Insulation Oil Research Articles

РАЗРАБОТКА ПРОГРАММЫ «ХРОМАТИК» ДЛЯ ОЦЕНКИ СОСТОЯНИЯ ТЯГОВЫХ ТРАНСФОРМАТОРОВ

The paper deals with the urgent problem of preventing failures of oil-filled railways equipment by means of non-destructive methods of diagnostics and early detection of pre-failure conditions. A computer program based on dissolved gas analysis for assessing and predicting the power transformer’s state was proposed and registered. The objects of the study are traction substation’s transformers located on the Far Eastern Railway of Russia. The dissolved gases concentration has been analyzed for an eight-year observation period. The problem of the state of oil insulation predicting is solved by Gaussian distribution applying. The developed software can be used at the digital traction substations as the predictive analytic block, which corresponds to the current digitalization trend.

The problem of determining the antioxidant additive in transformer oil by chromatographic methods

THE PURPOSE. Transformer oil is widely used in high-voltage electrical equipment and acts as a dielectric and also as a cooling medium. It consists of a complex mixture of hydrocarbon compositions with various impurity compounds. During the operation of oil -filled electrical equipment under the influence of the technological operating conditions of high -voltage devices, aging of both transformer oil and solid insulation occurs. In this case, the dielectric properties deteriorate, which can damage the transformer equipme nt. METHODS. To increase the service life of oil-filled electrical equipment, an antioxidant additive is introduced into the transformer oil at the stage of its manufacture, which is most often used as ionol, the concentration of which must be constantly controlled by various instrumental methods. To determine the antioxidant additive in transformer oil, a sample preparation system is used based on liquid-phase extraction with selective solvents, which are used as aliphatic alcohols of various physical and chemical nature. RESULTS. It has been established that ethyl alcohol, which is widely used in the sample preparation system for liquid extraction of ionol, contains a significant amount of water, which has a negative effect on the process of ionol extracti on from transformer oil. In addition, the composition of ethyl alcohol contains impurity substances that can have a negative effect on the process of liquid-phase extraction of ionol from transformer oil. The generalized data on the physicochemical properties of extractants used to extract ionol from transformer oil are presented. CONLUSION. It has been shown that butanol is the most promising organic solvent for the extraction of ionol, which has a higher boiling point compared to ethyl alcohol and contains a small amount of water. It was found that the selectivity of the chromatographic separation of butanol components with an elevated column temperature increases. At the same time, the separation efficiency increases as the number of theoretical plates per meter of chromatographic column increases. As the temperature of the capillary column increases, the symmetry of the chromatographic peaks of the separated components also increases.

Mechanistic studies of gene delivery into mammalian cells by electrical short-circuiting via an aqueous droplet in dielectric oil.

We have developed a novel methodology for the delivery of cell-impermeable molecules, based on electrical short-circuiting via a water droplet in dielectric oil. When a cell suspension droplet is placed between a pair of electrodes with an intense DC electric field, droplet bouncing and droplet deformation, which results in an instantaneous short-circuit, can be induced, depending on the electric field strength. We have demonstrated successful transfection of various mammalian cells using the short-circuiting; however, the molecular mechanism remains to be elucidated. In this study, flow cytometric assays were performed with Jurkat cells. An aqueous droplet containing Jurkat cells and plasmids carrying fluorescent proteins was treated with droplet bouncing or short-circuiting. The short-circuiting resulted in sufficient cell viability and fluorescent protein expression after 24 hours’ incubation. In contrast, droplet bouncing did not result in successful gene transfection. Transient membrane pore formation was investigated by uptake of a cell-impermeable fluorescence dye YO-PRO-1 and the influx of calcium ions. As a result, short-circuiting increased YO-PRO-1 fluorescence intensity and intracellular calcium ion concentration, but droplet bouncing did not. We also investigated the contribution of endocytosis to the transfection. The pre-treatment of cells with endocytosis inhibitors decreased the efficiency of gene transfection in a concentration-dependent manner. Besides, the use of pH-sensitive dye conjugates indicated the formation of an acidic environment in the endosomes after the short-circuiting. Endocytosis is a possible mechanism for the intracellular delivery of exogenous DNA.

Parametric optimization of process parameters for Electric discharge Machining of Tungsten carbide (93% WC and 7%Co)

Abstract Nowadays there is a huge demand of High Strength Temperature Resistance (HSTR) alloys such as titanium, carbide, nimonics and ceramics in aerospace, defence and electronics. Among these alloys machining of tungsten carbide alloy is of interest, because of its numerous applications. Complex shapes of tungsten carbide are not generally made by traditional manufacturing process. To machine tungsten carbide with high accuracy, non-traditional machining process like Laser beam machining, Electron beam machining and Electrical discharge machining are a proper choice. In the present paper, the authors have machined Tungsten carbide (93% WC and 7%Co) with copper electrode. The machining is performed on EDM MODEL 500 X 300 ENC with VELVEX EDMVEL-2 as dielectric oil. The 17 experiments are carried out based on RSM (Box-Behnken) method. Further, in order to find the optimum combination grey relational approach is used. The results showed that pulse-on-time of 40μs, pulse-off-time of 2μs and current of 8A are optimum combination for machining of Tungsten carbide (93% WC and 7%Co). Lastly, the confirmation experiment has been conducted.

Electric field enhancement control in active junction of IGBT power module

Dielectric liquids are incompressible, able to fill voids and have selfhealing effect and hence are being considered as alternative encapsulation materials to establish power electronics at ambient high pressure at subsea conditions. In a long-term endurance test, insulated-gate bipolar transistor (IGBT) chips subjected to 6.5 kV DC stress in dielectric oil environment was reported to have failed after less than one week in operation. A critical look at the failed objects revealed contamination fibres at the surface and around the high field regions. This paper presents the numerical simulation of field distribution around a conducting fibre at the surface of the IGBT chip. It also evaluates the influence of the nature of the encapsulation material on the integrity of power electronic modules using a long-term experiment at a medium elevated temperature for high and low relative humidity operated close to service load using IGBT relevant chips. Finite element method (FEM) calculations show how the high field region can be shielded from impurities that can easily trigger partial discharge (PD) and breakdown. The simulation suggests that coating the surface of the module with a thin polymer layer with a thickness of 20 μm or more could be sufficient to improve the reliability of the encapsulation system. Additional polymer coat with thickness 27 μm on the chip made the system survive without failure for 67 weeks under test and dry operating condition. Meanwhile, thick coating such as silicone gel protected the object longer under higher relative humidity.

Toxicity test for Fuller’s earth contaminated with dielectric oil using eisenia foetida earthworms and soils with different carbon contents

Fuller’s earth is an adsorbent material used in the electric industry for dielectric oil regeneration. The high amount of polyaromatic hydrocarbons removed from oil and adsorbed in the Fuller’s earth makes this material a hazardous waste. It is necessary to implement a toxicity test and apply a suitable treatment to safely dispose of this waste in a landfill or repurpose it for reuse. In this paper, the toxicity of Fuller’s earth contaminated with dielectric oil is assessed before and after treatment. The toxic potential of the Fuller’s earth and the dielectric oil extracted through decontamination processes was evaluated in two types of soil with different carbon contents, analyzing the effects on the test organisms, Eisenia Foetida earthworms. These tests showed that decontaminated Fuller’s earth is non-toxic, and that the toxicity of the contaminated Fuller’s earth, or its extracts after treatment, represented by the median lethal concentration (LC50) depends significantly on the type of soil used.

Simulation effect of SiO2 nanoparticles on the water molecules diffusion inside insulating oil at different temperatures

The performance of transformer insulating oil will gradually decrease with the long-term operation of transformer. Previous researches have shown that temperature is one of the important factors affecting the insulation performance of transformer insulation oil, and the addition of nanoparticles can effectively improve the insulation properties of oil. In order to further reveal the influence of temperature and nanoparticles on the diffusion ability of water molecules in insulating oil, the diffusion behavior of water molecules in pure oil model (AW-1) and model (AW-2) containing nano-SiO2 particles at 303K, 323K, 343K, 363K and 383K temperatures are studied in this paper. The simulation results showed that nano-SiO2 particles can effectively reduce the influence of temperature on the diffusion behavior of water molecules in oil. In two models, the free volume fraction of moisture in oil will be improved with the increase of temperature, which provides more space for the movement of water molecules. However, in the AW-1 model, the growth rate of the free volume fraction is around 2.2 %, while that in the AW-2 model is around 1.5 %. Moreover, according to the analysis of the radial distribution function (RDF) between different atoms in the two models, the covalent bond and the hydrogen bond between the atoms weakens due to the increase of temperature. In addition, with the increase of temperature, the interaction energy between water molecules and oil gradually decreases in two models. In the AW-1 model, with the increase of temperature, the reduction rate of interaction energy is about 4.5 %, in the AW-2 model, the reduction rate of interaction energy is about 2.5 %, which indicates that the influence of temperature on the AW-2 model is smaller. Therefore, adding nanoparticles to the oil can effectively restrain the movement of water molecules in the oil, so as to improve the insulation performance of transformer insulation system.

Effect Of Phenol Addition To Transformer Oil Breakdown Voltage

The failure of transformer insulation often occurs due to various kinds of things, one of which is failure in the oil isolation caused by the condition of oil that has been dirty or has been contaminated with other particles in the transformer. Phenol is a chemical that can purify or cleanse particles or impurities that are in used transformer oil, so that it can increase the breakdown stress on used insulation oil. Phenol contains acid which can attract particles and impurities in the transformer oil which results in a decrease in the breakdown strength of the insulating oil. The results of testing of used isolation oil by adding phenol as much as 10, 15 and 20 ml showed an increase in the value of breakdown voltage with a distance of 2.5 mm ball inlet electrode. Translucent stresses that meet the SPLN standard 49-1: 1982, that is ≥ 30 kV at intervals of 2.5 mm were obtained by adding 20 ml of phenol to the volume of used 400 ml transformer oil

Development and Testing of a Wireline-Deployed Positive-Displacement Pump for Late-Life Wells

SummaryWhat do you do after plunger lifting? What if lift gas is not readily available or your liquid level is around a bend? What can you do with a well that has low reservoir pressure, liquid-loading trouble, and fragile economics? Do you give up on the remaining reserves and advance to plugging and abandonment? These questions were considered, and the answers were found to be unsatisfactory. This paper will describe the development and testing of a novel wireline-deployed positive-displacement pump (WLPDP) that was invented to address these challenges.Artificial-lift (AL) pumps have historically been developed with high-producing oil wells in mind. Pumps for late-life wells have mostly been repurposed from these applications and optimized for reduced liquids production. The WLPDP development began with the constraints of late-life wells with the goal of addressing reserves that conventional AL methods would struggle to produce profitably. Internal and industry-wide data were first reviewed to determine what WLPDP specifications would address the majority of late-life wells. The primary target was gas wells, although “stripper” oil wells were also considered. The resulting goal was a pump that could deliver 30 BFPD from 10,000-ft true vertical depth (TVD).The pumping system must be cost-effective to be a viable solution, which led to several design boundaries. Pumps fail and replacement costs can drive economics, so the system must be deployable/retrievable through tubing. The majority of new onshore wells have tortuous geometries, so the system must be able to function at the desired depth despite them—without damaging associated downhole components. The system should use as many off-the-shelf components and known technologies as possible to reduce development costs and encourage integration. Finally, the pump should be able to handle a variety of wellbore liquids, produced gases, and limited solids.The WLPDP was designed to meet the established specifications and boundary conditions. The 2.25-in.-outer-diameter (OD) pump is deployed through tubing. and powered with a standard wireline (WL) logging cable. The cable powers a direct-current (DC) motor that drives an axial piston pump. The piston pump circulates a dielectric oil between two bladders by means of a switching valve. When each bladder expands, it pressurizes inlet-wellbore liquids, pushing them out of the well. Produced gas flows in the annulus between the tubing and production casing. The intake/discharge check valves and bladders are the only internal pump components that contact the wellbore fluids.The WLPDP system was able to meet the design-volume/pressure specifications in all orientations, as confirmed through laboratory and integration testing. Targeted studies were conducted to verify/improve check-valve reliability, gas handling, elastomer suitability, and cable-corrosion resistance. The results of these and related studies will be discussed in the paper.

Nanofluid from Palm Kernel Oil for High Voltage Insulation

A clean alternative insulating oil has been the quest of researches over the years due to non-degradability of mineral oil and safety issues. With the application of nanoscience and nanotechnology, the potential of transformer oil-based nanofluids has been thoroughly investigated with signs of significant improvement. Attention was placed on natural ester as a green alternative and it was realized that it has the potential to become a replacement for mineral oil. However, for natural ester-based nanofluids, the performance analysis is not well explored and there is still room for more investigations. This paper focused on the improvement of the physicochemical properties, dielectric loss and breakdown voltage of palm kernel oil ester using Al2O3 and TiO2 nanoparticles. The nanoparticles were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Scanning electron microscopy (SEM) equipped with electron dispersive X-ray analysis (EDX). The physicochemical properties, relative permittivity, dielectric loss, and high voltage DC conductivity of the nanofluid samples were studied with varying weight percentages of Al2O3 and TiO2 nanoparticles ranging from 0.2 wt% to 1 wt% in a step of two to understand the behaviour of the materials. The adequacy of the fluid samples as an electrical insulating fluid in oil-filled high voltage (HV) electric equipment was explored and compared. For both types of nanoparticles, the dielectric loss was observed to decrease at 1 wt% but with a more noticeable decrease when considering Al2O3 nanoparticle. Measurement of DC electrical breakdown voltage of the ester-based nanofluids revealed that the dispersion of nanoparticles in the fluid result in an increase in the breakdown voltage of the base fluid with the optimum value obtained at 0.6 wt%. The study indicated a decrease in the dielectric loss of the nanofluid sample and exhibited improved breakdown voltage when compared with the base alkyl ester.

Effective removal of toluene at near room temperature using cyclic adsorption-oxidation operation in alternative fixed-bed plasma-catalytic reactor

This work investigated the removal of toluene using cyclic adsorption/oxidation operation in a fixed-bed dielectric barrier discharge (DBD) plasma-catalytic reactor containing Pd/ZSM-5 catalyst. The modification of ZSM-5 with Pd catalyst (2 wt %) substantially improved the adsorption capability for toluene. The catalyst adsorbing toluene was readily regenerated during the plasma-catalytic oxidation step. The synergistic effect of the catalyst promoted the toluene oxidation process as well as improved the selectivity towards CO2. As a method of reducing the energy in generating plasma, two cases (when the ground electrode was exposed to the external air and when the ground electrode was immersed in insulating oil) were compared. No micro-discharge occurred outside the ground electrode surface after oil jacketing, which prevented NOx and ozone from forming, improved energy efficiency, and promoted CO2 selectivity to 91%. The energy consumption with the oil insulation was 14.5 J/L, while that without it was 58.0 J/L. The catalyst was characterized using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).

Experimental Study on the Gas Bubble Temperature Around an Arc Under Insulation Oil

The internal temperature of a gas bubble caused by a fault arc is a key basic parameter for investigating the bubble behavior and the pressure rise inside oil-filled power equipment. Due to the constraints imposed by the measurement methods and experimental conditions, this temperature has always been estimated as a constant value of 2000 K in past decades. In this letter, we present direct experimental evidence of the gas bubble temperature around an arc. A large oil-filled transformer was reformed and used to conduct arcing fault tests. A sapphire fiber optic infrared thermometer was established and used to detect the internal gas bubble temperature. The experimental results confirm that this internal temperature is not constant but rather varies over a wide range from 2100 K to 1500 K, plummeting with rapid bubble growth and then exhibiting small variations until arc extinction. Furthermore, the bubble growth process throughout the arc duration can be approximately regarded as first polytropic and then isothermal.

Effects of Oil Type on Sterol-Based Organogels and Emulsions

The present study investigates the effect of oil type on the formation, morphology and mechanical properties of phytosterol-based organogels. The formation of organogels can be satisfactorily predicted with a criterion based on Hansen Solubility Parameters (HSPs), provided that the sterol and sterol ester in these systems assemble as tubules. When structures other than tubules are formed, the predictability of the HSP-based criterion becomes void. In cases where organogelling occurred, the morphology and mechanical properties of the tubular network of the gels and water-in-oil emulsions were investigated. The findings revealed that the structure of the tubular network formed in oils with different compositions, could be grouped based on the dielectric constants of the oils. Curly and bundled tubules which formed networks, were observed in gels prepared with low dielectric constant oils (i.e. decane and limonene). For oils with a moderate dielectric constant (i.e. castor oil and sunflower oil), the tubules became less curly and straighter. Upon increasing the dielectric constant of the oil (eugenol), individual tubules were observed next to the bundled tubules. The results showed that straighter, bundled tubules are associated with firmer gels, whereas less straight (i.e. curly) tubules rendered weaker gels. The tubular network of the water-in-oil emulsions obtained for oils with a low dielectric constant appeared more open with straighter tubules. For oils with relatively high dielectric constant, the water-in-oil emulsions lost most of their tubular structure and only a few tubules could be observed. In the presence of emulsion droplets fewer tubules are formed, resulting in weaker networks.

Evaluation of Abnormal Conditions of Oil-impregnated Insulation Papers in Aged Oil-filled Cable Joints and Terminations Removed After Service and Proposal of Classification Method for Ranking of their Abnormal Conditions

Degradation rate of electrical insulation performance of oil-filled (OF) cables has been considered small since void-less conditions are realized due to their oil-impregnated insulation systems under insulation oil pressure that exceeds atmospheric pressure. However, recently, insulation breakdowns have occurred in OF cable joints at extra-high voltage, and they were not predicted by dissolved gas analysis (DGA) of insulation oil. Therefore, it is necessary to improve the prediction accuracy of DGA for detection of partial discharges (PDs), which are known as a pre-breakdown phenomenon. Recently, it has been reported that traces of black color in oil-impregnated insulation papers are sometimes compounds of oxide sludge or copper sulfide, which were all regarded as carbonization due to PDs. Moreover, it has been reported that PD inception fields decrease with an increase in the rate of the total thickness of insulation papers with discoloration to the insulation thickness. To improve the prediction accuracy of DGA, such new findings should be taken into account when ranking abnormal conditions of insulation systems of cable joints and terminations, which gives the basic data for the prediction by DGA. In this study, abnormal conditions of oil-impregnated insulation papers were redefined and classified into trace of occurrences of PDs and two types of discoloration, and those of 264 aged OF cable joints and terminations removed after service were investigated. In addition, the above-mentioned rate was quantitatively evaluated for cable insulation systems, and locations of the abnormal conditions were investigated in detail for reinforced insulation systems. Taking these results into account, a new classification method for the ranking of abnormal conditions of oil-impregnated insulation systems was proposed.

Breakdown and streamer behavior in homogeneous synthetic trimethylolpropane triesters insulation oil

A new method, which involves the addition of alkaline Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (3 wt%) and activated clay (5 wt%) as adsorbents for homogeneous synthetic trimethylolpropane triesters (TME), is reported here to not only improve electrical properties but also to shed light on future volume production. The results show that the acid value and the dielectric loss of TME oil is successfully reduced and meets IEC 61099. The viscosity of TME approaches that of mineral oil (MO) for transformers. In addition, TME oil with antioxidants exhibits fairly good oxidation stability that is evidenced by a notably high oxidation onset temperature of 226°C, which is 39 K and 14 K higher than that of commercial natural ester oil (NEO) (187°C) and MO (212°C), respectively. Furthermore, compared with the AC breakdown voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> ) of NEO (65.3 kV) and MO (70.4 kV), the TME oil has a higher V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> =73.2 kV. Besides, the positive lightning impulse (LI) V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> and streamer behavior of TME at small gaps are comparable to those of MO and NEO. However, the negative LI V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> of TME and NEO are significantly lower than that of MO owing to the combined field variation towards the plane electrode which will facilitate the propagation of the streamer. Therefore, additives without oxygen, fluorine and chlorine should be given priority when they are used to improve the properties of insulation oil.

A comprehensive analyses of aging characteristics of oil-paper insulation system in HVDC converter transformers

This paper investigates the dissolved gases evolution in transformer oil under combined DC/AC electrical-thermal stress. Dissolved gases detected in transformer aged insulation oil reveal that oil under AC electric field combined with thermal stress can produce more dissolved gases than oil under DC electric field with thermal stress but less than the gases produced in oil under distorted AC or combined AC/DC voltage stress. This is attributed to the divergent migration properties of the charged components under different types of electric fields. To further understand this behavior, carrier recombination coefficient is proposed to explain the oil DGA results under various aging stresses. Results show that diagnostic parameters such as breakdown voltage, oil interfacial tension, and moisture content in pressboard should be used along with DGA results in order to accurately diagnose the insulation condition within converter transformers that impose a combined AC/DC voltage stress on the insulation system.

Analysis of Factors Affecting Temperature Rise of Oil-immersed Power Transformer

The key factors that affect the operation state of power transformer include thermal problem and insulation problem. It is of great significance to pay attention to the factors affecting the temperature rise characteristics of transformer to ensure its stable operation. The temperature rise characteristic model of transformer is established to explore the possibility of replacing mineral oil with plant insulation oil FR3 in this paper. On the basis of calculating the influence of ambient temperature change of external heat source on transformer temperature rise, the relative life loss rate of transformer under different ambient temperature is calculated. The results show that FR3 vegetable oil can replace mineral oil in terms of temperature rise. The temperature of the transformer core and winding hot spot increases with the ambient temperature. When the ambient temperature exceeds 293K, the relative life loss rate of the transformer increases very quickly. Therefore, the transformer should not be kept in an environment where the temperature exceeds 293K for a long time.

DC characterization of isoparaffinic insulation oil

Converter transformers in HVDC stations are subject to both AC and DC stresses. With new oils entering the market it is important that these are characterized both for AC and DC. This paper focuses on DC characterization of one such oil, which is an isoparaffinic oil produced using a gas to liquid production process. The results are compared to mineral oil as reference. The isoparaffinic oil is shown to have a very high resistivity. In fact, the resistivity is so high that it is more resistive than impregnated pressboard with low moisture content. This is a dielectric risk which must be considered if the oil is to be used in converter transformers.

Developing eco-friendly nanostructured oil: Partial discharge and breakdown voltage characterization of transformer corn oil

This paper focuses on characterization of a natural ester oil, based on corn, which has been nanostructured by carbon quantum dots (CQD) decorated nano fillers. Partial discharge (PD), lightning impulse (LI) and AC power frequency breakdown strength of corn oil, pure and nanostructured by CQD-treated SiO 2 and TiO 2 nanoparticles, are measured for different concentration of nanofillers with mass fractions of 0.01, 0.05 and 0.1. It is shown that the addition of CQD-treated SiO 2 nanofillers improve considerably oil insulation performance already at very low nanoparticle concentration, which indicates promising potentiality for transformer insulation applications, from compact design to long-term performance.

OCCURRENCE, COMPOSITION PROFILES AND POTENTIAL RISK ASSESSMENT OF POLYCHLORINATED BIPHENYLS (PCBS) IN TRANSFORMER OILS

One of the most common problems encountered in everyday life is the pollution of the environment. Therefore, regardless of the nature of the daily activities of the population, this destructive effect of the natural balance finds its origin perhaps in the lack of capacity over time to treat the problem of waste (industrial and domestic) as it should. Although important steps have been taken in this regard, and prevention and control rules have been imposed in most countries of the world, these steps must be supported by all socio-economic / political components through clear measures, anchored to global developments. There are among these generic sources of pollution, which are referred to above, processes that requires high power equipment (generators, transformers, etc.) or hydraulic who which also requires thermal insulation fluids. The aim of this study is to investigate the polychlorinated biphenyls (PCBs) presence in the dielectric oil of power transformers. In this matter, fifteen samples were collected from transformer oils, in the summer of the year 2017, and analyzed from a physicochemical point of view. A more specific aim was to corroborate the findings regarding the amount of chlorine in oil samples with the age of the power transformer using statistical methods. The cluster's analysis indicated that the investigated samples are clustered into four major groups, providing useful information for further studies on PCBs mobility in the environment.