Paper Insulation System Research Articles

Pengembangan Uji Eksperimental Penuaan Dipercepat Sistem Isolasi Kertas Terendam Minyak Transformator

A transformer is a static electric device that is used to change the alternating voltage to a higher or lower level and is used to transfer energy from one electric circuit to another without changing the frequency. When the transformer is working, there is a temperature rise in the transformer which affects the degradation of the insulating paper and transformer oil. This accelerated aging tester applies the drying and vacuuming process as well as the arrangement of paper insulation racks to achieve maximum test results. The research method refers to IEC 60216-3 2006 for aging time, IEC TS 62332-1 2014 and IEC TS 62332-1 2011 as a reference for the Development of Accelerated Aging Experimental Test Cells for Transformer Oil-immersed Paper Insulation Systems. After achieving the existing goals, the addition of the drying process resulted in quite good Breakdown Voltage test results, not only that after the addition of vacuum it produced a good oil color according to ASTM D1500 as well as after the presence of paper placement racks the results of good tensile strength testing were proven by a graph which relatively decreased from sample 1 to sample 3.

Multiple Sulfur Corrosion Simulation on the Oil–Paper Insulation System Under Synergistic Electric and Thermal Fields

Sulfur corrosion in transformers results in insulation deterioration failures. Therefore, in this study, multiple sulfur corrosion was simulated on the oil–paper insulation system. The mechanical properties and hydrogen bond of the insulating paper as well as the mean square displacement and shear viscosity of the insulating oil were investigated under different combinations of electric and thermal fields. The electric field could promote the degradation of the elastic modulus of cellulose. The influence of the AC electric field on the modulus is not as obvious as that of the DC electric field. Temperature has a significant effect on the modulus parameters. With the increase in the temperature, the elastic modulus decreases considerably. The radial distribution function of the model was also investigated. Cellulose can easily form intramolecular hydrogen bonds under AC electric fields. Furthermore, intermolecular hydrogen bonds are easily formed under a DC electric field. The shear viscosity of insulating oil decreases with the increase in the temperature. The presence of the electric field could increase shear viscosity. The results of the study can provide some reference for the microscopic mechanism of multiple corrosive sulfides and investigate effective protection techniques against sulfur corrosion.

Water Content in Transformer Insulation System: A Review on the Detection and Quantification Methods

Water can be an irritant to a power transformer, as it is recognized as a major hazard to the operation of transformers. The water content of a transformer insulation system comprises the water in the transformer insulation oil and in the cellulose paper. The increase in the water content in the insulation system leads to reduced breakdown voltage, accelerated aging of the oil–paper insulation system, and the possibility of producing bubbles at high temperatures. Therefore, various techniques have been applied to measure the water content in both oil and paper insulation. This article comprehensively reviews and analyzes the methods (technically or nontechnically) that have been used to monitor the water content in transformer insulation systems. Apart from discussing the advantages and major drawbacks of these methods, the accuracy, measurement time, and cost of each technique are also elucidated in this review. This review can be extremely useful to the utility in monitoring and maintaining the good condition of transformers. Based on the reviewed methods and their challenges, a few future research directions and prospects for determining the water content in transformer insulation systems are outlined, such as utilizing artificial intelligence and enhancing current techniques.

Gas production mechanism of Irgamet 39 and its long‐term corrosion resistance

AbstractThe phenomenon of transformer failure caused by oil‐sulphur corrosion of oil₋paper insulation system has always been concerned by scholars. Irgamet 39 is the most used metal passivator for inhibiting sulphur corrosion. However, Irgamet 39 causes abnormal dissolved gas in oil during the process of exerting anti‐corrosion effect. Herein, the gas production mechanism of Irgamet 39 and its long‐term corrosion resistance were investigated. Compared with other metal passivators, the Irgamet 39 produces more dissolved gases in oil, especially H2, CO and CO2. The main sources of free radicals in the gas production process are from the branched chains of the Irgamet 39 structure (−CH2N(C8H17)2 and −CH3). Furthermore, the ageing products of insulating paper and oil promote the cleavage of the chain in the Irgamet 39 molecule, which then causes Irgamet 39 to generate more dissolved gases. Irgamet 39 exhibits excellent long‐term corrosion inhibition properties,while it also leads to abnormal gases in the oil, which can affect the interpretation of the dissolved gas analysis data and thus interfere with the diagnosis. This work provides useful information for the practical application of Irgamet 39 and helps electrical workers make reasonable predictions for transformer problems.

Effect of Electrical Accelerated Aging on DC Resistivity of Mineral Oil Used in Power Transformers

Power transformers are still equipment of primary importance within power grids. The recent paradigm changes registered in the field of energy require the interconnection of electrical grids of much larger areas, even up to the level of an entire continent. In this context, knowing the state of the electrical equipment and that of the power transformers is an essential aspect to ensure safe operation conditions. The present work is related to the vulnerability of the oil–paper insulation systems of power transformers to different aging factors and their quick degradation under certain conditions. In this regard, the study proposed in this paper considers the measurement of DC resistivity on mineral oil samples contaminated with small amounts of accelerated aging oil under the action of high-strength electric field and partial discharges. In the absence of standardized procedures for accelerated electrical aging of mineral oil, an original method presented and discussed in previous articles is used. The obtained results clearly indicate that under the action of electrical stress, the mineral oil resistivity decreases significantly, showing that the oil’s electric properties worsen.

Research on influence factors of micro-bubbles generation mechanism in oil paper insulation of 1000 kV transformers

The 1000 kV transformer is one of the most important equipment in ultra high voltage (UHV) power grid, and its service life largely depends on the state of its oil paper insulation system. Especially when micro-bubbles appear in oil paper insulation, the insulation performance of oil paper insulation will be greatly reduced. In this paper, the oil paper insulation micro-bubbles generation platform has been built in the laboratory for 1000 kV transformers. Based on the platform, the influence of temperature rate on oil paper insulation micro-bubbles was studied firstly. By setting the heating power, the micro-bubbles generation experiment of oil paper insulation samples with 3.0% water content was carried out. It is found that with the increase of heating rate, the initial temperature of micro-bubbles generation will increase and the time interval of micro-bubbles escape will be shorten. Then, the oil paper insulation samples aged for 0 day, 20 days and 40 days were tested. It is found that the longer the thermal aging time, the higher the micro-bubbles begin temperature, which directly shows that thermal aging could inhibit the generation of micro-bubbles. In addition, it is found that different layers of insulation paper also have an effect on the generation of micro-bubbles. These results can provide theoretical data support for the operation load setting and fault diagnosis of 1000 kV transformers.

Correlation Analysis and Regression Fitting of Multiple Sulfide Aging Characteristic Parameters

The corrosion of transformers by multiple sulfides seriously affects the safe operation of transformers. However, there is a lack of quantitative characterization of the extent to which temperature and oxygen as well as changes in sulfide species affect the aging of oil–paper insulation. In this study, the aging characteristics of oil–paper insulation systems were analyzed in terms of the moisture in the oil, moisture in the paper, acid value, and furfural in the presence of multiple sulfides, where the temperature and the oxygen concentration are used as independent variables. A strong positive correlation between the acid value and the furfural obtained by means of Spearman’s correlation analysis. The acid value and furfural content in the oil were then analyzed and compared according to a nonparametric test, and it was found that both the oxygen changes and the temperature changes had a relatively obvious effect on the acid value in the oil. The effect of the temperature change on the furfural was greater than the effect of the oxygen change on the furfural. Finally, a multiple linear regression analysis was performed for the change in the acid value of the oil with the change in the oxygen content and temperature to obtain the linear fitting formulas for the effects of the time, temperature, oxygen content percentage, and sulfide groups on the acid value. This study can be used to quantify the magnitude of the influences of the oxygen, temperature sulfide groups, and other factors on the aging characteristic parameters of the oil–paper insulation system and to provide a certain reference for studying the quantitative characterization of the sulfur corrosion degree by using the change in the acid value in oil.

Partial Discharge Characteristics and Deterioration Mechanisms of Bubble-Containing Oil-Impregnated Paper

Bubbles, as typical defects of oil–paper insulation systems, pose a great threat to the insulation state. In this article, the characteristics and mechanisms of the partial discharge (PD) inception, evolution, and induced breakdown of bubbles embedded between oil-impregnated paper (OIP) layers are investigated. The results show that the PD inception has a significant statistical time delay due to the lack of free electrons. The PD inception time delay (PDTD) follows an exponential distribution and leads to the large dispersion of the PD inception voltage (PDIV), which follows a Weibull distribution. The changes in PD behavior [charge, repetition rate, pulse current waveform, and phase-resolved PD (PRPD)] over time all show two separable stages (stages 1 and 2). The continuous recording of bubble area and gas composition under PD reveals that the evolution of bubble PD is attributed to the change in gas composition rather than the change in surface conditions as believed by researchers. The OIP breakdown induced by bubble PD indicates two breakdown modes, fast and slow, which correspond to direct-induced breakdown in stage 1 and cumulative-damage breakdown in stage 2. The former occurs because of the severe distortion of the electric field by the space charge at the head of the discharge channel inside the bubble, whereas the latter occurs because of the gradual deterioration of the OIP due to the continuous PD action. This study increases our understanding of the mechanisms of bubble discharge and of oil–paper insulation deterioration, and it provides guidance for fault diagnoses.

Description of space charge transport in oil‐paper insulation using adaptive time‐stepping transient upstream finite element method

The charge transport and accumulation in oil–paper can cause the insulation degradation. So far, the most widely used model to simulate space charge transport and accumulation is the bipolar charge transport (BCT) model, which can well simulate the space charge dynamics. However, there are two shortcomings in the algorithms for solving the BCT model. One is that there is almost no use of vectorisation technology, which may increase the complexity of the algorithm, the other is the usage of fixed step size which might bring extra computation cost. In view of this, an adaptive time-stepping transient upstream finite element method (FEM) is developed to solve the BCT model considering trapping/detrapping, as well as the recombination phenomenon under DC condition in this article. Then, a vectorisation technology is used in the method to optimise the algorithm. Moreover, the adaptive time-stepping method is introduced in simulation to reduce computation time and calculation amount. Simulation results are obtained by programing and later presented, which are basically consistent with the corresponding experimental results. Therefore, the proposed method is expected to promote the optimization design of the oil–paper insulation system.

Insulating Paper Cellulose with High Mechanical Performance and Low Polarizability: The Effect of Doping Concentration on Polyhedral Oligomeric Silsesquioxanes‐Modified Cellulose

To study the effect of doping concentration on polyhedral oligomeric silsesquioxane (POSS)‐modified cellulose and its internal mechanism, molecular dynamics is used to establish a pure cellulose model and 1, 2, 3, 4, and 5 wt% POSS‐modified cellulose models, and the cohesive energy density and solubility parameter, mechanical properties, free volume, mean square displacement, and polarizability are calculated at 343 K. The simulation results show that the addition of POSS effectively improves the compatibility and mechanical performance of cellulose and at the same time enhances its thermal stability. Among the five modified cellulose models, the modification effect of the 3 wt% POSS‐modified cellulose model is the best. It is also found that the addition of POSS effectively reduces the polarizability of cellulose and even the electric field distribution in the oil paper insulation system, so as to enhance the insulation of the transformer. With the increase in concentration, the polarizability decreases.

Decomposition Gases of Insulating Oil in Oil-impregnated Paper Insulation System with an Oil Gap

Decomposition Gases of Insulating Oil in Oil-impregnated Paper Insulation System with an Oil Gap

A modified XY model of transformer oil–paper insulation system including non‐uniform aging and conductance effect

A modified XY model of transformer oil–paper insulation system including non‐uniform aging and conductance effect

Overheating and discharge fault identification for novel three-element mixed oil–paper insulation system based on new characteristic gas combination parameters

To support the safe operation of the novel three-element mixed insulation oil (TEMO) transformer, gas generation behaviors of the TEMO oil–paper insulation system under overheating faults and discharge faults were investigated. Results show that that the content of H2 and C2H6 generated by TEMO–paper insulation system is much higher than that in conventional mineral oil (MO)–paper insulation system under different overheating temperatures. Under partial discharge fault, the content of H2 dissolved in oil changes distinctly, while the content of C2H2 also increases with the discharge time. Under surface flashover breakdown, AC breakdown and lightning impulse breakdown fault, the content of H2 and C2H2 changes greatly compared to other gases, while the concentration of total hydrocarbon gases in TEMO–paper insulation system is smaller than that in MO–paper insulating system after the same breakdown times. The diagnosis model of overheating and discharge faults for the TEMO–paper insulation system was proposed based on the oil dissolved gas analysis, while H2, C2H2 and C2H4 were chosen as the characteristic gases and the boundary settings were determined. The verified result for the low-temperature overheating, lightning impulse and surface flashover fault for the TEMO–paper insulation system presents that the new diagnosis model is effective.

A Method for Diagnosing the State of Insulation Paper in Traction Transformer Based on FDS Test and CS-DQ Algorithm

Traction transformer is vital equipment in high-speed railway. Insulation status decides its safety and reliability, and the frequency-domain dielectric spectrum (FDS) test is one of the most effective methods reflecting the changing of insulation status. For field applications, the following problems should be addressed: 1) how to obtain the result of paper insulation from the combined result of the oil–paper insulation system and 2) how to discriminate the defects of insulation paper between aging and damp. In this article, the first problem was transferred to a nonlinear equation set, and a cuckoo search algorithm optimized by the differential evolution algorithm and the quadratic interpolation (QI) method (CS-DQ algorithm) was proposed to solve it. Then, the insulation states were discriminated by establishing a multiclass least-squares support vector machine (LS-SVM) model, in which the CS-DQ algorithm was also used. Finally, a diagnostic approach for the insulation paper in the traction transformer was proposed. The results in the laboratory show that the pure result of insulation paper can be obtained, and the insulation states can be discriminated effectively by using the proposed approach. Meanwhile, the proposed CS-DQ algorithm has a better performance than the conventional CS algorithm. The results of field testing also verify the proposed approach.

Method for Rating and Analyzing the Combined Effects of Moisture and Temperature on the Oil–Paper Insulation System of Power Transformers by Means of Load Variations

This paper presents an innovative method devised to study some of the harmful effects of moisture on power transformers, considering the possible formation of bubbles and free water. Its novelty stems from the fact that it comprises: (a) a rating system from “A” to “E” and their respective recommended actions and (b) an analysis that involves varying the different levels of electrical loads applied to the equipment. The importance of this work is confirmed when power transformers are exposed to unfavorable conditions that can critically affect their insulation. To this end, a tool to study moisture was developed, which uses the finite difference method, based not only on the experience of experts/analysts but also on existing studies in the area and on the analysis of a database of actual field tests. The contribution of this work is an efficient method, implemented via a computational algorithm, which provides a technique for the real-time or offline rating of power transformers, helping maintenance teams to diagnose problems and decide whether or not to repair the equipment. The tool provided the satisfactory results, which are presented in a case study of a real transformer operating at the local electric utility company. These results were obtained by applying different levels of electrical loads, for which thermal simulations were performed.

Effects of AC Electrical Stress, Oil Pressure and Insulation Construction on Time Transition of Partial Discharge Characteristics on Oil-impregnated Paper Insulation System for Oil-filled Cables

Effects of AC Electrical Stress, Oil Pressure and Insulation Construction on Time Transition of Partial Discharge Characteristics on Oil-impregnated Paper Insulation System for Oil-filled Cables

Concentration of 5‐hydroxymethylfurfural produced by insulating paper in an oil–paper insulation system

The transformer is a core device of the power system, and it is generally considered that the aging of insulating paper is important to the transformer. The aging process of insulating paper is the degradation process of cellulose. If it can be detected regularly, the aging of oil–paper insulating systems can be monitored conveniently. 5‐hydroxymethylfurfural is an important chemical substance produced by cellulose decomposition. It has broad prospects because of its many advantages. The oil–paper insulation system was thermally aged at 80, 90, 100, and 110 °C to measure the concentration of 5‐hydroxymethylfurfural on insulating paper and in transformer oil. In this paper, the concentration of 5‐hydroxymethylfurfural is detected by high‐performance liquid chromatography. The linear correlation coefficient of this method can reach 0.99, and the minimum detected concentration can be reduced to 10 µg/l. Experiments show that the concentration of 5‐hydroxymethylfurfural increases with the aging time, and when degree of polymerization (DP) decreased, the concentration of 5‐hydroxymethylfurfural increased. The correlation coefficient is greater than 0.92, which shows that there is an experimental relationship between the concentration of 5‐hydroxymethylfurfural and DP. The parameters of regression curves are different at different temperatures, but in actual operation, the temperature is low and remains stable. Therefore, 5‐hydroxymethylfurfural is expected to be a new indicator of the aging degree of oil–paper insulation system. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Accelerated Charge Dissipation by Gas-Phase Fluorination on Nomex Paper

The surface charge and space charge accumulation in paper used in oil–paper insulation system may distort electric field distribution and lead to the flashover and breakdown of insulation system. In this paper, the effect of gas-phase fluorination on the surface charge and space charge characteristics of oil-impregnated Nomex paper was investigated. Nomex T410 was fluorinated at 25 °C using F2/N2 mixtures with 20% F2 in volume at 0.05 MPa for 15, 30 and 45 min. Fourier Transform Infrared Spectroscopy (FTIR) proved that the molecular chain scission and cleavage occurred during gas-phase fluorination. Furthermore, the surface charge and space charge characteristic of the original and fluorinated oil-impregnated paper were measured using an electrostatic voltmeter and Pulsed Electroacoustic (PEA) equipment respectively. Furthermore, the hole and electron trap distribution of the samples were obtained by Isothermal Surface Potential Decay (ISPD) model. The results showed that both the positive and negative charge decay rates were accelerated by gas-phase fluorination and the hole, electron trap energy and density of the fluorinated samples were reduced by fluorination. It is suggested that the space charge dissipation was also accelerated by fluorination, indicating that gas-phase fluorination is an effective approach to modify the charge dynamics of oil-impregnated Nomex paper.

Semi-simultaneous Observation of Partial Discharges Signal, Light Emission and Bubbles, and Detection of Dissolved Gasses in Oil Gap on Oil Impregnated Paper Insulation System

Semi-simultaneous Observation of Partial Discharges Signal, Light Emission and Bubbles, and Detection of Dissolved Gasses in Oil Gap on Oil Impregnated Paper Insulation System

Method for predicting the remaining life of oil–paper insulation system based on stochastic degradation process

The service life of a transformer depends on the ageing degree of the internal oil–paper insulation. In order to reliably predict the remaining service life of oil–paper insulation for a single transformer, this study proposes a method based on monitoring the performance degradation data of oil–paper insulation. In this study, the remaining life prediction model of oil–paper insulation is established according to the Wiener stochastic process. The parameters of the model are iteratively updated by using the Bayesian rule and maximum expectation algorithm. The objective of remaining service life prediction of transformer oil–paper insulation is achieved. In the laboratory, multiple groups of oil–paper insulation samples undergo an ageing test at 130°C. Certain amount of performance degradation data is obtained by continuously monitoring the oil–paper insulation. Along with the prediction method of remaining life, the accuracy of the remaining life prediction of transformer oil–impregnated paper is verified when the model parameters are updated. This is a significant guiding factor for predicting the remaining life through the performance degradation data of the continuously operating transformer.