysis of the sensor. Finite element analysis of the sensor cell is performed using ANSYS Maxwell software to determine its feasibility as a sensor to estimate the concentration of insulation degradation by-products dissolved in oil. The sensor is simulated to estimate the concentration of moisture and 2-FAL (2- Furfuraldehyde) in oil and to characterize aged oil. Finally, an experimental validation of the simulated sensor response for different fresh insulating oils is done. The experimental results closely match the simulation results. The sensor response is found to be approximately linear and very sensitive. Moreover, unlike thin-film chemical sensors, the same cross capacitance sensor can be used for the detection of different insulation degradation by-products dissolved in oil with proper calibration. Therefore, the proposed cross capacitance sensor cell can be used as a highly reliable on-site insulating oil degradation by-products detector.

Analysis of Partial Discharge Spectrum Based on Ultra-High Frequency Detection Method

Oil immersed power transformer is the most widely used large power transformer in power system and its insulation structure is mainly composed of oil, paper and other solid insulation materials. Partial discharge monitoring is an effective means to find dielectric faults of transformer in an early stage of development. Ultra-high frequency(UHF) partial discharge detection technology has high detection frequency and strong anti-interference ability, which is suitable for transformer online detection. In this paper, five typical transformer discharge models are built, and the discharge spectra of each model are measured by a UHF sensor. The test results show that the surface discharge and wedge discharge most occurs near the voltage peak, the discharge phase distribution of floating part discharge is very wide, the internal air gas discharge mostly occurs in the area where the absolute value of voltage increases, and the point-to-plane discharge has a typical polarity effect.

Study on noise characteristics of 500kV oil-immersed transformer under no-load voltage condition

With the expansion of urban construction scale, substation noise has attracted more and more attention. Noise characteristics and propagation of the oil-immersed transformers are made important theoretical basis of vibration and noise reduction measures. Based on the 500kV oil-immersed transformer, the noise test of transformer structures had been completed. An advanced optical fiber testing system is adopted in the test, which solves the problem of accuracy and reliability in high electromagnetic field and solid-liquid coupling environment. Time domain analysis and frequency analysis for the test data were carried out. By test and analysis, noise characteristics are obtained by the large power transformers. The frequency spectrum of noise and winding vibration in transformer insulation oil is mainly 100Hz and frequency doubling. With the increase of load, the noise presents obvious nonlinear change process.

EQUIPMENT DESIGN AND TESTING TRANSFER VOLTAGE REFERRING TO IEC 156 STANDARD USING VIRGIN COCONUT OIL (VCO) WITH OIL TEMPERATURE CONDITIONING

Isolation is a separator between conductors in electrical equipment that prevents flashover, resulting in a short circuit or electrical failure. Isolation is critical in electrical appliances, exceptionally High Voltage Power Equipment (HVPE), to ensure the safety of circuit breakers, capacitors, and transformers. In addition to being an isolator, the insulating liquid material also serves to cool the heat generated by electrical appliances. Isolator with mineral oil-based transformer has various environmental issues, including non-biodegradability, non-renewability, and rarity. Because it is environmentally safe and extensively used, virgin coconut oil (VCO) is an alternative transformer oil insulation. This study aims to determine the properties of Virgin Coconut Oil (VCO) breakdown voltage using the IEC 156 standard and oil temperature conditioning. According to the test results, the oil breakdown voltage before heating (at room temperature) is 14 kV, which is much below the IEC 156 standard, and the breakdown voltage after heating at 90 ° is 35 kV, and 110 ° is 40 kV, which is even higher than the IEC 156 requirement

Impacts of Ambient Temperature Change on the Breakdown Voltage of a Distribution Transformer

The aim of this paper is to determine the effects of ambient temperature variation on the breakdown voltage of a distribution transformer. Three different insulation oil samples (naphtha mineral, paraffin mineral and silicon base transformer oil) were collected from six distribution transformers (300 – 500 kVA) across two business units (Asaba and Ugbowo) of Benin Electricity Distribution Company during May and June, 2017. The oil samples were analysed using the 60 kV Megger OST60PB portable oil tester, to determine the trend of breakdown voltage of the oil insulation under varying temperature. A 3rd order polynomial model was deduced for each sample type with coefficient of determination within the range of 96.99 – 99.95 %. The observed average breakdown voltage is 43.6 kV (for naphtha base mineral transformer oil), 42.2 kV (for paraffin base mineral transformer oil) and 46.8 kV (for silicon base transformer oil) within the temperature range (26˚C – 32˚C). The result indicates that the breakdown voltages of the considered transformer oil types are satisfactory but the silicon base transformer oil has the best breakdown voltage.

Effect of Floating Metallic Particles in Pre-Breakdown and Breakdown Characteristics of Oil Transformer under DC Voltage

Contaminants in transformer oil insulation can float when meeting several conditions. Then, the presence of floating contaminants affects the electrical characteristics of oil insulation. Therefore, the pre-breakdown (corona) and breakdown characteristics due to metallic floating particles in transformer oil insulation would be investigated. This test used DC high voltage stress. A 56 Ω resistor was connected to the oscilloscope to detect the corona currents. The camera was used to capture the images of corona light emission. In addition, the electric field between the electrode and particles was simulated. The variables were the particle size, including its shape, and the distance between the particles and the grounded electrode. The experimental results show that the average value of corona inception and breakdown was inversely proportional to the size of floating particles. The peak value of corona current was directly proportional to the particle size. The lowest breakdown voltage was found when the particle was close to the electrode, but they were not in contact.

Investigation on Dynamic Diffusion Behavior of Furfural in Oil-Pressboard Insulation under Partial Oil Replacement Condition

Furfural, as a typical chemical indicator, is used to evaluate the aging state of the cellulose insulation in the transformer. However, partial oil replacement will lead to the loss of furfural in oil and disturb the equilibrium distribution of furfural between oil and cellulose insulation, which could affect the evaluation results of the aging state of the cellulose insulation. Unfortunately, the influence of partial oil replacement has not been focused on. Given this issue, this work studies the influence of partial oil replacement on dynamic diffusion behavior of furfural in oil-pressboard insulation. First, the dynamic diffusion behavior of furfural between insulating pressboard and oil after partial oil replacement is discussed, and the theoretical diffusion model of furfural is established. Second, based on the mass gain curve of furfural in oil, the diffusion coefficients under different oil replacement ratios are obtained. Finally, a formula for calculating the diffusion equilibrium time is proposed. This paper attempts to report a method for analyzing the impact of the oil replacement ratio on the dynamic diffusion of furfural. These findings are expected to improve the accuracy of the aging assessment results by using furfural analysis.

A modular X-pinch device for versatile X-pinch experiments at Seoul National University.

This paper describes an X-pinch device recently developed at Seoul National University (SNU). The SNU X-pinch device is designed and fabricated to accommodate various diagnostics as well as conduct versatile experiments. It is easy to change the capacitance of the pulse generator because the capacitor bank has a modular design without insulation oil or gas. This allows us to perform a variety of experiments with a wide capacitance range from 80 to 800 nF. The operating voltage of the SNU X-pinch device is controlled from 20 to 100 kV by adjusting the gas pressure inside a triggered spark-gap switch. Triggering of the spark-gap switch is synchronized with the operation of a pulsed laser to diagnose the X-pinch plasma at the proper time. A large vacuum chamber precisely machined from an aluminum mono-block is attached to the top of the pulse generator. It is designed to accommodate not only various X-pinch loads but also various diagnostic apparatus such as optical components. Initial experiments with the SNU X-pinch device have successfully generated x rays with wires of various materials and sizes. The device will be used not only to explore the dynamics of X-pinch plasmas but also as a test stand for diagnostics of high-energy-density plasmas.

Low Concentration Vegetable Oil Based Nanofluid : Dielectric properties, AC Breakdown Voltage and Kinematic Viscosity

The transformers oil acts as an insulation as well as cooling liquid of a transformer. It is very important that the transformer oil is maintained so that the oil properties are preserved with time. Petroleum-based mineral oil is widely used as insulation oil in transformer due to its excellent insulating qualities and low cost despite its’ non-biodegradable and hazardous property. This paper seeks to find an alternative of mineral oil by using palm oil based nanofluids at lower concentration values that match the IEC standards for ester oil. The nanoparticles used in this project are zinc oxide (ZnO) and zirconium dioxide (ZrO2). ZnO has conductive nature while ZrO2 on the other hand shows insulative behavior. Three different concentration value were used which were 0.0015 g/L, 0.0025 g/L and 0.005 g/L which had never been reported before. Tests performed on the samples includes AC breakdown, dielectric properties and kinematic viscosity. Research outcome shows an outstanding result at optimum value in improving the measured properties at these low nanofluid concentrations. Reducing the amount of nanoparticles use also means saving cost and providing a more eco-friendly solution.

Effect of purification process on the thermal conductivity and breakdown voltage of inhibited, isoparaffinic transformer oil used in electric train

Presence of water content or moisture promotes premature thermal aging which hampers the properties of inhibited, isoparaffinic transformer oil used in electric multiple unit (EMU) train. Unpurified aged oil with high water presence is collected from the traction transformer and contaminants is removed using Double-Stage Vacuum Insulation Oil Regeneration Filtration Machine to produce purified aged oil. New transformer oil is selected as a control sample. The objective of this study is to investigate the effect of oil purification process on the thermal conductivity and breakdown voltage of the oil samples. Thermal conductivity measurement was done from temperatures of 30°C to 70°C. Dielectric characteristics are shown by analyzing breakdown voltage. Unpurified oil shows an increment from 1.54% to 3.13% as compared to new oil in response to temperature variation whereas purified oil has the lowest thermal conductivity value. However, breakdown voltage of purified oil is higher than unpurified oil and slightly lower than new oil. From this, it can be inferred that presence of water gives positive impact towards thermal properties and vice versa to dielectric properties. A relationship between thermal conductivity, breakdown voltage and presence of water has been deduced at the end of the study.

Measurement of Tan-delta and DC Resistivity of Synthetic Ester Based Oil Filled with Fe2O3, TiO2 and Al2O3 Nanoparticles

ABSTRACT The dielectric properties of insulating liquids are very important for their application as insulation and coolant in electrical devices like transformers. It is important to monitor the health condition of transformers for uninterrupted and economical power supply. For this purpose, the simple insulating materials like pressboard and mineral oils are used. This paper presents an eco-friendly alternative to mineral oil in the form of the synthetic ester oil-based nanofluids. This paper aims to present the effect of nanoparticles on the dielectric dissipation factor and electrical resistivity of ester-based oil. In this paper, we are testing synthetic ester oils for DC resistivity and dielectric dissipation factor (Tan-delta) at different temperatures starting from room temperature up to 80°C by incorporating nanoparticles with 0.02 weight% concentration. Nanoparticles used in this study are Fe2O3, TiO2 and Al2O3. Synthetic ester oil is used as the base oil for testing. These oils are manufactured from raw materials that are basically formed by combining acids and alcohols. The heating chamber is used to heat the oil for different temperatures. Insulation resistance (IR) tester and oil dissipation factor meter are used to determine DC resistivity and dielectric dissipation factor (DDF) of simple synthetic ester oil and nano oil respectively. This paper presents the effect of nanoparticles and temperature on dielectric properties of synthetic ester-based oils.

DIELECTRIC OIL`S TEST MACHINE WISH VOLTAGE RISE ELECTRONIC MODULE

For test operations according to the liquid dielectric breakdown voltage measurement method we use high voltage machines that consist of high-voltage step-up transformer, voltage rise block, test cell with electrodes and so on. Described dielectric oil's test machine UIM – 90 with electromechanical voltage rise block. Cause of hard requirements in specification documents about voltage sine wave form on cell's electrodes, we performed field tests for UIM – 90 that help to evaluate the mains voltage impact on the test voltage distortion and measurement accuracy. Was discovered that during usage of electromechanical voltage rise block voltage steps disrupt sine wave’s form proportionally to step-up transformer’s transformation coefficient. Performed analysis of this block’s construction and established that usage of ЛАТР and mechanical voltage controller could lead to additional sine’s wave disruption. Decided to develop electronic voltage rise block which will allow to get rid of mains influence on test data. Created the algorithm of wave shaping from microcontroller, which generates voltage ramp to the amplifier representing pulse width modulator, then to the step-up transformers cascade. Proposed to use additional transformer for level matching of amplifier’s output voltage and main high voltage transformer’s input voltage. Presented flow sheet for UIM – 90 with electronic voltage step-up block and cascading start ofstep-up transformers. Provided voltage oscillograph trace and it spectrograph on the main transformer’s primary side, received due to the implementation of developed electronic voltage step-up block, prove that voltage sine wave form doesn’t rely on mains quality. After upgraded UIM – 90 and it world analogues technical parameters analysis we could make a conclusion about it competitive capability on global level.

Research on operation characteristics of UHV converter valve hall based on intelligent image processing and 3D modeling technology

There are many power equipments in the UHV valve hall, including the converter transformer, converter valve tower, all kinds of bushing, tubular bus. The operation condition monitoring of the above main equipment mainly includes electrical performance parameter measurement, oil and gas insulation medium performance parameter measurement and other means. This paper mainly introduces a monitoring method for the operation status of converter valve hall from the perspective of image processing technology. The technology mainly includes: 1) the application of intelligent image processing technology to identify and classify the database of infrared thermal imager and ultraviolet imager; 2) the real-time on-line measurement for the insulation distance of typical fittings through Kalman filter technology, including the measurement of the hottest temperature The insulation distance between partial discharge point and zero potential grounding point; 3) the electric field simulation model of typical main equipment in valve hall is established based on three-dimensional modeling technology of finite element method, and the surface electric field distribution of key main equipment fittings is obtained. Combined with the image database information, insulation distance information and typical main equipment electric field distribution information, the operation state parameters are effectively obtained, and the intelligent algorithm is applied to automatically evaluate its operation state, discover the latent fault and locate the positive fault, so as to provide effective data support and the protection strategy for the main equipment operation and maintenance.

Towards Precise Interpretation of Oil Transformers via Novel Combined Techniques Based on DGA and Partial Discharge Sensors.

Power transformers are considered important and expensive items in electrical power networks. In this regard, the early discovery of potential faults in transformers considering datasets collected from diverse sensors can guarantee the continuous operation of electrical systems. Indeed, the discontinuity of these transformers is expensive and can lead to excessive economic losses for the power utilities. Dissolved gas analysis (DGA), as well as partial discharge (PD) tests considering different intelligent sensors for the measurement process, are used as diagnostic techniques for detecting the oil insulation level. This paper includes two parts; the first part is about the integration among the diagnosis results of recognized dissolved gas analysis techniques, in this part, the proposed techniques are classified into four techniques. The integration between the different DGA techniques not only improves the oil fault condition monitoring but also overcomes the individual weakness, and this positive feature is proved by using 532 samples from the Egyptian Electricity Transmission Company (EETC). The second part overview the experimental setup for (66/11.86 kV–40 MVA) power transformer which exists in the Egyptian Electricity Transmission Company (EETC), the first section in this part analyzes the dissolved gases concentricity for many samples, and the second section illustrates the measurement of PD particularly in this case study. The results demonstrate that precise interpretation of oil transformers can be provided to system operators, thanks to the combination of the most appropriate techniques.