Power Transformer Applications Research Articles

Experimental studies on insulating oils for power transformer applications

Abstract In recent days, ester-based alternatives like natural and synthetic oils are preferred as an alternative to mineral oil by the power industry due to its higher bio-degradability, superior thermal conductivity, and fire resistance than mineral oil. In addition to this, blended oils are quite attractive because of its low dielectric loss and a low ratio of degradation. The present research deals with the experimental studies on different insulating oils like mineral oil, synthetic ester oil, coconut oil, blended oils, and nanofluids, which are developed from ZnO and TiO2 nanoparticle doped at 0.01 vol% in different insulating oils through ultrasonication process. In this experiment, the critical properties like electrical and physicochemical properties are examined according to International Electrotechnical Commission and American Society for Testing and Materials standards. Results show that ZnO and TiO2 nano-powder enhances the AC breakdown voltage (BDV), dielectric permittivity, and DC resistivity properties of different insulating oils with improved flash and fire resistance. Remarkably, it is found that mineral oil-based TiO2 nanofluid shows an enhancement of 55.8 % in AC BDV, 9.1 % in permittivity, and 15 % in flash resistance. Moreover, mineral oil based ZnO and TiO2 nanofluid results exhibit remarkable decrement in loss tangent with increased DC resistance property. Finally, it is observed that the influence of TiO2 nano-powder at 0.01 vol% remarkably enhances the electrical and physicochemical properties in different insulating oils compared to ZnO nanofluids. Hence, mineral oil and green insulating based synthetic ester oil (which is based on TiO2 nanofluids) have been considered as a potential candidate to make alternatives to traditional insulating oil for power transformer applications. The findings offer critical insights for the future of transformer insulation systems, guiding industry standards and fostering innovation in material science.

Investigation of transformer oil aging using no-core optical fiber (NCF) sensor

Transformer oil plays a crucial role in insulation and cooling within high-voltage transformers, but it degrades over time. This research proposes a durable sensor capable of detecting the refractive index (RI) of transformer oil when it exceeds the RI of the sensor structure, known as high refractive index (HRI) sensing. The study utilizes a no-core optical fiber (NCF) to monitor the quality of transformer oil. In this setup, single mode fiber (SMF) is employed as both the input and output of the NCF, forming an SMF-NCF-SMF (SNS) sensor. To date, to the use of an NCF in the SMF-NCF-SMF scheme has not been reported for high RI fiber sensing and transformer oil degradation detection. Additionally, this study provides an analysis of the influence of different diameters and lengths of NCF on the sensor’s sensitivity. The HRI sensing performance of the sensor was evaluated both numerically and experimentally by observing power spectrum changes due to leaky modes interference in response to varying transformer oil RI values from 1.4600 RIU to 1.5500 RIU. The NCF, with a geometry of 1 cm in length and 100 μm in diameter, demonstrated remarkable sensitivity, achieving up to 88.285 dBm/RIU for HRI values within the specified range. The sensor effectively discerned various aging levels of transformer oil in power transformer applications. Additionally, since the NCF structure is entirely composed of silica-based materials, it exhibited significant temperature resistance. These characteristics make the SNS structure well-suited for reliable deployment in challenging thermal environments.

Experimental Aging of three-element Mixed Oil Insulation and Pressboard for Power Transformer Applications

Experimental Aging of three-element Mixed Oil Insulation and Pressboard for Power Transformer Applications

Performance evaluation of natural Olea europaea (olive oil)-based blended esters with butylated hydroxyanisole and butylated hydroxytoluene: optimization using response surface methodology.

For power transformer applications, this study explores an alternative insulating liquid. With this aim, edible natural esters such as refined Olea europaea (olive oil), rice bran oil, soya bean oil, sunflower oil, and corn oil are investigated as suitable replacements for the mineral oil (MO) used in the transformer. In addition, olive oil and other natural esters are incorporated into the blend for further analysis to obtain a better insulating medium. Blended natural esters were also tested for performance enrichment by antioxidant inclusion. Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) were chosen as antioxidants for this study. In this study, we aimed to investigate the role of key input factors [A-speed, B-time, and C-temperature] on the output response [Y-breakdown voltage]. It was determined that the optimal conditions for [Y] are [A-699.91 rpm, B-49.95 min, and C-88.75 °C]. In order to ensure the desirable properties, the natural esters were subjected to certain experimentations such as breakdown voltage (BDV), viscosity, fire point (FeP), and flash point (FhP). From the results, it is observed that the natural esters and blended natural esters can be used in the transformer as an alternate insulating medium and that the antioxidants have a significant effect on the properties of natural ester combinations.

Physical and Electrical Breakdown Characteristics of Oil-Impregnated Kenaf Paper with the Introduction of External PVA for Transformer Application

This work examines the physical and electrical breakdown characteristics of kenaf paper coated with Polyvinyl Alcohol (PVA) for application in power transformers. The paper was made from kenaf bast fibers using the soda pulping method, whereby the pulps were subjected to 12,000 beating revolutions. PVA with weight percentage concentration up to 6% was introduced to the beaten kenaf through a spin coating approach. The structure of the kenaf paper was examined through Scanning Electron Microscopy (SEM). The physical properties examined were apparent density, Tensile Index (TI), Burst Index (BI), and Tear Index (TeI), while AC breakdown voltage and strength were analyzed for the electrical property. It is found that the beating and external PVA improve the kenaf paper’s apparent density, TI, BI, and AC breakdown strength while the TeI decreases.

Testing of Palm Oil-Based Electric Power Transformer Insulation Oil as a Renewable Energy Source

Reducing petroleum resources and environmental problems, alternative insulating oils with biodegradable characteristics have become an alternative. Esterification of palm-based oil is expected to provide better and optimum electrical properties. The esterification of palm oil will be carried out as a test sample and observed for its electrical, physical and chemical properties such as PD characteristics, breakdown voltage, dissipation factor, viscosity, flash point, etc. The effect of thermal aging on oil samples will also be carried out to simulate real situations in power transformer applications. Then after obtaining the best formulation from the sample it will be used as insulating oil in electric power transformers (100kVA). The purpose of this research is to apply esterified palm oil as an electric power transformer oil. The method used in this research includes field research. Field research includes taking oil samples, measuring the breakdown voltage of transformer oil, and the color of transformer oil. The results obtained are insulating oil for electric power transformers based on palm oil. Palm oil has the advantage of being an environmentally friendly, biodegradable and renewable oil compared to the transformer oil used today which is based on petroleum. With the realization of transformer oil based on palm oil, it is hoped that it can provide great economic opportunities for Indonesia as one of the largest palm oil producers in the world and can also provide added value and increase the competitiveness of the palm oil industry in the future.

Natural Esters for Green Transformers: Challenges and Keys for Improved Serviceability

The service of mineral insulating oils for power transformer insulation and cooling aspects cannot be disavowed. However, the continued use of mineral oils is questionable due to environmental unfriendliness and the divestment from fossil fuels. This has provoked the quest for green alternative insulating liquids for high-voltage insulation. Natural esters are among the remaining alternatives that are renewable and environmentally friendly. Regardless of their environmental and technical merits, natural esters have some limitations that are slowing down their total acceptance by transformer owners and utilities. Critical limitations and concerns include esters’ pour point, viscosity, oxidative stability, and ionization resistance. In this work, the state of the art of “natural esters for transformers” is explored with the aim of potential improvements. The sections of the article are geared towards technical viewpoints on improving the overall workability and serviceability of natural esters in high-voltage applications. A comprehensive review of the existing literature is achieved, based on performance improvements of the natural ester using “additives” and “chemical modification”. The authors hope that this report may be helpful to transformer owners as well as influence the progression of natural esters for power transformer applications.

Influence of Emerging Semiconductive Nanoparticles on AC Dielectric Strength of Synthetic Ester Midel-7131 Insulating Oil.

Exploring impressively effective dielectric nanofluids for transformers to improve dielectric strength and thermal stability is indispensable. It is crucial to determine the modification mechanism of dispersed nanomaterials in insulating oil for operative applications in power transformers. This paper aspires to authenticate the experimental evidence of the enhancing AC dielectric strength of synthetic ester Midel-7131 using two newly introduced semiconductive nanoparticles, CdS and Co3O4, and uncover the potential reasons for enhanced AC dielectric strength. The AC breakdown voltage (BDV) of synthetic ester and nanofluids was investigated and statistically evaluated. The mean AC breakdown voltage of SE/CdS and SE/Co3O4 was increased by 31.9% and 31.3%, respectively. The augmentation in AC breakdown strength is possibly due to the facilitated charge-scavenging ability owing to the large specific surface area and wide bandgap. Simultaneous thermogravimetric analysis, differential scanning calorimetry, and derivative thermogravimetry analyses (TGA–DSC–DTG) confirmed that the initial decomposition temperature was high and heat dissipation was low, indicating that the nanofluids were thermally stable in both air and nitrogen. Hence, emerging semiconductive CdS and Co3O4-based nanofluids of synthetic ester possess remarkable dielectric strength and thermal stability enhancement for their application in power transformers.

Understanding the Lightning Impulse Discharge Characteristics of Nano Silica Modified Sunflower Oil for High-Voltage Insulation Applications

Vegetable oils with nanotechnology added to them are a possible replacement for mineral oils in power transformer applications today. Because of the size and production cost reductions as well as the oil's high level of biodegradability, this could result in an increase in the dielectric strength of insulating fluid. Since transformers are mainly used for outdoor applications, understanding the capability of insulating fluid to withstand lightning discharge is a vital issue. This study used experimental analysis to compare the lightning discharge performance of pure sunflower oil and sunflower oil modified with SiO2 (Nano) at various weight-per-volume concentrations of 0.01 %, 0.05 %, and 0.1 %. This experimental work was conducted with 1.2/50 µs of standard lightning impulse voltage with positive polarity. The result illustrated that the nano-modified sunflower oil had greater lightning impulse withstand strength than the pure sunflower oil.

Analysis of the Impregnation Process of Cellulose Materials by Using Ester-Based Liquids and Mineral Oil

Nowadays, new alternative of dielectric liquids with biodegradable characteristics has been considered to replace conventional mineral oil in both distribution and power transformer applications. However, there are some manufacturing processes that need to be modified to incorporate these ecological fluids, mainly in power transformers. Ester liquids, either natural or synthetic, show higher viscosity than mineral oil; therefore, a significant impact on the impregnation process of insulation materials is expected. In this work, the impregnation process of cellulose insulation is investigated by using three different liquids: natural ester (NE), synthetic ester (SE), and mineral oil. Laboratory tests were carried out using insulation blocks and pressboard samples to evaluate the influence of each fluid in the cellulose material. It is shown that the impregnation process with ester liquids is longer than mineral oil, at room temperature; however, it could be reduced by increasing the temperature of the ester liquid.

Single-Mode-Multimode Silica Rod-Single-Mode High Refractive Index Fiber Sensor

This paper reports a robust high refractive index (RI) sensor based on a multimode silica rod structure. The sensor was fabricated by splicing a segment of multimode silica rod between two single-mode fiber (SMF) leads. The measurement of high-RI is realized by monitoring the change of power spectrum caused by the reaction of leaky modes to different surrounding high-RI. The 0.5-cm long multimode silica rod sensing element exhibits a sensitivity of up to 115.12 dBm/RIU for high-RI ranging between 1.450 and 1.531. The sensor also demonstrated its potential in power transformer application by distinguishing various ageing levels of transformer oil. The leaky modes mechanism in all-silica based structure is essentially temperature insensitive, and therefore very practical to be deployed in extreme temperature conditions.

Development and evaluation of nitrile rubbers seals for power transformer application

Mineral insulating oil (MIO) and natural ester insulating (NEI) oil are used in power transformers as an insulating fluid, while elastomeric seals are usually composed of nitrile rubber (NBR). The proprieties of these seals can change in contact with insulating oil. Variation in sealant properties is undesirable in power transformers. In this work, the variation of some elastomer properties was evaluated before and after accelerated aging in MIO and NEI. The developed elastomeric compositions showed variation in the stress and strain at break after the aging test. It also appeared that MIO penetrated the samples and that dioctylphthalate (DOP) migrated or was extracted into MIO and NEI. The samples vulcanized with peroxide showed better results than those vulcanized with sulfur.

Experimental and molecular level analysis of natural ester delaying degradation of cellulose insulation polymer

Developing green insulation materials has become an important direction for future research. As a new environmental insulation liquid, natural ester can effectively delay cellulose insulation polymer ageing. Mastering the mechanism of natural ester delaying the cellulose ageing could promote its application in power transformers. In this study, based on the accelerated thermal ageing of pressboard immersed in natural ester and 25# mineral oil at 120°C for 221 days, the thermal ageing rate and the levelling off degree of polymerisation (LODP) for two kinds of oil-impregnated pressboards were compared. The molecular level mechanism of natural ester delaying cellulose degradation and keeping higher LODP value was proposed using molecular dynamics simulation. At the early stage of thermal ageing, cellulose with a higher degree of polymerisation (DP) can form many hydrogen bonds with hydronium ions, and their binding energy is stronger, which can accelerate the acid hydrolysis of cellulose, causing the DP of pressboard immersed in natural ester and mineral oil to decrease rapidly. With the breaking of the cellulose molecular chain, the number of hydrogen bonds and binding energy between cellulose and hydronium ions becomes smaller and the thermal ageing rate decreases gradually. At the end stage of ageing, it is difficult for the hydronium ions to enter the crystalline cellulose, acid hydrolysis of crystalline cellulose is hard to conduct, leading to the occurrence of the LODP phenomenon. The degradation rate of cellulose in natural ester is only 50% of that in mineral oil. The cellulose LODP value in natural ester is over 200 larger than that in mineral oil. Compared with the mineral oil-cellulose system, natural ester can form hydrogen bonds with hydronium ions and lead to fewer hydronium ions in cellulose, fewer hydrogen bonds and smaller binding energy between cellulose and hydronium ions, which can reduce the acid hydrolysis reaction of cellulose. This study provides a theoretical explanation for natural esters to delay the ageing of insulation paper.

Assessing the dielectric performance of Sclerocarya birrea (Marula oil) and mineral oil for eco-friendly power transformer applications

The ever increasing power demand has forced the power sector companies to increase their generation, transmission and distribution in turn increasing the number of power transformers in the system where necessary. Depending on the nature of operations, the transformers are chosen as either dry-type or liquid-cooled and the preference is mostly liquid cooled. Naphthenic oils have been the primary choice over the years and alternative solutions in the form of natural esters are researched extensively due to the environmental effects of Mineral Oil (MO). One such ester, Marula is presented in this research. The experiment places its focus on measurement of electrical, physical, chemical and thermal characteristics as per the standards of ASTM and IEC. The results prove the superior dielectric performance of MAO over MO. The antioxidant rich MAO exhibits superior dielectric properties and restores faster than MO after the instances of breakdown phenomena. The antioxidants show stability at both the low and high temperatures, and temperature causes minimum damage to antioxidants. In addition to that the use of such dielectric coolant minimizes the winding damage inside the transformer tank. Thus, it can be said that MAO is an excellent coolant and improves the efficiency of the transformer without the requirements of additional cooling devices.

Experimental studies on the influence of benzyl benzoate on viscosity of vegetable oil based insulating liquids for power transformer

For insulating liquids in power transformers, the development of low viscous vegetable oil based liquids has been proposed in this work. The viscosity reduction of vegetable oil based liquids has been achieved by processing of the natural esters with different levels of concentration of aromatic solvent of benzyl benzoate. Two categories of vegetable oil based liquids, namely edible such as sunflower oil, palm oil and sesame oil, and non edible such as honge oil, neem oil and punna oil are considered for this investigation. The analysis is also extended to investigate the influence of benzyl benzoate on other critical properties of vegetable oil based liquids such as breakdown voltage, flash point, moisture content, acidity, and density. From the experimental results, it is revealed that inclusion of benzyl benzoate has shown considerable reduction in viscosity of vegetable oil based liquids. Also based on properties of processed natural esters, results have given away the positive encouragement towards the development of low viscous insulating liquids with combined benzyl benzoate and natural esters for application in high voltage power transformers.

Investigation of Survival/Hazard Rate of Natural Ester Treated with Al2O3 Nanoparticle for Power Transformer Liquid Dielectric

Increasing usage of petroleum-based insulating oils in electrical apparatus has led to increase in pollution and, at the same time, the oils adversely affect the life of electrical apparatus. This increases the demand of Mineral Oil (MO), which is on the verge of extinction and leads to conducting tests on natural esters. This work discusses dielectric endurance of Marula Oil (MRO), a natural ester modified using Conductive Nano Particle (CNP) to replace petroleum-based dielectric oils for power transformer applications. The Al2O3 is a CNP that has a melting point of 2072 °C and a low charge relaxation time that allows time to quench free electrons during electrical discharge. Al2O3 is blended with the MRO and Mineral Oil (MO) in different concentrations. The measured dielectric properties are transformed into mathematical equations using the Lagrange interpolation polynomial functions and compared with the predicted values either using Gaussian or Fourier distribution functions. Addition of Al2O3 indicates that 0.75 g/L in MRO has an 80% survival rate and 20% hazard rate compared to MO which has 50% survival rate and 50% hazard rate. Considering the measured or interpolated values and the predicted values, they are used to identify the MRO and MO’s optimum concentration produces better results. The test result confirms the enhancement of the breakdown voltage up to 64%, kinematic viscosity is lowered by up to 40% at 110 °C, and flash/fire points of MRO after Al2O3 treatment enhanced to 14% and 23%. Hence the endurance of Al2O3 in MRO proves to be effective against electrical, physical and thermal stress.

Impact of ultrasonic treatment process on pour point of vegetable oils based liquid insulation

This study presents an application of ultrasonic technology in the high voltage liquid insulation domain towards the reduction of pour point of vegetable oil samples for the utilization of vegetable oils as liquid insulation in cold climate areas on power transformers. Pour point reduction has been achieved by processing the vegetable oil samples by using ultrasonic treatment process with 100 W and 30 kHz ultrasonic waves for various exposure times of 15, 30, 45 and 60 min. Edible vegetable oils such as sunflower oil, palm oil, sesame oil and non edible vegetable oils such as honge oil, neem oil and punna oil are considered as two categories of vegetable oils for this experimental investigation. Ultrasonic treatment process results in the reduction of pour point of vegetable oils to meet out the standard value of pour point for liquid insulation as per IEEE Standard C57.147, 2018. A significant reduction in pour point temperature of vegetable oil samples have been obtained with an increased exposure time. The obtained variations in pour point after exposure with ultrasonic waves may be due to the possible changes in crystallization kinetics of fatty acids components of vegetable oil samples due to energy input of ultrasonic waves. The experimental results have given a way towards the positive encouragement and development with ultrasonic treatment for achieving low pour point vegetable oils as liquid insulation in power transformers for applications on cold climatic areas.

Influence of electrical and thermal ageing on the mineral insulating oil performance for power transformer applications

In the present work, a new electrothermal combined stress test cell has been designed and fabricated to conduct accelerated electrothermal ageing. The fabricated test cell includes all possible real working conditions of the transformers. The effects of accelerated electrothermal ageing on the performance of power transformers with thermally upgraded Kraft (TUK), Nomex-910 and Nomex-410 solid dielectrics in conjunction with mineral oil have been investigated. The accelerated electrothermal ageing has been performed for a temperature range of 100°C to 220°C, along with 10 kV electrical stress. Subsequently, several electrical, thermal, mechanical and chemical properties of transformer oil and different paper dielectrics have been determined. It has been observed from the diagnostic test results that Nomex impregnated mineral oil samples have better electrothermal performance as well as oxidation stability when compared to the thermally upgraded Kraft oil samples. Therefore, Nomex insulating materials in conjunction with mineral oil are suggested as alternative solid dielectrics for power transformers in order to achieve better oxidation stability, improved thermal performance for long service runs and reduced operating and maintenance costs. It is envisioned that the present experimental study will be very beneficial to utility managers and end-users of power transformers.

Comparison of Ageing Characteristics of Superior Insulating Fluids With Mineral Oil for Power Transformer Application

Natural Esters (NEs) with a high proportion of Unsaturated Fatty Acids (UFAs) were used in this research. A Superior Insulating Fluid (SIF) is prepared by blending NEs like Baobab Oil (BAO) and Mongongo Oil (MGO) with a pure dielectric like Kerosene (KER) and subjected to ultrasonic wave treatment at 30 kHz . Then, accelerated heating of SIF is carried out in the presence of Kraft Paper (KP) and Copper Plate (CP) for 10 hours a day at 90 ° C for 30 successive days. The deterioration of the dielectric characteristics of SIF, KP, and CP was measured as per IEC and ASTM standards before and after the schemes of stressing. The failure rate of SIF, KP and CP was compared to understand the influence of KER in NEs. The KER addition at 5% proportion protects the oil from dielectric weakening, copper from ageing and likewise, the viscosity remains at the original level. The use of KER in NEs have thin the oils and protects the copper from oxidation, thus preserving the quality of oils for several years. The extrapolation of data is done using a polynomial function and for 90 days, where the selected SIFs show 7% of ageing rate when compared to MO that shows 50% ageing rate. This affirms that SIFs are a suitable substitute for Mineral Oil (MO) and reclamation SIFs are achieved using natural reclamation/filtration techniques using Activated Bentonite and Activated Carbon. Hence spilling and reusing the SIFs does not harm the environment as that of Mineral Oil (MO).

Static and Dynamic Evaluation of a Winding Deformation FBG Sensor for Power Transformer Applications.

Power transformer is the most important and expensive equipment used in the electric power industry. Fiber Bragg grating (FBG) sensors has stood out as a flexible and particularly suitable tool for power transformer monitoring being a passive and dielectric sensor element. In this work we evaluated the performance of FBG pressure sensors developed to monitor the static and dynamic pressure in high voltage winding transformers during events such as short-circuit and inrush current. Two types of sensors packaging materials were evaluated in laboratory: polyether ether ketone (PEEK) and transformerboard (TB). The sensors have been tested for high intensity and short duration impacts similar to those occurring in short circuits. In addition, we evaluated the time response of sensors using an interrogation system with a 5 kHz sweep in order to analyze the short circuit response time properly. The results pointed that FBG pressure sensors using PEEK and TB are suitable for transformer winding monitoring. The static sensitivity obtained to PEEK based sensors was 0.911 pm/N, in the range of 800 N to 1500 N. This sensitivity is 4.47 higher than TB based sensors sensitivity. Dynamical tests performance showed an excellent repeatability for both sensors, in agreement with static observation.