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It is well established that copper sulfide is formed due to reaction of sulfur with copper conductors in transformers and reactors. However, there is very little experimental evidence to demonstrate copper sulfide diffusion into bulk of paper. Diffusion experiments have been carried out on three samples of kraft paper having different thickness. Positron Annihilation Lifetime Spectroscopy has been used to investigate the possibilities of copper sulfide diffusion into bulk of paper. This study has demonstrated that copper sulfide can diffuse into the bulk of paper leading to either increase or decrease in free volume of paper. The reasons for changes in free volume of paper due to copper sulfide deposits are explained. The consequences of copper sulfide diffusion on PD, voltage-current characteristics under ac and volume resistivity are discussed. Electric field simulation has been used to explain the effects of Cu ions and copper sulfide formation on electric stress distribution across paper. [ABSTRACT FROM AUTHOR]

The effects of furfural generation and partitioning on the aging assessment of oil-paper insulation of power equipment were investigated. Oil-paper samples with various furfural contents were prepared using an accelerated thermal aging experiment. The mass of the furfural generated during the aging of insulation paper was calculated and used to establish the quantitative equation between the accumulated furfural and the degree of polymerization (DP) of the insulation paper. Results showed that the reciprocal of the DP value was linearly related to the amount of furfural generated by the insulation paper. Effects of temperature, moisture, and temperature on the furfural partitioning ratio between oil and paper were analyzed using a furfural partitioning experiment, and a furfural partitioning model was established. Results showed that the furfural partitioning ratio in oil was positively correlated with temperature and moisture but negatively correlated with the DP of the insulation paper. A method for assessing the age of an insulation paper by integrating the furfural generation and partitioning models was proposed and applied on a 500-kV reactor that was returned for factory maintenance. The application result indicated that the method could accurately assess the overall aging condition of the oil-paper insulation of the power equipment. [ABSTRACT FROM AUTHOR]

Several miniaturized viscometers, or microviscometers, have been developed exploiting numerous rapid prototyping techniques. Among them, paper microstrips, famously known as microfluidic paper-based analytical devices ($\mu $ PADs), have become popular due to their cost-efficacy, simple fabrication, fast response, and easily disposable. Many fabrication methods are existing to develop paper microstrips. Herein, an alternative fabrication method is proposed where fused deposition modeling (FDM)-based 3-D printer (3DP) has been employed using polycaprolactone (PCL) filament. F, image processing has been utilized to measure viscosity in such microfluidic domain. Viscosity was calculated by measuring the time taken by the fluid to cover a fixed length between two spots in the microchannel based on the programed and color-coded regions-of-interest. The image processing program was developed considering the change in the gray scale in the virtual region of interests (ROIs) in the microchannel during the fluid flow in the paper microstrips. A 3-D printed handheld platform, containing raspberry pi with on-board camera and display, was developed to execute the image processing and automate the entire work flow. In the proposed device, the accuracy was measured to be >92%. [ABSTRACT FROM AUTHOR]

A substantial quantity of testing has been performed on the degradation of paper insulation over the decades. The aim being to better educate the electrical industry on how to best operate expensive assets, such as transformers. The longevity of paper insulation is frequently tested using accelerated ageing experiments, where the effects of temperature and the chemical environment on paper lifespan can be studied. Such research has resulted in paper life expectancy curves being published by the IEEE and the IEC. The investigations tend to use sealed vessels. However, the disadvantage of using this method is that the water content of the paper changes during the ageing process which then changes the ageing rate. In these ageing experiments the water and oxygen content was controlled using a special test rig to compare the ageing rate to previous work and to determine the ageing effect of paper by combining temperature, water content of paper and oxygen content of the oil. We found that the rate of paper ageing can be more accurately determined by controlling the water and oxygen during the experiment which then produced noticeable changes in predicting life expectancy. [ABSTRACT FROM PUBLISHER]

Oil-paper insulation ageing of transformer has characteristics of spatial locality due to uneven temperature distribution. The transformer is sealed, it is difficult to obtain the local ageing state of oil-paper insulation by sampling directly. Currently, there are no effective detection method to detect the insulation state of local regions. The oil-immersed paper resistivity inversion method can nondestructively assess the local state of oil-paper insulation. However, the current inversion methods still have shortcomings and need to be improved. In this paper, combining the back propagation neural network (BPNN) and Newton downhill method (NDM), an improved inversion method is proposed to optimize the current inversion method, so as to reduce the effect of initial value on it and make calculated results converge better. Finally, a 3D 10 kV transformer model is established to verify the effectiveness of the proposed method. The resistivity calculated by the improved method show that the method can provide initial resistivity values for technicians and improve the convergence and accuracy of current inversion method, which is more suitable for extending to the engineering practice. [ABSTRACT FROM AUTHOR]

Interest in using vegetable oils as dielectric coolants in power transformers dates back to the early studies on linseed- and castor- based fluids as possible replacements of mineral oil. However, interest in vegetable oils was lost due to their high viscosity and their tendency to oxidize. But, in the early 1990s and due to environmental concerns, the interest in dielectric fluids based on vegetable esters re-emerged. As a result, two vegetable ester? based oils were developed, namely, BIOTEMP, developed by ABB, and FR3?, developed by Cooper Power Systems. [ABSTRACT FROM PUBLISHER]

It is state-of-the-art to describe the dielectric behavior of an insulation material by its permittivity and its specific electric conductivity in order to estimate the dielectric stress of an insulation system. Thus, the electric field at DC voltage stress is determined according to the stationary electrical conduction field with the electric conductivity of the insulation materials. However, at oil-insulated arrangements a higher field strength in front of bare metal electrodes at high DC voltage stress occurs, which is not explainable with this model. Therefore, a charge carrier-based approach is presented to describe the dielectric behavior of the oil-paper insulation. It describes the movement of charge carriers and their effect on the electric field strength. Their drift leads to an accumulation of charge carriers in front of electrodes which results in a higher field strength in these areas, which can be calculated numerically using the Poisson-Nernst-Planck equation system. Compared to the conductivity-based model fundamental differences can be shown. Breakdown experiments qualitatively confirm the expectations according to the charge carrier-based approach. The results show that the charge carrier-based field distribution has to be considered for modelling the electrical field strength distribution at high DC voltage stress. They also show, that the dielectric behavior of these arrangements cannot be explained according to the state-of-the-art model. [ABSTRACT FROM AUTHOR]

Microfluidic paper-based analytical devices ($\mu $ PADs) are a clean-room free, cost-effective, and self-pumping flow-based rapid prototyping technique, which is compatible with a varying range of fluids. Until now, $\mu $ PADs have been primarily fabricated using crayons, and plotting-machine and solid-ink printers. These devices can be easily employed for various detection schemes, such as electrical, electrochemical, and optical. The presence of a capillary effect in the chromatograph paper has made $\mu $ PADs independent of a passive device, such as pumps and valves. In this paper, an alternative and a novel method is proposed to achieve the $\mu $ PADs effortlessly using a 3-D printer (3DP), which has many advantages over the existing methods. For creating hydrophobic barriers for microchannel walls, polycaprolactone (PCL) filament was used with fused-deposition modeling (FDM) 3DP. PCL filaments were deposited on the chromatography paper followed by heating for determining the overall dimension and depth of the microchannel at which PCL melts and penetrates into this paper. The $\mu $ PADs are characterized and optimized for two parameters. First, fabrication parameters, such as heating temperature and time duration, were used for the creation of the hydrophobic barrier using a hot air oven. Second, the microchannel parameters, such as microchannel width, boundary thickness, chromatography paper grade, and microchannel source shape (rectangular, triangular, and circular) were used for the fluid-flow by measuring the time taken by fluid to travel a fixed length of the microchannel. After rigorous analysis, it was found that for the creation of the hydrophobic barrier, $\mu $ PADs heated between temperature 120°C to 150°C require 30 min. Under optimized conditions for the fluid flow, the chromatography paper grade 1441 with a triangular source microchannel was found to be best. This paper provides an alternate, simple, and optimized method toward the development of the application-specific $\mu $ PADs, such as the micro-viscometer, which, in turn, can be widely used to monitor various types of fluids including human bodily fluids. [ABSTRACT FROM AUTHOR]

The methodologies used by various researchers to determine the moisture diffusion coefficients in Kraft paper and pressboard transformer insulation are reviewed. Moisture concentration profiles during insulation drying, calculated using the various coefficients, are presented. [ABSTRACT FROM AUTHOR]

This work investigates the effect of alternating current partial discharge (AC PD) byproducts on the dielectric frequency response (DFR) of oil-paper insulation comprising of a small cavity, in the frequency range of 1.0 mHz to 1.0 kHz. The investigations were done by utilizing experimental results in combination with a Finite Element Method (FEM) model. The results presented in this paper show that ageing by-products in the cavity (PD stressed volume) alone will not result into the change in DFR of oil-paper insulation. According to simulation results, the significant change in the DFR results is mainly caused by PD by-products (positive and negative charges, and electrons) which tend to conduct or diffuse into the bulk of oil-paper insulation. The change in a dissipation factor curve due to PD by-products was observed to occur mainly in the middle and low frequency regions. The results indicate that the dissipation factor curves in the middle and low frequency regions depend on the level of PD by-products in oil and paper, respectively. [ABSTRACT FROM AUTHOR]

This paper proposes a method for estimation of tanδ of cellulosic parts in oil-paper insulation from frequency domain spectroscopy based on equivalent circuit model of oil-paper insulation in real-life transformers. Existing literature shows that overall condition of oil-paper insulation in transformer can be assessed by conventional frequency domain spectroscopy. Also, the condition of oil can be separately and easily predicted through analyzing its dielectric properties by taking out the oil samples from transformer. However, it is quite difficult to assess the dielectric properties of cellulosic parts in oil-paper insulation as it cannot be directly accessed from outside for an operating transformer. Considering the aforesaid fact, this paper presents a segregated equivalent circuit model of composite oil-paper insulation that can separately estimate the tanδ profiles for oil as well as cellulosic parts. The tanδ profiles of cellulosic parts obtained from the equivalent circuit model have been validated experimentally. Results show that the tan? profile obtained from experimental result holds good agreement with that of the proposed model. [ABSTRACT FROM PUBLISHER]

Paper materials are used as the insulation of power transformers. Over time these materials slowly degrade, until they reach a point when they no longer function effectively as transformer insulation, and the transformer has then reached its end of life. The aging rate of paper is affected by temperature, water, oxygen and acids. Investigations have been performed previously on Kraft and Kraft thermally upgraded types of paper. However, a different type of paper used in transformer insulation, Grade 3 presspaper (which contains cotton), has not been extensively tested and compared to Kraft paper. In these experiments we studied the aging rate of Grade 3 presspaper and compared it to our previous studies of Kraft paper. Traditionally, the aging rate of paper has been studied in sealed vessels. The problem with this approach is that the chemical environment within the vessel will change during aging, and so the aging rate will be affected. In our experiment setup we controlled the water and oxygen content to more accurately determine the aging rate. Similarly to Kraft paper, the aging rate of Grade 3 presspaper with the same water content increased with oxygen content in the oil. Life curves were developed based on the water content of the paper and the oxygen content of the oil. [ABSTRACT FROM AUTHOR]

Dielectric response testing is a non-destructive insulation testing method that is widely used for assessing insulation properties. Time-and frequency-domain dielectric spectra are closely dependent on insulation conditions. In comparison with the time-domain spectrum, the frequency-domain dielectric response under sweep sinusoidal excitation has a stronger anti-interference capability and a more comprehensive insulation information. However, the wide application of the measurement using the frequency-domain dielectric response under sweep sinusoidal excitation is hindered by its long testing time. A possible solution is obtaining the frequency-domain spectrum by transforming the tested time-domain spectrum, such that the time- and frequency-domain spectra can be obtained in one measurement. Polarization depolarizing current measurement under DC excitation is a common time-domain testing method for time-frequency-domain conversion. However, such conversion is valid only at extremely low frequencies (less than 0.05 Hz), indicating a slight overlap with the frequency range of the measurement using the frequency-domain dielectric response under sweep sinusoidal excitation. Moreover, the effective conversion frequency range cannot be controlled manually, and the measurement using time-domain dielectric response under DC excitation is hindered by the anti-interference capability due to micro polarization-depolarization current. In addition, scholars have found nonlinearity in a partial insulation system. As the bridge of the traditional time-frequency-domain conversion, a linear extended Debye model cannot accurately reflect insulation materials that exhibit nonlinear characteristics, thereby further limiting the application scope of time-frequency-domain conversion. This study introduces the system identification theory to demonstrate the problems existing in the traditional time-frequency-domain conversion and proposes an improved time-domain testing method based on the previous work. The improved method extends the effective frequency range of time-frequency-domain conversion and emphasizes the comprehensive analysis of the insulation by combining the measured time-domain spectrum and the frequency-domain spectrum conversed from time-domain data. [ABSTRACT FROM AUTHOR]

The Last decade saw significant growth in the digital terrestrial television (DTT) subscribers. The High peak-to-average power ratio (PAPR) of the transmitted signal is implied by the large fluctuations in its amplitude, which is a serious issue in the contemporary and next generation DTT broadcasting systems. These large fluctuations prevent feeding the high power amplifier (HPA) at an operating point near its non-linear (NL) saturation region, thereby lowering its power efficiency. For a better future, energy-efficient green communications is the need of hour. This paper focuses on digital predistortion (DPD), which is among the widely used techniques for HPA linearization in order to minimize the NL effects. DPD technique requires a feedback signal. This paper proposes a novel adding signal-based digital predistortion, where the output of the HPA is gradually linearized by adding a signal at the input in an iterative manner. By Taylor series approximation, the DPD problem can be posed as a convex one. We prove that a tighter upper bound exists for the convergence factor and instead of directly solving the convex problem, we pick a convergence factor value within its bounds that offers a good trade-off between convergence speed and residual error value. The simulation results show that the proposed technique can quickly linearize the HPA with good convergence. [ABSTRACT FROM AUTHOR]

This paper proposed a simulation method for the charge transport in single-layer oil-paper insulation. The method of transient upstream finite-element method (FEM) is derived in order to calculate the time variation of charge densities in medium. The numerical simulation of charge transport in the single-layer oil-paper insulation is realized by applying the transient upstream FEM to the transport equations of bipolar charges. With reasonable microparameter, the charge transport in an experimental object is simulated. The simulation results are consistent with the experimental data. A bent model of oil-paper insulation is analyzed to study the charge distribution under the actual condition. This paper provides an exploratory research to the simulation of charge phenomenon in oil-paper, and has guiding significance to the design of oil-paper insulation. [ABSTRACT FROM AUTHOR]

The temperature distribution is vital to the lifetime and reliability of converter transformer bushings. However, the temperature distribution of epoxy impregnated paper converter bushings under a certain current has usually been calculated through the two dimensional model, without considering the heat convection and radiation effects. In this paper, using the computational fluid dynamics (CFD) and finite element method (FEM) analysis, a 3-D electromagnetic-fluid-thermal analysis method has been proposed. With the considering of heat conduction, heat convection and radiation, the temperature distribution of the converter transformer bushing has been simulated according to the actual operating environment. The temperature and velocity distribution of the converter transformer bushing has been obtained. Moreover, the simulation results have been compared with the experimental results to verify the accuracy of the simulation method. The simulation results, especially for the inner conductor, external conductor and the epoxy impregnated paper, are very close to the experimental results and the maximum temperature difference percentage is within 10 %, which indicates the accuracy and effectiveness of the electromagnetic-fluid-thermal analysis method proposed. [ABSTRACT FROM AUTHOR]

The paper presents new diagnostic method applied to assess aging degree for paper-oil insulation used in professional electrical power device, primarily including medium and high power transformers. The described method is based on modified diagnostics using the recovery voltage effect occurring in dielectrics (RVM ? Recovery Voltage Methods). Modification of the RVM method applied so far, which is now used only to assess moistening degree for paper-oil insulation in power transformers, consists in a new parametric analysis of recovery voltage time characteristics. Simulation and experimental tests carried out in laboratory conditions for adequately prepared insulation samples have proven that the time-constant of recovery voltage decay (?R_MIN) is the most susceptible parameter as regards quantitative change in the function of aging of the examined insulation. This conclusion is also confirmed by statistical studies, in which a multi-parameter variance analysis method has been applied. An original equivalent circuit diagram of the insulation has been used to simulate aging degree of paper-oil insulation samples in numerical tests. The diagram is based on the Cole-Cole type dielectric response model. [ABSTRACT FROM AUTHOR]

Dielectric response measurements in either time or frequency domain are being assessed in modern times for condition monitoring of transformer oil-paper insulation. Proper interpretation of the dielectric test results requires understanding of the physical processes taking place in the insulation structure during such tests. It is thus necessary to establish proper mathematical and analytical formulations of the insulation behavior. Dielectric response functions of various forms based on the classical ?single relaxation time? Debye model have been proposed by various researchers to model the experimental data. In complex dielectrics, it seems however, that the overall response be represented by a distribution of relaxation times (or frequencies), rather than a single ?average? response characteristic. The present contribution provides in brief, the mathematical background for estimating the dielectric response functions used so far for modeling dielectric response measurement data. Function representing distribution of relaxation frequencies has also been estimated. Experimental results on laboratory test samples and field transformers have been presented to study and understand the effects of insulation status and operating conditions on test data. [ABSTRACT FROM AUTHOR]

The service life of a transformer is determined by the condition of its oil?paper insulation. A modified Cole?Cole model was introduced to describe the frequency domain spectroscopy (FDS) curves based on the classic Debye relaxation model and thereby accurately determined the ageing state of the insulation of a power transformer using FDS. Oil?paper insulation samples with different ageing states are prepared under laboratory conditions, and a characteristic parameter is extracted to quantify their ageing states after a detailed investigation of the frequency domain dielectric properties of the samples. Results reveal that the modified Cole?Cole model, including the ? relaxation components, dc and hopping conductivity components, can be employed to effectively model the frequency dielectric characteristics of oil?paper insulation. Furthermore, the extracted characteristic parameter from this model, ??, can be utilized in the quantitative evaluation of the ageing states of transformer insulation. A case example is discussed to demonstrate the applicability of the proposed technique in the condition assessment of field power transformers. [ABSTRACT FROM AUTHOR]

In this paper the accelerated aging experiments of oil-paper insulation are carried out to simulate the oil-paper aging process under normal thermal aging process. On the basis of the results of accelerated aging experiments, how the deviation degree of aging status change under the same aging factors is studied, and a method to calculate the failure probability due to the loss of mechanical strength of the insulation is put forward. This paper presents an approach for economic assessment on insulation diagnosis through accelerated aging experiments. The foundation of this approach for economic assessment on insulation diagnosis is to establish condition simulation method of triple relationships between condition status, aging time and failure probability according to data from accelerated aging experiments. The conclusions are made that the economic and technical factors can affect the optimum life cycle cost of each maintenance strategy, which consequently affects the economic feasibility of condition-based maintenance strategies. [ABSTRACT FROM AUTHOR]

The presence of moisture in oil impregnated paper insulation (OIP) is detrimental to its long time performance. Until recently, it was thought insulation ageing was only a function of temperature and electrical stress. It has now been realized that moisture in all its forms causes rapid degradation of the electrical and mechanical properties with time. In this study, insulation paper samples were conditioned for desired level of moisture and were impregnated with premium quality transformer oil. The oil impregnated samples with 1 to 3 % moisture content were aged at 90 to 130°C. The indices for determining the extent of ageing considered in this work are degree of polymerization (DP), furan, carbon monoxide and carbon dioxide content. These quantities were monitored throughout the ageing experimental run. End-of-life (EOL) criterion used here is the reduction in the value of DP. Phenomenological models for estimating the service life of insulation are proposed and are validated against actual experimental data. [ABSTRACT FROM AUTHOR]

Dielectric parameters of insulation used in High voltage equipments like power transformers are dependent on insulation size and geometry. As a result parameters evaluated from the model of one insulation system finds limited use in predicting the condition of other. Poles calculated from branch parameters of insulation model, on the other hand are independent of insulation geometry. However such technique requires accurate modeling of dielectric response function. Conventional Debye model does not consider the effect of temperature gradient that exists across the length of the insulation during its operation. In the present paper it is shown that for more accurate modeling and better understanding of dielectric response of oil-paper insulation, a new model which considers the effect of temperature gradient on insulation properties, is necessary. The present paper reports a methodology that is capable of identifying such a model using PDC measurement data. It is also shown that use of conventional Debye model overestimates the pole values and the error increases with usage of the insulation. [ABSTRACT FROM AUTHOR]

Moisture dynamics in cellulosic insulation can be estimated using a mathematical model of diffusion based on Fick's second law [1], [2]. The main parameter of this mathematical model is the moisture diffusion coefficient, and the precision of the model is dependent on using an accurate value of this coefficient. Various researchers have obtained expressions for the moisture diffusion coefficient for cellulosic insulation, such as Kraft paper or pressboard, applying different methodologies [3]–[10]. Several values of the diffusion coefficient can be found in the literature represented by mathematical expressions, tables, or experimental curves, relating the dependence of the coefficient with the local moisture concentration and temperature. Some of these coefficients have been determined for nonimpregnated insulation (mainly Kraft paper and pressboard) and others for oilimpregnated paper. Most of these coefficients were determined more than 25 years ago [11], and until now, no coefficients have been proposed for oil-impregnated pressboard. [ABSTRACT FROM AUTHOR]

In this paper, we present an update to the models used to calculate the remaining life of transformer paper insulation. A drawback to the current IEEE method is that it does not take into account the availability of water and oxygen on the life expectancy of Kraft paper insulation. We therefore set out to test an algorithm which does take these into account. For our investigation, we loaded three test transformers and ran them to near their end of life. Kinetic equations were applied to model the fall in the degree of polymerization of paper. Our model showed better agreement with the test results than that given from using the IEEE standard. The IEEE standard gives life expectancy for Kraft paper being aged in minimal oxygen under dry conditions, which is not necessarily representative of an old transformer. Wet paper and using high levels of oxygen can age nearly 40 times faster. The IEEE method needs to take the synergistic effect of water and oxygen on increasing the rate of paper aging into account. [ABSTRACT FROM PUBLISHER]

The presence of condensate inside the dryer cylinders results in a significant increase in the power and torque required until the condensate transitions to the rimming stage. This paper evaluates the effect of the condensate during the starting of a dryer section using the experimental curves reported by several authors, as well as a dimensionless model of the input power as a function of the condensate quantity and roll velocity. Through the evaluation of a nine-cylinder dryer section for various condensate quantities and varying number of cylinders containing condensate, a comparison is made to the power requirements of several actual paper machine dryer sections undergoing various starting procedures. These comparisons indicate that if the percent condensate (\condensate volume/full cylinder volume \times 100) in the range of 0.5%–1%, or greater, is nominally assumed to be present, then the sizing of the section drive capacity must take into consideration the additional indrive load resulting from this condensate. Options are proposed to consider the effect of the condensate without increasing the Technical Association of the Pulp and Paper Industry recommended drive capacity of dryer sections. [ABSTRACT FROM PUBLISHER]

Moisture is one of the key variables that must be considered when determining the load profiles that can be safely applied to a transformer. The presence of high amount of water accelerates the aging rate of the transformer's solid insulation, shortening the life expectancy of the equipment. Moreover, the dynamic processes of moisture migration between paper and oil must be considered in order to avoid a potential cause of failure, such as the formation of bubbles in the paper–oil interface, or the moisture saturation and the subsequent formation of liquid water in oil. These processes are linked to the changes in temperature; however, within the transformer, both processes have very different time constants, which complicates the analysis. In this paper, a mathematical model is presented, which allows us to study the moisture dynamics in a transformer. The model considers a multi-physical approach incorporating a thermal module and a moisture dynamic module that makes it possible to analyze the behavior of the moisture for a certain load profile. Some application cases are included in this paper to illustrate the model operation. [ABSTRACT FROM AUTHOR]

The iso-margin method based on the classical analytical equations is widely used in the development of extra high voltage (EHV) bushing. Therefore, its effectiveness and feasibility have been fully validated. However, with the theoretical formula, it is difficult to evaluate the influence of stray capacitance and temperature on the internal electric stress of the ultra high voltage (UHV) bushing. It?s necessary to further improve the traditional iso-margin method. Firstly, the basic principle of iso-margin method has been briefly described. After that, the E-field distribution of condenser bushing was investigated on the Finite Element Method (FEM) computing platform. Then, the mathematical model of the advanced equal margin design method was established. Furthermore, this paper presents the program flow of optimization which combines the simulation of electro-thermal coupling process and the particle swarm optimization (PSO) algorithm. The proposed methodology was applied to the design of the prototype of the UHV resin impregnated paper (RIP) oil-SF6 bushing, which realizes the uniform axial E-field distribution of the bushing condenser. Meanwhile, the partial discharge margin between adjacent foils can be equal. Moreover, the hot-spot temperature is lower than the operation limiting temperature of the RIP material. The bushing condenser was fabricated according to the optimal structure design. The prototype of bushing has passed through all the type tests. In this paper, the FEM electro-thermal coupling simulation and the advanced equal margin design method were applied to the inner insulation structure optimization of the UHV RIP oil-SF6 bushing. Meanwhile, the proposed methodology provides some theoretical guidelines for the future research and development of other types of bushing on the UHV level. [ABSTRACT FROM AUTHOR]

This paper presents a novel technique to estimate activation energy of oil-paper insulation in power transformer from time domain spectroscopy recoded at any given temperature. Existing literatures show that, remaining life of transformer insulation can be estimated if the information regarding its activation energy can be obtained. The activation energy of transformer insulation can be obtained based on its frequency spectrum measured at two different temperatures. However, it is quite difficult to record the frequency spectrum at two different temperatures for the transformers which are operating in the field. Considering the aforesaid difficulty, in the present work, a technique is adopted that can evaluate the activation energy of transformer insulation based on the time domain spectroscopy data recorded at a temperature. In order to investigate the effectiveness, the proposed technique is applied to a test sample having preset moisture content to estimate its activation energy. The estimated activation energy using the proposed technique, is validated with the results obtained using other existing technique. The proposed technique is then applied to several real-life power transformers to estimate their corresponding activation energy. The estimated activation energy for the transformers is used to assess their remaining life. [ABSTRACT FROM PUBLISHER]

Motivated by the fact that living cells use molecular circuits (i.e., a set of chemical reactions) for information processing, this paper investigates the problem of designing molecular circuits for demodulation. In our earlier work, we use a Markovian approach to derive a demodulator for diffusion-based molecular communication. The demodulation filters take the form of an ordinary differential equation, which computes the log-posteriori probability of a transmission symbol being sent. This paper considers the realization of these demodulation filters using molecular circuits assuming the transmission symbols are rectangular pulses of the same duration but different amplitudes, i.e., concentration modulation. This paper makes a number of contributions. First, we use time-scale separation and renewal theory to analytically derive an approximation of the demodulation filter from our earlier work. Second, we present a method to turn this approximation into a molecular circuit. By using simulations, we show that the output of the derived molecular circuit is approximately equal to the log-posteriori probability calculated by the exact demodulation filter if the log-posteriori probability is positive. Third, we demonstrate that a biochemical circuit in yeast behaves similarly to the derived molecular demodulation filter and is therefore a candidate for implementing the derived filter. [ABSTRACT FROM AUTHOR]

Marbling creates stone-like or intricate abstract decorations from inks floating on water or gel. Instead of using fluid dynamics to simulate marbling, a proposed method takes a mathematical approach with closed-form expressions. This method improves control, ease of implementation, parallelism, and speed, enabling real-time visual feedback and creation of vivid flowing animations. Users can start designs from a blank sheet, raster images, or videos. When starting with a blank sheet, this method can produce compact resolution-independent vector output. The transforms for the marbling operations all have inverse transforms. Forward application generates compact resolution-independent vector-based output; inverse application generates pixel-based output. In both cases, the closed-form expressions preserve the designs' quality and sharpness. Extensive comparisons with other digital marbling methods demonstrates this method's efficiency and effectiveness. Applications of this method include surface detail rendering for 3D objects, interactive video processing, and scene decoration. The video at http://youtu.be/ZgVbIaKhC_4 shows the application of simulated marbling to a video stream. [ABSTRACT FROM PUBLISHER]

Moisture content in transformer is a prime indicator of its insulation condition. The presence of moisture accelerates the aging of cellulosic paper insulation thereby reducing the dielectric as well as the mechanical strength of the insulation. In the conventional method for sensing moisture content in transformers, sinusoidal excitation is generally applied on the oil–paper insulation system for two cycles from 0.1 mHz to 1 kHz. However, the application of sinusoidal excitations at discrete measurement frequencies leads to long measurement time during low frequency measurement (from 0.1 mHz to 1 Hz), which is a practical problem. Besides, as the moisture content increases, the transformer insulation no longer behaves as a linear time-invariant system. Therefore, non-linear modeling of insulation is necessary for accurate moisture sensing in transformers. Considering these two facts, in this study a non-linear Wiener model of transformer insulation using sine sweep excitation is proposed for reliable sensing of moisture content at reduced measurement time. It was observed that the proposed non-linear Wiener model has better moisture-sensing capability, thereby providing more accurate information regarding the insulation condition in comparison with the linear model. Moreover, an appreciable reduction in the total measurement duration was observed, enabling transformer diagnosis to be conducted quickly compared to the conventional method. [ABSTRACT FROM AUTHOR]

Real-time estimation of the modulus of elasticity $(E)$ in paper machines would enable it to be controlled, improving final product quality and reducing the occurrence of sheet breaks. This paper develops a novel topology to estimate $E$ on web machines based on an adaptive observer structure that combines model reference adaptive control with a closed-loop observer using field signals such as tension force, velocity/position, and torque. The evaluation of the proposed topology is performed on the dryer–calender span of the dry-end section of a lightweight coated paper machine. Results show a fast and accurate estimation of $E$, confirming the robustness of the adaptive observer structure. [ABSTRACT FROM PUBLISHER]

Polarization-Depolarization Current (PDC) analysis is a well known technique for condition monitoring of oil-paper insulation in power transformers. However, due to variation in insulation geometry, information obtained through analysis of PDC measured for one transformer cannot be used for predicting condition of another transformer even if the loading history of the two units are similar. Furthermore, parts of solid insulation closer to winding are exposed to much higher temperature than the parts away from it. Prolonged exposure to this temperature variation leads to nonuniform aging in cellulosic parts. It is reported that Modified Debye Model (MDM) is capable of modeling this non-uniform aging. In the present work it is shown that a parameter sensitive to insulation condition can be obtained from Transfer Function of MDM. Several laboratory samples having different physical dimensions has been constructed. PDC data recorded from these samples are used to obtain the performance parameter (which is less influenced by insulation geometry) and its relation to paper moisture content. The results obtained from the proposed method have been compared with that obtained using Frequency Domain Spectroscopy (FDS) based commercial instrument (IDAX 300) in the case of real-life power transformer. [ABSTRACT FROM AUTHOR]

Let us consider that someone is starting a research on a topic that is unfamiliar to them. Which seminal papers have influenced the topic the most? What is the genealogy of the seminal papers in this topic? These are the questions that they can raise, which we try to answer in this paper. First, we propose an algorithm that finds a set of seminal papers on a given topic. We also address the performance and scalability issues of this sophisticated algorithm. Next, we discuss the measures to decide how much a paper is influenced by another paper. Then, we propose an algorithm that constructs a genealogy of the seminal papers by using the influence measure and citation information. Finally, through extensive experiments with a large volume of a real-world academic literature data, we show the effectiveness and efficiency of our approach. [ABSTRACT FROM PUBLISHER]

In this paper, a new framework for path tracking is proposed through learning to drive like human beings. Firstly, the imitation algorithm (behavior cloning) is adopted to initialize the deep reinforcement learning (DRL) algorithm through learning the professional drivers’ experience. Secondly, a continuous, deterministic, model free deep reinforcement learning algorithm is adopted to optimize our DRL model on line through trial and error. By combining behavior cloning and deep reinforcement learning algorithms, the DRL model can learn an effective policy quickly for path tracking using some easy-to-measure vehicle state parameters and environment information as inputs. Actor-Critic structure is adopted in the DRL algorithm. In order to speed up the convergence rate of the DRL model and improve the learning effect, we propose a dual actor networks structure for the two different action outputs (steering wheel angle and vehicle speed), and a chief critic network is built to guide the updating process of dual actor networks at the same time. Based on this dual actor networks structure, we can pick out some more important state information as state inputs for different action outputs. Besides, a kind of reward mechanism is also presented for autonomous driving. Finally, simulation training and experiment test are carried out, and the results confirm that the framework proposed in this paper is more than data efficient than the original algorithm, and the trained DRL model can track the reference path with accuracy and has the generalization ability for different roads. [ABSTRACT FROM AUTHOR]

This paper analyses the inherent difficulties in measuring the horizontal electric field from lightning and proposes some solutions to mitigate the contamination effect of the overwhelming vertical electric field. The analysis is carried out with a set of time-domain equations for the calculation of the electromagnetic fields from lightning. As these equations are scattered in several publications, in this paper they are compiled and presented in a harmonized form. Moreover, one new expression for the vertical electric field slightly below the ground surface is presented. It is shown that the horizontal electric field at the surface of lossy ground can be measured with minimum disturbance caused by the vertical electric field if the field sensor is placed slightly below the ground surface. This paper also shows that the horizontal electric field above the ground surface could be measured with the help of a pair of field sensors conveniently arranged so that the influence of the vertical electric field on the measurement is cancelled. [ABSTRACT FROM AUTHOR]

The remaining useful life (RUL) of transformer insulation paper is largely determined by the winding hot-spot temperature (HST). Frequently the HST is not directly monitored and it is inferred from other measurements. However, measurement errors affect prediction models and if uncertain variables are not taken into account this can lead to incorrect maintenance decisions. Additionally, existing analytic models for HST calculation are not always accurate because they cannot generalize the properties of transformers operating in different contexts. In this context, this paper presents a novel transformer condition assessment approach integrating uncertainty modeling, data-driven forecasting models, and model-based experimental models to increase the prediction accuracy and handle uncertainty. The proposed approach quantifies the effect of measurement errors on transformer RUL predictions and confirms that temperature and load measurement errors affect the RUL estimation. Forecasting results show that the extreme gradient boosting (XGB) algorithm best captures the nonlinearities of the thermal model and improves the prediction accuracy among a number of forecasting approaches. Accordingly, the XGB model is integrated with experimental models in a particle filtering framework to improve thermal modeling and RUL prediction tasks. Models are tested and validated using a real dataset from a power transformer operating in a nuclear power plant. [ABSTRACT FROM AUTHOR]

The study on the scattering mechanism of breaking ship waves provides important theoretical basis to the ship detection and radar imaging in a marine environment. This paper presents a new procedure for evaluating the electromagnetic scattering field of breaking ship waves over a perfect electric conductor sea surface. In this paper, different forms of the near-field ship waves are obtained by the computational fluid dynamics (CFD) method, which provides a new means of analyzing a fully coupled fluid-structure interaction system in a detailed manner. Sufficient grids are used in the CFD numerical simulation to obtain the flow field information of the breaking waves. The accuracy of the breaking wave geometry has been improved obviously, which will lead to a better understanding of the electromagnetic scattering characteristics of breaking ship waves. Considering the multiple scattering between the ship hull and the breaking waves, the scattering field of the sea surface and the ship hull are evaluated by the forward–backward iterated physical optics algorithm. Both scattering characteristics of the breaking ship waves and distribution of the scattering coefficients are obtained. By comparing the bistatic scattering field in different situations, the numerical results show some important effects of the breaking ship waves, which are quite different from the effects of ship models. What is more, the time varying radar cross section of the breaking ship waves are presented based on the dynamic ship waves. [ABSTRACT FROM AUTHOR]

The rising cost of production testing for a system-on-a-chip (SoC) is one of the crucial matters to chip makers, due to long test time and costly automated-test-equipment. This paper proposes a spectral leakage-driven built-in self-test (BIST) scheme to precisely predict the nonlinearity of mixed-signal circuits in the loopback mode, thereby accomplishing cost-effectiveness (compared to previous BIST-based works). A digitally synthesized single-tone sinusoidal stimulus used for conventional harmonic testing is incoherently sampled by a device under test (DUT). The DUT output signal exhibits the correlation between the DUT harmonics and the spectral leakage introduced by the incoherent sampling. The DUT output signal is then fed to another DUT through a loopback path, so that the harmonics of a pair of DUTs are correlated with the spectral leakage on the loopback response; the magnitude of the spectral leakage is considered as a weighting factor on the harmonic magnitude of those DUTs. The correlation is quantitatively modeled as characteristic equations in , and postprocessing predicts the harmonics of the two individual DUTs, by simultaneously solving the characteristic equations using on-chip DSP core available in an SoC. Simulation and hardware measurements validated that this paper can be practically used for production testing by showing less than 0.3 and 0.6 dB of the prediction errors, respectively. [ABSTRACT FROM AUTHOR]

Analysis of Polarization-Depolarization Current, recorded from high voltage oilpaper insulation using insulation model is common among researchers. It is reported that paper insulation of power transformers undergoes non-uniform aging. Unlike Conventional Debye Model (CDM), Modified Debye Model (MDM) is capable of modeling such non-uniform aging. However, factors like insulation geometry affect the values of the MDM branch parameters. Therefore, model parameterized using data obtained from one insulation system finds limited use in assessing the condition of a different transformer, even with similar loading history and power rating. The present paper shows that a performance parameter, which is less sensitive to insulation geometry, can be evaluated from Transfer Function, TFM(s) of MDM. The parameter is the zero Z1 of TFM(s) which is located farthest away from the origin in the Left Half Plane of s-plane. The capability of Z1 as an insulation condition sensitive parameter is first tested on laboratory samples and then on data recorded from several real life power transformers. Results obtained for these transformers show that there is a good correlation between magnitude of Z1 and paper moisture content obtained from Frequency Domain Spectroscopy (FDS) using IDAX 300. [ABSTRACT FROM AUTHOR]

UHV DC wall bushing is the only channel connecting the valve hall and the DC electric field in the converter station. For the epoxy - SF6 gas composite insulation wall bushing, the main insulation material is the epoxy/crepe paper core and SF6 gas. The transient process of establishing the DC electric field for the wall bushing is impacted by the temperature gradient. In this paper the 3-D temperature field of the wall bushing has been simulated considering the effect of heat conduction, convection and radiation. The simulation results have been confirmed using a temperature rise experiment. The transient process of the wall bushing under the actual operation condition has been simulated using the gas saturation current density method. The temperature impact on space charge density in the core, the surface charge on the interface, and the electric field distribution on the bushing is investigated. In this way a theoretical basis is developed for the optimal design of the bushing that is conductive to the safe operation of the bushing. [ABSTRACT FROM AUTHOR]