Actual Transformer Research Articles

ベクトル磁気特性制御材の開発

There is rotational iron loss under the V-junction in the yoke in an actual transformer because not only alternating magnetic field but also rotational and elliptical magnetic field are generated. The rotational iron loss can not be grasped in the standard magnetic measurements because it is assumed that the vectors of magnetic flux density B and magnetic field strength H are scalar quantity in them. We have proposed a two-dimensional vector magnetic measurement technique which can measure the B-vector and H-vector that are in the different directions，additionally，which can grasp the rotational iron loss. There is also phase difference θBH between the B-vector and the H-vector. The iron loss is calculated by the inner product between the B-vector and the H-vector. Therefore，the iron loss increases depending on the θBH. We controlled the θBH by fining the magnetic domain，and developed a new electrical steel sheet，and named “a vector magnetic characteristic controlled electrical steel sheet” which can reduce the iron loss. This paper presents the detail measured results from a vector magnetic characteristic controlled electrical steel sheet.

Incorporating adaptability-related knowledge into support vector machine for case-based design adaptation

In case-based design systems, the adaptation operation based on similar cases is a difficult and complex step, and the more adaptable cases usually could make larger contribution for adaptation generation than less ones. Under this ideology, this paper addresses a new case adaptation method which uses support vector machine (SVM) incorporating adaptability-related knowledge provided by the retrieved cases, called adaptability-involving SVM (ASVM). The knowledge of adaptability includes the adaptability characteristic of old cases returned by the adaptability analysis and the guideline that the training data from adaptable case should be given higher weight to build SVM model. So the content of this work presented here consists of two parts. The first one is to explore the adaptable property of old cases by utilizing decision tree technology. The second one is to study the construction of ASVM adaptation model in terms of retrieved cases. We first employ the differences between test and retrieved cases to assemble the adaptation pattern data for ASVM model training. Then the higher adaptability coefficients are given to the training data from more adaptable cases than those from less adaptable cases. We adopt ASVM in actual power transformer design to illustrate its feasibility, and carry out comparison researches with different numbers of retrieved cases in the different data sets to validate its superiority, through comparing the adaptation error results with those provided by other classical methods. Empirical results show that ASVM is feasible and validated for case adaptation.

Improved Power Transformer Winding Deformation Fault Diagnosis Method

according to analysing the generation principle of transformer winding deformation and its impact on the vibration signal, and make a large number of trial, it can be found in addition to the fundamental frequency component that can reflect the failure, the new characteristic frequency which conclude 50Hz frequency component and some of its harmonic components, the harmonic components of the fundamental frequency can also reflect the failure. Transformer winding deformation fault diagnosis method is proposed based on the relationship between the characteristic frequency, it can not only diagnose whether the failure inside the transformer windings, but also determine the type of fault. In order to verify the proposed method, deformation fault is set to the actual transformer winding. After de-noising, discounted processing, the acquisition monitoring points of vibration signal is used by the proposed method, and the actual transformer is diagnosed, The diagnostic result is same with actual failure. It is shown that the proposed diagnostic method is accurate and feasible.

Application of Wavelet Transform to Obtain the Frequency Response of a Transformer From Transient Signals—Part II: Practical Assessment and Validation

This paper presents a practical assessment and validation for the new proposed approach based on the continuous wavelet transform (CWT) to obtain the frequency response from online transient signals for an actual transformer. Apart from the mathematical procedure, an electronic system was also designed and implemented in order to inject superimposed controlled pulses to the power system (50/60 Hz) wave. The results show improved performance of the wavelet transform compared to the Fourier transform, for transient signal analysis to be applied on a nonintrusive transformer monitoring approach. Particularly, this new approach enables overcoming some problems related to the signal filtering and the signal processing in an online frequency-response analysis transformer diagnosis. This paper is presented in three parts. Part I showed the main theoretical basis of this approach. The current Part II shows a practical assessment based on tests performed in a three-phase transformer of 1150/345 V-5 kVA and in a single-phase transformer of 13200/240 V-15 kVA. Part III shows the performance of this new approach on transformers being diagnosed under real conditions.

Study on Mechanical State Diagnosis of Power Transformer Winding Based on Vibration Method

This paper uses the vibration method to diagnose the mechanical state of transformer winding,directed against the fact that the accuracy of the mechanical fault diagnosis in transformer winding is not high. It collects the load test vibration signal of transformer winding in normal and abnormal state, analyzes the vibration signals in different states, and use the vibration frequency and load current matching to judge the winding condition. By setting the different faults to the actual transformer winding of S11-M-500/35 type, it uses the vibration method to do the diagnosis analysis. And the research content is of great significance for the promotion and application of vibration analysis method.

Magnetic Properties Evaluation of Grain-Oriented Electrical Steel Sheets Under Bending Stress

This paper investigates the influences of bending stress and annealing on magnetic properties of grain-oriented electrical steel sheets. Grain-oriented electrical steel sheets under different levels of bending stress are measured. The actual wound core transformer model that applied those magnetic properties is analyzed. The influences of bending stress and annealing on the behavior of the flux of an actual wound core transformer made by rolling electrical steel sheets are verified.

Multi-Secondary Transformer: A Modeling Technique for Simulation - II

Power Transformers with more than one secondary winding are not uncommon in industrial applications. But new classes of applications where very large number of independent secondaries are used are becoming popular in controlled converters for medium and high voltage applications. Cascade H-bridge medium voltage drives and Pulse Step Modulation (PSM) based high voltage power supplies are such applications. Regulated high voltage power supplies (Fig. 1) with 35-100 kV, 5-10 MW output range with very fast dynamics (<TEX>${\mu}S$</TEX> order) uses such transformers. Such power supplies are widely used in fusion research. Here series connection of isolated voltage sources with conventional switching semiconductor devices is achieved by large number of separate transformers or by single unit of multi-secondary transformer. Naturally, a transformer having numbers of secondary windings (~40) on single core is the preferred solution due to space and cost considerations. For design and simulation analysis of such a power supply, the model of a multi-secondary transformer poses special problem to any circuit analysis software as many simulation softwares provide transformer models with limited number (3-6) of secondary windings. Multi-Secondary transformer models with 3 different schemes are available. A comparison of test results from a practical Multi-secondary transformer with a simulation model using magnetic component is found to describe the behavior closer to observed test results. Earlier models assumed magnetising inductance in a linear loss less core model although in actual it is saturable core made-up of CRGO steel laminations. This article discusses a more detailed representation of flux coupled magnetic model with saturable core properties to simulate actual transformers very close to its observed parameters in test and actual usage.

Probabilistic Analysis of Life Cycle Cost for Power Transformer

The selection of power transformer is very important to power sector. Most methods are utilized according to the initial cost and don’t consider the synthetical evaluation of economy and technology. Based on previous research, this paper addresses a new practical probabilistic life cycle cost model. Then, in order to demonstrate the practicability of probabilistic life cycle cost for the power transformer, illustrative investment alternatives of actual power transformers are discussed. From the result of the numerical investigation, it may be positively stated that the optimum investment alternative for the power transformer based on the probabilistic life cycle cost model proposed in this study will lead to a more rational, economical and effective procedure compared with the conventional method only considering the initial cost.

Flow and heat distribution analysis of different transformer sub-stations

This paper describes CFD investigation on the flow and heat transfer in transformers at different sub-station buildings. The analysis aimed to determine the cooling capability of the existing transformer building employing natural ventilation system to dissipate heat sufficiently when new dry-type transformer operating under full load condition is used. The transformer and building models were developed based on the actual transformer configuration in operation at three different locations in Malaysia. The calculation was carried out on three different types of sub-stations namely stand-alone, attach-to-building and underground. The effect of natural ventilation speed and building volume on the transformer surfaces temperature are also investigated. It was predicted that the existing sub-station configuration is able to dissipate heat produced from the dry type transformer by using its natural ventilation system regardless of the sub-station types. However, the smallest building case shows relatively high surrounding temperature.

Suppressive effect and its duration of triazole-based passivators on copper sulfide deposition on kraft paper in transformer

The suppressive effect of triazole-based passivators such as 1,2,3-benzotriazole (BTA) and Irgamet 39 and duration of the suppressive effect on copper sulfide deposition are investigated by changing the time when passivators are added to oil. All corrosive sulfur tests were performed by the method stipulated by IEC 62535. In order to simulate the timing for adding passivators into actual transformers, preheated and non-preheated oils were used for corrosive sulfur test. Adding a passivator into preheated oil simulates the condition where a passivator is added into the transformer after a period of operation, and adding a passivator into non-preheated oil simulates the condition where a passivator is added before operation. Although the deposition rate of copper sulfide in preheated oil with the addition of passivator was lower in preheated oil without passivator, copper sulfide deposition still continued even while the passivator was detected in the oil. The result suggests that the precursors of copper sulfide have been already generated in preheated oil before adding a passivator. After the passivator was depleted in the oil, the period until onset of copper sulfide deposition in the preheated oil was shorter than in non-preheated oil since a protective complex layer was created on the copper surface and reaction with the passivator continued to prevent the deposition of copper sulfide precursors.

Estimation of Series Capacitance for a Three-Phase Transformer Winding From Its Measured Frequency Response

Recently, authors published a method to indirectly measure series capacitance (Cs) of a single, isolated, uniformly wound transformer winding, from its measured frequency response. The next step was to implement it on an actual three-phase transformer. This task is not as straightforward as it might appear at first glance, since the measured frequency response on a three-phase transformer is influenced by nontested windings and their terminal connections, core, tank, etc. To extract the correct value of Cs from this composite frequency response, the formulation has to be reworked to first identify all significant influences and then include their effects. Initially, the modified method and experimental results on a three-phase transformer (4 MVA, 33 kV/433 V) are presented along with results on the winding considered in isolation (for cross validation). Later, the method is directly implemented on another three-phase unit (3.5 MVA, 13.8 kV/765 V) to show repeatability.

Economic, Safe and Optimized Strategy of Operation of Transformer in Parallel Considering the Hot-Spot Temperature

In order to improve the economy of operation of transformer, this study presents a strategy to ensure the safety of power transformer for the situation of overload operation of parallel transformer. According to the variation of actual transformer operation, the authors divide the daily load curve into two typical time periods. In the high load operation period, except the constraint of minimum power loss for the economic operation, the factor for hot-spot temperature rise of the transformer should also be considered, so that an economic operation mode and parallel switching time could be obtained. This strategy estimates the hot spot temperature by the finite difference method, and obtains the optimal switching time through binary searching, according to the environment temperature and load curve. The analysis of the example of the operation of two sets of three winding transformers in parallel with different capacity shows that the method of optimization of the operation could reduce the loss. In the meantime, it could ensure the operation safety of the transformer, and prolong the service life of transformer.

The Simulation Study on Transformer Oil-Paper Insulation Polarization Spectrum

Return voltage diagnostic method is an effective method of non-destructive diagnosis in transformer insulating state. The current study is that through experiments get polarization spectrum to analysis the transformer insulating state, but not yet carried out the influence of various factors to the experimental results. So, based on the Debye model and specific parameters comes from one equivalent model of the actual transformer, this paper using RVM methods to simulation analysis maximum return voltage and dominant time constant under different factors. Simulation results show that the diagnostic methods that combine maximum return voltage value with dominant time constant can preferably reflect the transformer insulation state.

Risk-based maintenance for asset management of power transformer: practical experience in Thailand

SUMMARY Nowadays, the requirement on diminishing operating and maintenance costs is highly concerned for utilities in competitive electricity market. Power transformer is first focused due to its acquisition costs and failure consequences (FCs). Traditional preventive maintenance for power transformer is generally applied. However, it is very costly and does not take into account actual transformer condition. Hence, risk-based maintenance is introduced in this paper to facilitate the maintenance works of power transformers. The conditions of power transformers are evaluated from electrical test, insulating oil test and visual inspection by using the ranking and weighting techniques. In addition, the Analytic Hierarchy Process (AHP) is proposed to determine the important weighting factor of each transformer component. The three main criteria of the AHP are maintenance difficulty, FC and failure history. Moreover, the Weibull distribution techniques are applied to analyze failure causes. The computerized web-application program is developed and implemented for practical use in a utility in Thailand. The power transformers installed in 115 kV and 230 kV transmission systems in Thailand are assessed due to availability and quality of data. From statistical analysis of failure records, the conditions of power transformer can be divided into three different zones as risk, moderate and healthy zone. The defective components in risk zone with higher proportion of failure should be carefully focused. The components and overall condition of the transformers are perceived from the analysis of test results. Subsequently, the risk-based maintenance is properly planned according to the actual condition. Therefore, maintenance of power transformer fleet can be effectively managed resulting in higher availability and reliability, lower risk of failure and lower cost of maintenance. Copyright © 2013 John Wiley & Sons, Ltd.

Interleaved winding and suppression of natural frequencies

Ideally, it is desirable to design and manufacture a transformer winding that can render all its internal resonances non-excitable. This study examines the effectiveness of an interleaved winding in achieving this goal. While investigating its effectiveness, it led to the establishment of a much desired theoretical basis that reinforces the reasons put forward in the literature to explain internal insulation failures observed in interleaved windings used in extra high voltage (EHV) transformers. Numerical calculations along with experimental verification on actual transformer windings are presented. This study reveals that most of the natural frequencies that are normally non-excitable in the line and neutral current responses of an interleaved winding have been rendered excitable in the disk-to-disk voltages, thus, providing favourable conditions for insulation overstress because of resonant overvoltages. Prevalence of such a condition is an inherent characteristic of interleaved windings.

Using multiple modes to reconstruct conductor locations in a cylindrical model of a power transformer winding

In the present thesis, we propose and investigate a new approach to diagnose the effects of the various degradation mechanisms, including thermal degradation at hot spots, winding deformations due to the mechanical forces from short circuit currents, partial discharges due to local electric field surges, and increased moisture levels in the cellulose insulation due to decomposition, that affect electric power transformers during their normal operation in an electric power grid.Although the proposed diagnostics method can in principle be used to detect various degradation mechanisms mentioned above, we focus in the present thesis on mechanical deformations of transformer winding structures. Such mechanical deformations are most often caused by mechanical forces from short circuit currents, but they may also be caused by initial manufacturing errors and inconsistencies not detected by the power transformers’ suppliers quality assurance processes.We model a transformer winding surrounded by the transformer-tank wall and the magnetic core as a two-dimensional parallel plate waveguide or as a three-dimensional coaxial waveguide, where one metallic boundary (plate or cylinder) represents the wall of the transformer tank and the other metallic boundary (plate or cylinder) represents the iron core that conducts the magnetic flux. In between there is a set of parallel or coaxial conductors representing the winding segments.The new principle proposed in the present thesis is to insert a number of antennas into a transformer tank to radiate and measure microwave fields interacting with metallic structures and insulation. The responses from the emitted microwave radiation are expected to be sensitive to material properties that reflect the changes caused by any harmful deterioration processes mentioned above. Specifically, we investigate the mechanical deformations of transformer winding structures by determining the locations of the individual winding segments or turns, using measurements of the scattered fields at both ends of the winding structure. We solve the propagation problem using conventional waveguide theory, including mode-matching and cascading techniques.The inverse problem is solved using modified steepest-descent optimization methods. The optimization model is tested by comparing our calculated scattering data with synthetic measurement data generated by the commercial program HFSS.A good agreement is obtained between the calculated and measured positions of winding segments for a number of studied cases, which indicates that the diagnostics method proposed in the present thesis couldbe potentially useful as a basis for the design of a future commercial on-line winding monitoring device. However, further development of the theoretical analysis of a number of typical winding deformations, improvements of the optimization algorithms and a practical study with measurements on an actual power transformer structure are all needed to make an attempt to design a commercial winding monitoring device feasible.

Condition Monitoring of Distribution Transformer's Mechanical Parts Using Sweep Frequency Response Analysis (SFRA)

Distribution transformer is the key element in the electricity transmission throughout the nation. Hence, serious attention for the transformer condition monitoring is a crucial. With an occurrence of short-circuit in the power system, the transformer active parts such as core and winding will experience a mechanical movement created by the electromagnetic forces. There are various types of transformer condition monitoring measurement in market, but the monitoring of the mechanical movement in transformer is still lacking. Therefore, Sweep Frequency Response Analysis (SFRA) has been introduced to assess any mechanical movement especially of the transformer's core and winding. The frequency response of the transformer provides mechanical information of core and winding conditions. The SFRA measurement results were validated using the actual transformer untanking process.

Study on degradation causing components of various characteristics of transformer insulating oil

To operate power transformers long-term, as well as ensuring their insulating reliability, adequate consideration must also be paid to the age-related decline in various insulating oil characteristics. This decline is considered attributable to the generation and increase of trace components in oil over time, which were not present when the oil was new. In this paper, to identify the components causing such degradation, various components detected in actual field aged transformers were added to the base oil to measure a range of characteristics (water content, acidity, interfacial tension, breakdown voltage, dissipation factor, and volume resistivity). The influence of these additives on various characteristics of insulating oil was evaluated to investigate the components responsible for the decline. When organic acids were added, the acidity value declined, as well as a significant decline in volume resistivity for decanoic acid among organic acids. For methyl ethyl ketone, which is a kind of ketones, a degradation of the characteristics was observed in the dissipation factor and volume resistivity, showing the same trend as that in the investigation results of the actual transformer oil. It emerged that phthalate compounds, or those derived from rubber material among the aromatic series, influenced the dissipation factor and volume resistivity in the presence of water. Consequently, the influence of various components detected in actual transformer oil on various characteristics of insulating oil was clarified.

Comparative analysis of linearized systems of anisochronous variable-frequency drives by means of structural models

The wide application of anisochronous variable-frequency driver for machinery in all fields of national economy at present resulted in the unseen before complete block diagram for this type of the drive in the literary sources in the field of study of electric drive. Diagram 1. It is universal, as the parameters of winding of anisochronous motor are not taken into account. Diagram 2. The advantage is the accounting of the parameters of a specific anisochronous machine. In addition, the version with the PID loop of speed corresponds completely to the definition of the actual frequency transformers and provides high accuracy of development of the required speed diagram. The comparative disadvantage is small overshoots in the moment curve. If these overshoots do not exceed permissible limits, such diagram may be considered as the basic one. Diagram 3. Corresponds to the classic scheme of the systems with subordinate control and has the best dynamic indices regardless of the speed regulator type. If the results are to be used in practice, one should take into account, that the frequency transformer with the PID loop is commonly used as the transformers with the finished system of subordinate control are made in small number.

Experimental Investigation on Model Transformer Windings to Analyze Axial and Radial Displacements

Sweep Frequency Response Analysis (SFRA) method is an effi cient method for predicting the geometric changes, and research on the optimum and unambiguous application is still in progress. In order to correlate integrity of transformer windings with changes in the frequency responses, a lot of measurements have to be performed and analyzed. The present work discusses special experimental investigations carried out on model transformer winding to study the various aspects of axial and radial winding displacements using SFRA test. The experimental results for axial and radial winding displacements are presented and analyzed. The analysis will help in understanding the health of an actual transformer and diagnosing it for any impending fault with respect to winding movements.