Power Transformer Insulation Research Articles

Reliable Assessment of Oil-Paper Insulation Used in Power Transformer Using Concise Dielectric Response Measurement

Oil-impregnated paper is usually the preferred choice of insulation in power transformers. The working life of any transformer depends on its insulation condition. The paper conductivity, moisture content and dissipation factor of solid insulation are a few crucial parameters used to determine the insulation condition. The reliable estimation of such parameters for diagnosis of solid insulation requires a complete profile of polarization current which is time-consuming. Hence, utilities always prefer non-invasive and rapid techniques to predict insulation conditions and minimize shutdown time. The proposed technique is based on a short-duration polarization current data. The present manuscript suggested a method that uses the initial decay rate of recorded polarization current data to predict various performance parameters related to paper insulation. In order to show the effectiveness of the proposed method, the analysis is performed on the data measured from various in-situ transformers.

Investigation of high-voltage discharge in oil on a simulator with a different set of defects

Background: The article describes a device for simulating various insulation defects for use with acoustic control devices for power transformers included in the power supply system of railway transport. The parameters of the recorded signals of the simulator are given, which will make it possible to recognize various insulation defects when diagnosing power transformers under operating conditions which will help to avoid emergency modes and interruptions in the operation of the electric rolling stock of railways.
 Aim: experimental studies of a simulator with a different set of defects, obtaining the values of the parameters of acoustic control signals for various defects in the insulation of power transformers.
 Methods: experimental studies of automated means of acoustic control, development of technical means for simulating various defects in the insulation of power transformers, processing of acoustic control signals.
 Results: the block diagram of the simulator with a different set of defects is given, the values of the parameters of acoustic monitoring signals for various defects in the insulation of power transformers are given.
 Conclusion: the above device allows you to reproduce various defects in the insulation of power transformers, to recognize such defects according to the proposed parameters of acoustic control signals.

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.

Performance Assessment of Cellulose Paper Impregnated in Nanofluid for Power Transformer Insulation Application: A Review

Insulation cellulose paper is a basic measure for a power transformer’s remaining useful life, and its advantageous low cost, electrical, and mechanical properties have made it an extensive insulation system when impregnated in a dielectric liquid. Cellulose paper deteriorates as a result of ageing due to some chemical reactions like pyrolysis (heat), hydrolysis (moisture), and oxidation (oxygen) that affects its degree of polymerization. The condition analysis of cellulose paper has been a major concern since the collection of paper samples from an operational power transformer is almost impossible. However, some chemicals generated during cellulose paper deterioration, which were dissolved in dielectric liquid, have been used alternatively for this purpose as they show a direct correlation with the paper’s degree of polymerization. Furthermore, online and non-destructive measurement of the degree of polymerization by optical sensors has been proposed recently but is yet to be available in the market and is yet generally acceptable. In mitigating the magnitude of paper deterioration, some ageing assessments have been proposed. Furthermore, researchers have successfully enhanced the insulating performance of oil-impregnated insulation paper by the addition of various types of nanoparticles. This study reviews the ageing assessment of oil-paper composite insulation and the effect of nanoparticles on tensile strength and electrical properties of oil-impregnated paper insulation. It includes not only significant tutorial elements but also some analyses, which open the door for further research on the topic.

Review on monitoring of transformer insulation oil using optical fiber sensors

Power transformers are critical components of power system networks. Failure of this equipment risks the entire system, resulting in power outages and income losses. The reliability of this device is generally determined by its insulating quality. Hence, it is essential to check the transformer's insulation oil condition regularly. Traditional test techniques for assessing the condition of power transformers insulation oil have several drawbacks. Optical fiber-based sensors for monitoring transformer oil conditions have been designed to address such issues. This paper presents a brief review of optical fiber sensors for measuring oil level, oil aging assessment, moisture content and temperature in transformer oil. This review shall be of benefit to both engineers and researchers who are doing research in this field.

Development of nominal rules on the Fuzzy Sugeno method to determine the quality of power transformer insulation oil using Dissolved Gas Analysis data

This paper aims to develop the nominal rules on the Fuzzy Logic Method using the Sugeno-Fuzzy Inference System (FIS) for Dissolved Gas Analysis (DGA) and determine the quality of the power Transformer 1 and Transformer 6 insulating oil at the Buduran 150 kV substation. The nominal number of proposed fuzzy rules is 1920 rules. Implementing the Fuzzy-Sugeno method on Transformers 1 and 6 shows that the six input variables from the DGA test can produce a Total Dissolved Combustible Gas (TDCG) output value of 32.67 and 26.19 ppm, respectively. Both values indicate that the insulating oil of Transformers 1 and 6 are in condition one and, at the same time, indicates that the dissolved gas composition is in Normal status. Furthermore, the TDCG value, condition, and quality status of the insulating oil have the same or 100 % accuracy compared to the DGA test by PLN (UPT Surabaya). Thus, the nominal development of fuzzy rules using the Fuzzy-Sugeno method can perform DGA analysis more accurately to determine the quality of power transformer insulation oil compared to previous studies.

Performance Analysis of Blended Neem and Olive Oil as Alternate Liquid Insulation for Power Transformers

Performance Analysis of Blended Neem and Olive Oil as Alternate Liquid Insulation for Power Transformers

Importance of Depolarization Current in the Diagnosis of Oil-Paper Insulation of Power Transformer

Importance of Depolarization Current in the Diagnosis of Oil-Paper Insulation of Power Transformer

Plasma Dynamics-Based Modeling and Analysis of Partial Discharge in Voids Inside Insulation of Power Transformer

Partial discharge (PD) modeling in voids is being studied; earlier, however, most studies considered a simplified model with many adjustable parameters. In this article, a comprehensive comparative study is being done with possible void shapes in transformer insulation using a modified drift-diffusion model with single adjustable free parameter of the electron generation rate and considering the secondary ionization process. In simulation studies, plasma-dynamics-based models are used to better understand PD activity inside voids. A drift-diffusion model is used for investigating the PD phenomena inside air-filled voids of commonly found geometries, namely, cylindrical, spherical, and ellipsoidal, bounded by different insulating materials in power transformers. The model is applicable for all void shapes and material of insulation. PD inception field, residual field, space charge density, and other electrical properties are obtained, and all the possible parameters are incorporated in the model thus improving its accuracy. In this article, the effect of void shape and insulation material on the PD activity is obtained. The inception electric field at which the discharge initiates is found to be lowest in case of spherical void resulting in easy formation of plasma discharge. This study thus uncovers the physical mechanism of PD inside insulation thus helping in maintenance and optimum design of transformer insulation.

The Method for Improving the Effect of Oil-Replacement on Aging Assessment of Power Transformers Insulation Based on Methanol

The Method for Improving the Effect of Oil-Replacement on Aging Assessment of Power Transformers Insulation Based on Methanol

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.

Major Defects and Diagnostics of Solid Insulation of Power Transformers

Major Defects and Diagnostics of Solid Insulation of Power Transformers

Research on the Influence of Moisture Exchange between Oil and Cellulose on the Electrical Parameters of the Insulating Oil in Power Transformers

The article presents an oil moistening method, identical to the oil moistening in power transformers. Moistening took place through the migration of moisture from the moistened pressboard to the brand new oil. The AC electrical parameters (admittance, phase shift angle, permittivity, loss tangent and conductivity) of the brand new and moistened insulating oil were tested. All measured parameters were found to be affected by the oil moistening. The greatest changes were observed in the loss tangent and conductivity. Moisturization increases the value of tanδ at a frequency of 10−4 Hz from about 20 to about 70. With an increase in frequency to about 400–1000 Hz, a minimum is observed, the position of which depends on the temperature. Its value for moistened oil is about six times lower than for brand new oil. This moisturizing increased the activation energy of the conductivity from 0.466 ± 0.0265 eV to 0.890 ± 0.0115 eV. This is likely due to the acceleration of water molecules diffusion from the pressboard into the oil with increasing temperatures. The observed changes in the oil parameters caused by moistening should be taken into account while analyzing the power transformers insulation condition using the FDS method.

Prediction Model of Bubble Formation in Oil-Paper Insulation Based on the ITBE Envelope

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

Partial Discharge Detection and Sensitivity Improvement for Bushing Based on Optical Interference Technique

Bushing plays a significant role in insulation and mechanical support for power transformers. Its working state is closely related to the reliable operation of power transformers. To overcome the electromagnetic interference and security risks during sensor installation, a Sagnac interference optical technique for partial discharge (PD) detection is proposed in this paper. By establishing a simulation model of the sensing structure, it is verified that output signal amplitude varies periodically with the length of sensing and delay fibers. Moreover, the output value decreases with increasing probe radius. The results show that a delay fiber of 1.5 km, a sensing fiber of 3 m, and a bending radius of 5 mm are optimal parameter combinations to detect PD in a 72.5 kV defective bushing. In addition, consistent detection waveforms induced by both internal and external defects are obtained by the optical sensor and high frequency current transformer (HFCT) simultaneously, then the effectiveness of the optical sensor on detecting PD signals for bushing is verified. It is of great help to carry out online monitoring of bushing insulation defects through optical non-destructive installation.

Life Span Assessment of the Insulation for Power Transformers: A Review

A power transformer is a vital link for any electrical transmission and distribution network, used to raise the voltage levels of the generators, and transformers at local substations to supply loads. However, an unexpected failure of power transformers cause an electricity shortage to the consumer, involve the loss of millions of dollars for utility companies, industrial failure costs, environmental hazard costs due to oil spillage and also indirectly to the national security. Hence, predicting the lifespan of a power transformer has been considered an important issue for energy companies in order to reduce the transformer failure. Power transformers that reach the end of its life usually do so unexpectedly, causing power reliability problems, which cost a lot of money. Therefore, knowing the factors that play part in the degrading process of a power transformer could help power companies determine how long a power transformer have before breaking down and allow them to perform any necessary action before the power transformer starts giving problems. This research paper therefore focuses on the life assessment of the insulation for power transformers. In this paper, different approaches used for the evaluation of lifespan of power transformers were reviewed. These approaches have become powerful tools to overcome the problem of transformer failure and aging, because these tests are carried out more frequently by utilities. This research paper therefore, will help utilities to monitor the major parameters, to determine the remaining life and the lifespan of power transformers. Keywords: Power Transformers, Electrical Transmission Network, Electrical Distribution Network, Lifespan, Consumers, Transformer Failure, Reliability, Transformer Aging. DOI: 10.7176/JETP/12-3-02 Publication date: August 31 st 2022

Eco-Friendly Ester Fluid for Power Transformers versus Mineral Oil: Design Considerations

Mineral oil has long been used as an adequate coolant and dielectric medium in power transformer design. However, it is flammable and environmentally risky as it may be leaked or spilled. Therefore, ester fluids, which have been increasingly used in the last two decades, look promising as an ideal dielectric option. This research aims to better understand how using ester fluid insulation in power transformers impacts their physical and electrical dimensions, including their load-losses, impedance, masses, and equipment dimensions. Three case studies were carried out in a Portuguese electrical equipment manufacturer’s facility, with varying electrical parameters and physical properties of the mineral oil and ester-filled power transformers. The main results enhanced the known good electrical behavior of ester fluids, namely creating a lower electric field around winding wedges, yet the use of ester fluids led to higher load-losses, larger masses, additional radiators and, consequently, higher manufacturing costs. Nevertheless, the contribution of ester-filled power transformers to the improved environmental safety (reducing spillage and fire risks), among other advantages, makes ester fluids a truly eco-friendly option for power transformer design.

Checking of the condition of transformers and the efficiency of oil regeneration with RVM (return voltage measurement)

Up to now the insulation in HV power transformers has been made from oil/paper therefore the diagnosis of this kind of insulation will be also important in the next forty-fifty years. The lifetime of this equipment strongly depends on the condition of the insulation system. The ageing process of oil/paper insulating systems is a very complex and complicated phenomenon. In order to get a well-supported decision on the further operation of aged transformers, relevant information would be necessary on the condition of the oil-paper insulation. We also know that the oil-paper insulation has almost always inhomogeneous condition considering the temperature, moistening and ageing processes. The classical methods (insulation resistance, loss tangent, etc.) characterise the insulation by single measured value. This single value is not sufficient for relevant characterisation and diagnosis of such a complex system with lots of tons of insulation and with almost always inhomogeneous distribution of temperature, moisture and ageing product. If we measure the polarization spectra in three states (new insulation in equilibrium and uniform polarization spectrum, new insulation with not uniform distribution of polarization spectrum, later reaching again the uniform distributions) the shape of three polarization spectra will be different. Comparing the polarization and classical methods of this three case we can realize that sometimes the “classical single values” are almost the same but the polarization spectra are different. The three response methods provide very practical information about the insulation system (e.g. moisture, ageing). The moistening and accumulation of ageing by-products change the distribution of interfacial polarisation in the range of long time-constants. These promising response methods measure the polarisation distribution in the range of long time-constant (with other words, in the low frequency range). The three test methods were: Return Voltage measurement (RVM), the C and tgδ measurement in range of some tens of mHz to 50 Hz (FDS=Frequency Domain Spectroscopy), and the measurement of DC charging and discharging currents (PDC=polarisation and depolarization currents) up to some thousands of sec. These equivalent methods (RVM, FDS and PDC) are able to follow the changing of condition of insulation contrary to classical methods. Therefore a little bit surprising that until now the convenient standards is missing considering the polarization methods. In an earlier Hungarian research work (Budapest University of Technology) almost all the necessary measurements have been realized, consequently we are in possession of fundamental data considering the polarization methods. This paper would like to show a short review about the RVM technique, the correct interpretation of RVM data and a case study for the checking of the efficiency of the oil reclamation with RVM technique.

Intelligent Expert System for Diagnosing Faults and Assessing Quality of Power Transformer Insulation Oil by DGA Method

Accurate assessment of oil and fault diagnostics of electrical power transformer insulation for lifelong endurance are the key issues addressed in this research. The durability of a transformer is significantly determined by the quality of its insulation oil, which deteriorates over time due to temperature fluctuations and moisture content. Protecting transformers from potential failure through the early and precise diagnosis of faults and efficient assessment of oil quality during the actual conduct of the operation can avoid sizeable economic losses. The ANFIS Expert System that uses intelligent software plays an important role. The dissolved gas analysis (DGA) in oil is reliable for diagnosing faults and assessing insulation oil quality in transformers. Transformer power plant protection teams often suffer sudden breakdowns that lead to massive damage and huge financial losses. The oil in transformers must be appropriately treated to circumvent such failures. In this research, an ANFIS Expert System was used to diagnose faults and assess insulation oil status and quality in power transformers. by the Rogers ratio method depending on the DGA in oil, a suitable treatment was identified. The graphical user interface from the MATLAB environment was used and proven effective for fault diagnosis and oil quality evaluation. The training algorithm can assess oil quality according to the specifications of the IEEE standard C57-104 and the IEC standard 60599.

Diagnostics of power transformers operating for many years in the power supply system through gases in the composition of transformer oil

Oiled power transformers and autotransformers 40-60 years ago are still in operation in Uzbekistan. At the same time, diagnostic methods for determining faults in transformers and autotransformers remained the same. This article partially analyzes the factors affecting the oils of power transformers and autotransformers used in the agricultural sector. It is known that transformer oil performs the functions of cooling and insulation. During use, the oil is in direct contact with air through the respiratory system. There is a process of transition of moisture and various gases in the composition of the air into the composition of the oil. By the composition of gases, it is possible to determine the reasons for the deterioration in the quality of the main and additional insulation of oil-immersed power transformers. The issues of influence on the state of insulation of marsh gases appearing inside (at the bottom) of the tank of oil transformers and partial discharges in oil-gas medium have been little studied.