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Since the internal turn-to-turn faults (TTFs), as a common cause of the transformer failures, result in minor changes on terminal currents/voltages, they maybe undetected by the conventional protective relays. In this study, a simple, sensitive and robust linkage flux-based technique is proposed to protect the power transformers against TTFs. In this approach, some separated multi-turn windings as search coils (SCs) have to be wrapped around the transformer core legs to sense the related passing flux. Since passing equal flux through a transformer core leg in normal condition induces equal voltages in the related SCs, variation of the induced voltages indicates the fault occurrence in that phase. Against the traditional differential protection schemes, current transformer error and saturation, tap changer operation, energising inrush current, over-fluxing etc. cannot impact the proposed technique performance. Therefore, it can be introduced as a comprehensive protection technique for power transformers.To confirm the proposed technique performance, it is tested on a real 50 kVA, 20 kV/400 V three-phase distribution transformer, in various conditions, too.

The aim of this paper is to present a new procedure for the electromagnetic analysis of a measuring current transformer under sinusoidal conditions in its electrical and magnetic circuit. The influence of the magnetic hysteresis has been taken into account using the measured inverse magnetization curve and phase lag between the time waveforms of the magnetic field and the magnetic induction. Using the proposed analysis, ratio and phase errors of the current transformer have been calculated. The results of the calculation have been compared with experimental results and a good agreement has been found.

Hydropneumatic transformer (short for HP transformer) is used to pump pressurized hydraulic oil. Whereas, due to its insufficient usage of energy and low efficiency, a new kind of HP transformer: EEUHP transformer (Expansion energy used hydropneumatic transformer) was proposed. To illustrate the characteristics of the EEUHP transformer, a mathematical model was built. To verify the mathematical model, an experimental prototype was setup and studied. Through simulation and experimental study on the EEUHP transformer, the influence of five key parameters on the output flow of the EEUHP transformer were obtained, and some conclusions can be drawn. Firstly, the mathematical model was proved to be valid. Furthermore, the EEUHP transformer costs fewer of compressed air than the normal HP transformer when the output flow of the two kinds of transformers are almost same. Moreover, with an increase in the output pressure, the output flow decreases sharply. Finally, with an increase in the effective area of hydraulic output port, the output flow increases distinctly. This research can be referred to in the performance and design optimization of the EEUHP transformers.

Digital relays are capable of computing the negative-sequence current on both primary and secondary sides of the transformer along with the phase difference between these two negative-sequence currents. By using both phase and magnitude information, negative-sequence current could be used to detect minor turn-to-turn faults involving 3% of the transformer's windings or more. Turn-to-turn faults may still occur even if no current is flowing on one side of the transformer, such as during energization. With no current flowing in the secondary windings of the transformer, negative-sequence current-based algorithms become insensitive. This paper introduces a relay prototype, using both negative-sequence current and negative-sequence voltage, which retains its sensitivity during energization. The relay's performance for several commonly encountered system scenarios, such as overexcitation, current-transformer saturation, nonzero fault resistance, transformer energization, and external faults were also examined. The experimental results presented in this paper indicate that the algorithm proposed in this paper is faster and more sensitive than restrained current differential protection and is capable of detecting turn-to-turn faults occurring during transformer energization.

Frequency response analysis (FRA) has been globally accepted as a reliable tool to detect mechanical deformation within power transformers. However, because of its reliance on graphical analysis, interpretation of FRA signature is still a challenging area that calls for skilled personnel, as so far, there is no widely accepted reliable standard code for FRA signature identification and quantification. While several papers investigating the impact of various mechanical winding deformations on the transformer FRA signature can be found in the literature, no attention was given to investigate the impact of various bushing faults and transformer oil degradation on the FRA signature. This paper introduces a detailed simulation and practical analyses to elaborate the impact of bushing faults as well as transformer oil degradation on the transformer FRA signature. In this regard, the physical geometrical dimension of a three phase power transformer is simulated using 3D finite element analysis to emulate the real transformer operation. Various bushing faults have been emulated on the studied model and oil degradation is implemented through changing oil permittivity. Practical FRA test is conducted on a three phase 132 kV, 35 MVA power transformer to validate the simulation results. Results show that bushing faults and oil degradation can be visibly detected through FRA signature.

A new type of ring-type piezoelectric ceramic transformer consisting of two concentric piezoelectric ceramic rings polarized axially and radially is analyzed. When the electric load impedance is considered, the electromechanical characteristics of the piezoelectric transformer are studied. The dependency of the voltage gain, the efficiency (the ratio of the output over the input power) and the effective electromechanical coupling coefficient of the piezoelectric transformer on the geometrical dimensions are analyzed. Meanwhile, the load dependency of the electromechanical parameters of the transformer is also investigated. It is concluded that the electromechanical characteristics of the piezoelectric transformer are closely related with the geometrical dimensions and the load electrical impedance. The conclusions can be used for the optimization design of the ring-type piezoelectric ceramic transformers in the engineering applications.

Saturation is a condition in which the magnets are fully transformer cores and generate maximum magnetic flux. Some parts affect the resilience and create distortions that can harm the heart. Core saturation can also increase the temperature and magnetization current transformer. In this study, we proposed a measurement method to obtain the necessary parameters to calculate a reliable indicator of the state of the transformer core saturation. The main effects of nonlinear flow in the transformer core are saturation, eddy current and hysteresis. In saturation, the core transformer is as a source of generating harmonic currents, some of which will flow directly to the primary and secondary windings. The method is based on the magnetization current, the phenomenon of harmonics and power factor is evaluated by measuring the no-load current at three-phase transformer, with a high magnetic flux density imposed. Measurements were taken at each phase of the transformer core. The transformer is connected to a variable voltage variable frequency (VVVF) as a voltage source and the investigation carried out at various flux densities. The results showed that the magnetization current and harmonic phenomena increased significantly when the high magnetic flux density and vice versa injected with power factor declined sharply. This phenomenon can be used as an indication of saturation of the 3-phase transformer core.

This paper presents the design of electrode for PD-location simulation in oil insulated power transformer and the application of Acoustic Emission (AE) method. The purpose of this design is to make a simple PD signal simulation and to save the time of experiment. The design must take into account the electric field stress at the electrodes (anode) that will cause PD. The electrodes were designed as 2 types. The first is a conventional electrode expected to make a high nonuniform field. The second electrode was designed as insulation layer and transformer coil to generate higher nonuniform field and expected to cause PD easily. Electrodes were simulated to determine the maximum of electric field by installing in the transformer model. Then, the electrodes are installed in the transformer model to make the real test by supplying high voltage to the electrodes to generate PD signal. From the measurement results of PD-location in the power transformer model according to AE and TDOA method found that, the first electrode has uncertain PD-location measurement results. Moreover, it take so long time of any experiment to obtain PD-signal and sometimes become critical breakdown as a result to damage measurement device. While the PD-location detection results from the second electrode found that it can be easily simulated PD signal. The PD-location result has a better precision or has statistical data to detect PD-location explicitly. Therefore, this special designed electrode could be applied for PD detection study in power transformer or other electrical equipment as well.

Winding faults are one of the major causes for failures in Power transformer. Detection and localization of winding faults is indispensable for prevention of damages as the outage may lead to costly, time consuming repair and replacement of the equipment. This contribution is aimed at locating inter disc faults using the sweep frequency responses of the winding. A method for determining the location of faults using the Fault Factor characteristics has been developed using a 22 kV continuous disc winding. The proposed methodology employing the hyperbolic model predicts the exact location of the fault by considering only two known reference values, for different percentage of faults. The algorithm is validated on interleaved and layer winding of different ratings. Using circuit simulation package, verification is done on a high voltage winding of a 25MVA 230/6.6kV transformer, with the low frequency equivalent circuit model of the transformer winding.

In this paper, achieved rise temperature distribution about degradation phenomenon of 24 MVA distribution cast resin transformer using CFD(Computational Fluid Dynamics). Usually, life of transformer is depended on temperature distribution of specification region than thermal special quality of transformer interior. Specially, life of transformer by decline of dielectric strength decreases rapidly in case rise by strangeness transformer interior hot spot temperature value permits. Because calculating high-voltage(HV) winding and low-voltage(LV) winding of cast resin transformer and Joule's loss of core for improvement these life, forecasted heat source, and HV winding and LV winding of cast transformer rise temperature distribution of core for supply of electric power and temperature distribution of highest point on the basis of the results. Also, calculated temperature rise limit of cast resin transformer and permission maximum temperature using analysis by electromagnetic heat source. Calculated and forecasted rise temperature distribution by heat source of thermal analysis with calculated result.

Identification of winding insulation failure during lightning impulse testing of transformer has been an important issue over a long period of time. It requires a significant human expertise and knowledge for proper judgment of transformer insulation. In this paper, the bivariate dependent rate analyses are proposed to identify the failure in transformer windings. The proposed analyses enable the calculation of winding response due to any impulse voltage excitation of full wave (FW) and chopped wave impulse (CW) for typical transformers. Initially, the line of best-fit on the scatter diagram is utilized to visualize the similarities between the measured winding responses and also to identify the type of relationship with potential outliers. Further, ellipse analysis is utilized to calculate the diversification (size, shape and orientation) between the responses. The actual interdependency between winding responses is established through nonlinear interpretation coefficients. To prove the feasibility of the analyses, 66.7 MVA, 90 MVA, 150 MVA, 250 MVA transformers, 80 MVAr reactor and 22 kV interleaved winding are used.

The current transformer (CT) saturation phenomenon has been one of the main problems for the power transformer differential protection, leading to incorrect current measurements and relay misoperation. This paper proposes a fast and efficient transformer differential protection scheme with additional differential CT saturation and cross-country fault detection modules after the external fault detection, all of them based on the differential wavelet coefficient energy with border distortions in order to stabilize the relay during external faults and distinguish accurately CT saturation from cross-country internal faults. The proposed method was assessed by using representative simulations of internal faults, transformer energizations, and external faults with CT saturation followed by cross-country internal faults, and good results were achieved.

Aiming at the control problem of the servo control system of electromechanical actuators (EMA), this paper designs a digital controller for EMA. Strategy that combines the traditional feedback control with position feedforward control and the three-closed-loop control is in used, including LVDT position loop, RVDT velocity loop and the current loop. This strategy improves the response speed, tracking accuracy and anti-interference capability of the system. This paper uses LabWindows/CVI to design a control interface based on CAN communication, which is used to simulate the flight control computer. Finally, the experiments of the system tracking response and tracking response of the brushless DC motor are completed, they verify the rationality and reliability of the design.

This paper presents different methods to determine the parameters for the equivalent electrical circuit model of a high-frequency planar transformer. The first method is implemented in the circuit simulation software utilizing a 1-D electromagnetic analysis. The second method uses a 3-D electromagnetic analysis and is implemented in a finite-element analysis software. The third method is a differential evolution (DE)-based algorithm using the experimental transformer data. The first two methods are useful in the design stage to predict the performance of a planar transformer, while the third one can be applied to validate the design. The performance and accuracy of the three methods are assessed by comparing each method’s parameter estimate of an actual planar transformer. The comparison showed that the predictions of magnetizing inductance by the two numerical analyses are accurate and comparable with that of the DE-based estimation method. However, the series resistance and leakage inductance determined by the DE algorithm tend to be higher, as predicted by the two numerical methods, due to the nonconsideration of the measuring leads impedance in the numerical models.

This paper presents the reduction of noise and vibration concerning the magnetostriction effects for a single-phase power transformer with a large capacity of 200 MVA. Two magnetic core shapes are investigated: 1) D-yoked core and 2) square-yoked core. The D-yoked core is used for the construction of the transformer prototype in this paper. The magnetostriction and the hysteresis loop of the core material are measured for the simulation and analysis of noise and vibration. The transformer prototype is assembled with an external clamping force applied on the core, and the core vibration and sound-level are observed. The transformer operates with a periodic excitation that may induce resonance in the core. To avoid this, a finite-element analysis is used for modal analysis to identify the natural frequencies of the core. A tank is also designed with a sufficiently rigid structure to avoid resonances. The sound-level of the fully assembled transformer prototype is measured, and it is found to have a low-noise level below 65 dB.

Transformer is widely used element on power system and industrial area. Especially the transformers installed at power system are exposed to an environment of arbitrary changed. Thus the prediction of degradation and the analysis of response to impulse are important. To conduct those works, the electrical characteristics of system should be analyzed, effectively. But the analysis of electrical characteristic in electric machine level such as pole and pad-mounted transformer is almost no, thus commercial VNA (Vector Network Analyzer) is used to getting the response in wide frequency range. However, the output power of VNA is usually under 10mW, so verification for effectiveness of measuring electrically large component should be conducted, firstly. Next, after getting total S-parameter of transformer, predicting impulse response can be performed in time-domain with circuit simulator. In this paper, it is introduced that verification effectiveness of VNA using transfer function from SFRA (Sweep Frequency Response Analyzer), firstly. Next, total S-parameter, six by six matix form, was built using measured 2 port S-parameter from vector network analyzer. To get the response to impulse which is defined by IEC 60060-1, time-domain simulation is conducted to ADS (Advenced Design System) circuit simulator.

In this article, novel methods and ideas are introduced, which altogether lead to an accurate model of power transformer windings. First, by the determination of non-dominant (hidden) resonances from frequency-response tests, a ladder model is proposed. Next, it is improved by assigning different values for similar elements of each section of the model. The parameters are obtained by minimizing the error function via a genetic algorithm. Sensitivity analysis is then applied to the obtained model to achieve further examinations and tests. Measurements have been driven from the windings of a 20/0.4-kV, 1600-kVA transformer. Modeling, methodologies, and sensitivity analysis in this article can be very useful for future research aiming to find internal faults of the transformer with the frequency response analysis.

In this paper the mass flow distribution in zig-zag cooled power transformer windings is shown to play a crucial factor to accurately predict the winding temperature. In order to enable thermo-hydraulic network models for transformer design, new correlations are derived for combining and dividing T-junctions and elbow configurations. Good correspondence is achieved in comparison with CFD simulation results for a zig-zag cooled power transformer winding.

Early detection and localisation of winding faults within the transformer can help make preventive actions and reduce potential damages to the transformer and the power system. This research work presents a new technique for sensitive detection and localisation of shorted turns on the windings of power transformers throughout low-frequency response measurements of the transformer windings. To this end, using genetic algorithm, the detailed model of the damaged winding by the fault is estimated from the measured low-frequency response data up to 10 kHz. The fault is localised along the winding by establishing the differences between the transfer functions of the healthy and faulty state of the winding units using statistical indicators. The experimental measurements which were made on a test transformer damaged by a low-level short-circuit fault proved that the newly developed method is sufficiently able and sensitive to detect and localise failures of only few shorted turns on the transformer windings.

The article examines the methods of calculating capacitive currents in a measuring transformer based on a resistive voltage divider. The developed methods may be used to optimize the design of resistive dividers.

This paper presents a symmetrical components approach for computing the phase-coordinates nodal admittance matrices of three-phase transformers, where each connection is comprised either of three single-phase units or one three-phase unit. The approach is based on assembling the symmetrical component circuits into the different three-phase connections; it can straightforwardly handle unsymmetrical transformer banks with different phase electrical characteristics or missing phases, and grounding impedances. The proposed approach easily accounts for the various clock numbers quoted in the British Standard (BS) and the International Electrotechnical Commission (IEC) Standard on power transformers; this presents an advantage as compared to classical phase-coordinates approaches that require defining a distinct connection matrix corresponding to each transformer vector group.

In this paper, a new type of power electronic distribution transformer (PET) has been introduced based on the power electronics converter on the primary and secondary sides of the transformer. This PET has three stages and the input stage has a three-level, three-phase rectifier. The middle stage has two three-level single-phase converters and a high-frequency transformer; and, the output stage is a three-phase, two-level inverter. This power electronic distribution transformer provides many advantages, such as power factor improvement, reactive power compensation, eliminating harmonics, and controlling and protecting itself (PET) with minimum size, compared to the traditional transformer. The MATLAB/Simulink was used to analyze and validate the power electronic distribution transformer.

This paper presents the design and analysis of a novel three-phase rotary transformer that can be used to replace the brushes and slip rings of doubly fed induction generators. The transformer core is designed for easy assembly and to ensure a relatively constant reluctance while the secondary of the transformer is rotating. Guidelines for the air-gap size, stator and rotor core shape, and excitation current values are derived to ensure a balanced three-phase magnetic flux in the transformer core. The expression of the magnetizing coupling coefficient is developed with the introduction of different types of flux tubes. Guidelines and references for optimum design were provided.

An analysis of the interleaving effect for the secondary winding distribution of a toroidal transformer is presented in this paper. The equations to calculate the leakage inductance of the toroidal transformer are derived using MMF diagrams for the different secondary winding distributions. The simulation and experimental results are provided to show the validity of the theoretical calculation.

Modern electric-powered vehicles include several sources and loads. This paper extends the idea of introducing multiple sources and loads into an onboard vehicular integrated power system. The proposed power conditioning system is formed around a multiwinding integrated transformer. Both inductive and capacitive elements of this magnetic component affect the power conditioning stages of the system. This paper proposes an experimental transformer modeling procedure that includes the inductive and capacitive parameters. A mathematical procedure is developed, simplifying this more detailed experimental model of the multiwinding transformer into a $\Pi\ RLC$ circuit that can be utilized in the system transient analysis. The modeling method is applied to a three-winding transformer and is verified through simulations and experiments.

The interests in multiphase (more than three) system are escalating recently especially in the motor drive applications. Thus, this paper introduces the graphical phasor diagram method in designing the multiphase transformer connection. The proposed method eases the design process of the static multiphase transformer that produces multiphase output from the standard three phase input. The transformer connection was simulated in ANSYS Maxwell and the multiphase waveform with appropriate phase angle was obtained. The design of five-phase transformer using graphical phasor and simulation results from the finite elements software are presented in this paper.

Power transformer is one of the major and key apparatus in electric power system. Monitoring and diagnosis of transformer fault is necessary for improving the life period of transformer. The failures caused by short circuits are one of the causes of transformer outages. The short circuit currents induce excessive forces in the transformer windings which result in winding deformation affecting the mechanical and electrical characteristics of the winding. In the present work, a transformer producing only the radial flux under short circuit is considered. The corresponding axial displacement profile of the windings is computed using Finite Element Method based transient structural analysis and thus obtained displacements are compared with the experimental result. The change in inter disc capacitance and mutual inductance of the deformed windings due to different short circuit currents are computed using Finite Element Method based field analyses and the corresponding Sweep Frequency Responses are computed using the modified electrical equivalent circuit. From the change in the first resonant frequency, the winding movement can be quantified which will be useful for estimating the mechanical withstand capability of the winding for different short circuit currents in the design stage itself.

Modern methods of braking digital differential protections of block transformers when there are external short circuits are considered. The effect on the braked quantities of such factors as the phase difference between the side currents, and also saturation of the current transformers is described.

Welding is a materials-joining process that produces coalescence of materials by heating them to the welding temperature with or without the application of pressure or by the application of pressure alone, and with or without filler metal. It is used to make welds. It is observed that the welding transformer with choke or movable core is having large size, so to reduce the size we are replacing the choke with one coil. This coil functions same as the choke. This coil helps to reduce the size as well as the cost of the welding transformer. The forced air cooled transformer consists of an exhaust fan which rotates at a constant speed whether the welding work is going or not. So, the more energy will be wasted there. To avoid this, the load series motor is used. The load series motor as the name suggests is a motor, which is to be connected in series with a load. The load series motor, which shaded pole motor but designed in such a way that if connected in series with load, it will run and speed of such motor will be proportional to the load current. The ordinary exhaust fan motor can be, easily replaced by the load series motor.

This paper presents two algorithms for the creation of an analytical model of a single-phase transformer-based inverter, using either the measurements of the control frequency-dependent characteristics of the inverter or the initial in-circuit frequency-dependent measurements of the transformer. The paper discusses how the parameters of the line transformer influence the dynamic properties of the inverter and, as a consequence, the design of the instantaneous control feedback loop. Line transformers, widely used in industry, have not yet been analysed for use at higher than normal operating frequencies. The basic parameters of the transformer are the nonlinear functions of the primary voltage amplitude and frequency. The paper includes verification of both methods using the breadboard experimental model. In the final step, the inverter control transfer functions are calculated. To show the utility of both models, an exemplary discrete controller for the experimental inverter model has been designed and tested. Copyright © 2015 John Wiley & Sons, Ltd.

The clamping of the power transformer magnetic circuit allows maintaining the sheet stack and provides an additional mechanical rigidity. It has consequences on the acoustic noise of transformers as the magnetic cores of power transformers vibrate because of the magnetostriction and, if the corners are considered, Maxwell’s forces. The indirect impact of a lack of clamping on the core losses is studied, especially on the interlaminar air gaps in the corners. In this paper, it is shown numerically with finite element modeling and experimentally with a specific testbench that induced vibrations can change the flux distribution and thus the losses.

This paper designed a 3/12 phase circular phase shifting transformer applied to multi-pulse rectifier. The transformer is built by using rotating magnetic field principle, and the ferromagnetic structure is similar to an induction motor. Compared with the general column iron core phase shifting transformer, the circular phase shifting transformer has the advantages of compact structure, more symmetric magnetic circuit, and the design of primary and secondary winding is more simple. This paper established the mathematical model of the circular shifting transformer, the voltage equations are derived. Then analysis the inhibitory effect of harmonic wave in 24 pulse rectifier. Verify the feasibility of the circular phase shifting transformer through the experiment, when the circular phase shifting transformer is applied to multi-pulse rectifier, it is effective to suppress the harmonic wave of the Power grid.

In design of a pulse transformer, there are several conflicting objective functions that should be optimized. However, due to the high complexity, the conventional design methods cannot consider all of them simultaneously. In this paper, multiobjective particle swarm optimization is used to design a pulse transformer. This method is based on Pareto optimality. The output consists of a set of optimal solutions that the best design is selected from it. To use this optimization method, a model is developed for a pulse transformer with toroidal wound core. The model considers magnetic, electric, and thermal characteristic of a transformer. Its simple calculations make it proper for using in an optimization process. A transformer is designed and implemented for minimum rise time, temperature rise, and volume using the presented method. This transformer is compared with a transformer that has been designed by conventional methods. Measurements and comparisons show that the results are more acceptable than the results of convectional designs besides simplicity and accuracy of the method.

This paper describes the application of the finite-elements method for determining the distribution of losses over windings and a detailed thermal-hydraulic network model for determining the value of the hot-spot factor and the hot-spot temperature. The influence of nonuniform losses in the conductor of the windings and the influence of nonuniform cooling are clearly separated. A detailed discussion of the components included in the hot-spot factor is given in this paper, enabling proper understanding of this complex and important quantity. The case study transformer was a 100-MVA oil power transformer with oil-directed water-forced cooling. The method was applied within the scope of the project of increasing the power of a hydro power station by 12%. The task was to calculate the temperatures and to recommend whether the reconstruction of the transformer is necessary. The developed calculation method and software were hitherto used for transformer design (in the production or the reconstruction stage of transformers) and it is the first application to give an answer as to whether it is possible to increase the power of an existing transformer. In this specific application, necessary onsite measurements for determining the characteristics of the coolers were performed.

Frequency response analysis (FRA) is proven to be a powerful tool to detect winding deformation within power transformers. Although the FRA test along with the equipment are well developed, interpretation of FRA signature is still a challenge and it needs skilled personnel to identify and quantify the fault type if exists as at this stage, there is no reliable standard code for FRA signature classification and quantification. As it is very hard to implement faults on physical transformer without damaging it, researchers investigated the impact of various mechanical winding deformations on the transformer FRA signature by randomly changing the value of particular electrical parameters of the transformer equivalent electrical circuit. None of them however, precisely investigated the correlation between physical fault level and the percentage change in each parameter. In this paper, the physical geometrical dimension of a singlephase transformer is simulated using 3D finite element analysis to emulate the real transformer operation. A physical radial deformation of different fault levels is simulated on both low voltage and high voltage windings. The impact of each fault level on the electrical parameters of the equivalent circuit is investigated and the correlation between the fault level and the percentage change in each parameter of the equivalent circuit is provided. This will facilitate precise fault simulation using transformer equivalent electrical circuit and ease the quantification analysis of FRA signature.

Based on an enhanced topological representation of the transformer core, flux air paths, and tank, a duality-based transformer model is proposed for low and mid-frequency transients analysis. In the developed transformer model, the core and tank iron are represented based on a frequency-dependent hysteresis model. The winding capacitances and the frequency dependency of the winding resistance are also incorporated in the developed model. Furthermore, a detailed model is developed for the air gap and tank, and the corresponding average equivalent is presented which is more appropriate for extracting the parameters from the measurement. In addition, the nonuniform air gap and the fringing flux effects are taken into account, and an approach is presented to obtain the corresponding parameters. The developed models also include the equivalents of the tank magnetic shield and the structural parts. Part II of this paper provides validations and further simulation results.

Frequency response analysis (FRA) has become a widely accepted tool to detect power transformer winding deformation due to the development of FRA test equipment. Because FRA relies on graphical analysis, interpretation of its signature is a very specialized area that calls for skilled personnel, as so far, there is no reliable standard code for FRA signature identification and quantification. Many researchers investigated the impact of various mechanical winding deformations on the transformer FRA signature using simulation analysis by altering particular electrical parameters of the transformer equivalent electrical circuit. None of them however, investigated the impact of various physical fault levels on the corresponding change in the equivalent circuit parameters. In this paper, the physical geometrical dimension of a single-phase transformer is simulated using 3D finite element analysis to emulate the real transformer operation. A physical axial displacement of different fault levels is simulated in both low voltage and high voltage windings. The impact of each fault level on the electrical parameters of the equivalent circuit is investigated. A key contribution of this paper is the charts it introduces to correlate various axial displacement levels with the percentage change of all transformer equivalent circuit parameters due to the axial displacement fault. In contrary with other researchers who only considered mutual inductance between low voltage and high voltage windings, simulation results shown in this paper reveal that other circuit parameters should be changed by a particular percentage to accurately simulate particular fault level of transformer winding axial displacement. Results of this paper aid to precisely simulating winding axial displacement using transformer equivalent circuit that facilitates accurate qualitative and quantitative analysis of transformer FRA signatures.

The transformer model developed in Part I is validated based on the zero-sequence test data, a ferroresonance event, and the geomagnetically induced current (GIC) measurements. Various transformer core constructions, including single phase, three limb, five limb, conventional shell type, and seven-limb shell type are represented, based on the proposed transformer model. The simulation results show high accuracy of the proposed transformer model in representing the studied cases. The study reveals that the saturation of the transformers at a given GIC level is more severe than that predicted by the existing transformer models. Furthermore, the proposed transformer model clearly explains the reasons for the previously reported discrepancies between the GIC experimental and simulation results. The study also concludes that for an accurate transformer model, particularly for the three-limb core type, the detailed representation of the zero-sequence characteristic is an essential requirement. Such a characteristic can be obtained based on either the proposed approach of the paper or a zero-sequence dc excitation test in addition to the test data at the power frequency.

The paper deals with very fast transient phenomena in a system consisting of two parts: a cable line and a transformer winding. In this case an adequate model should be considered as a circuit with distributed parameters. Its description is given by a system of partial differential equations of hyperbolic type. Our approach is based on a numerical solution in the time domain and the method FDTD has been used. It allows obtaining results in a form of time-space voltage and current wave distribution along the cable line and the transformer winding. This distribution is depending on many factors some of them were studied in this paper.

Transformer tank vibration has been used for the condition monitoring and fault diagnosis of power transformers, as well as for the evaluation of radiated sound power from such power transformers. In both applications, seeking a correlation between transformer tank vibration and the vibration of the transformer windings and core becomes a challenge for fault identification and noise control at the sources of vibration and noise. The purpose of this paper is to experimentally investigate the winding vibration of an electrically live power transformer and characterize the changes in the spatial and frequency features of the vibration as various mechanical faults are introduced to the transformer winding. To avoid the effects of transducer loading and electromagnetic fields on the measurement results, a laser Doppler vibrometer was used to make non-contact measurements of the winding vibration.

Transformer winding deformation is one of the main types of transformer faults. To check if a power transformer is being under winding deformation, the transformer can be connected in a current transformer during its testing. A transformer winding simulating model is set up under this connecting manner. Then the simulation has been performed with current source which is the frequency sweep power. The simulation results show that the winding deformation can be reflected effectively with current source method. This method lays the foundation for the realization of on-line monitoring and diagnosis of the transformer neutral directly grounded side winding.

Medium voltage in the electric power system of ship typically is powered by a large capacity transformer for low voltage electrical apparatus. When switching on, the primary side of transformer will produce very large current, which would endanger the safe operation of power for ships. The mechanism and characteristics of magnetizing inrush current is analyzed when the transformer switches with no load. We think that the reason caused magnetizing inrush current is transformers saturation. Pre-excitation is presented through a small volume transformer magnetizing method of suppressing the inrush current of transformer and validated by simulation and experiment.

Power systems as 10kV, 35kV and etc have a lot of high-voltage three-phase three-element combined transformer. At present, all of the combined transformers are verified according to single-phase verification method, but the results can’t reflect the true error characteristics of combined transformer. So, it is suggested to adopt three-phase verification method to verify combined transformer. However, when combined transformer is verified according to three-phase verification method, it has not been clear yet that what influence magnetic field generated by current has on voltage error. In this paper, through voltage error test on combined transformer with three-phase verification method at different current, it is discovered that magnetic field has a larger influence on voltage error in the presence of a magnetic field, with the increase of voltage, the influence of magnetic field on voltage error decreased gradually from larger values. The use of three-phase verification method and appropriate modification of current error limits are recommended when combined transformer is verified.

Transient saturation characteristics of TPY-type current transformer have great impact on the right action of line differential protection. This paper proposes an analytical method of line differential protection under current transformer saturation by utilizing current transformer model and test methods. The true current value of primary side can be obtained by our proposed method and therefore it yields correct assessment of line operating status. This method has high reliability applying to practical engineering examples of differential protection.