Single-phase Power Transformer Research Articles

Study of Problem and Effect Mitigation Technique of Unbalance Capacitance in 500 kV Single Phase Transformers

This article presents the study of the effect of unbalanced stray capacitance in single-phase 500 kV power transformers and establishes the mitigation technique. The power transformers were operated in Wang Noi Substation for transmitting the electrical power. There are 3 units of single-phase power transformer. Previously, a transformer of phase B failed after being serviced for several years. Thus, the new power transformer was ordered instead of the failed one. However, once the new system had been operated, the hotspots at the surge arrester of tertiary winding (22 kV) were found and the unbalance of phase voltages was observed, resulting in overvoltage as a root cause of the problem. Once a thorough investigation was done, it was found that there was an effect of unbalanced stray capacitance between tertiary winding and ground core since the new power transformer has some different designs compared with the remaining. Hence, the mitigation technique was performed by adding the capacitor parallel to the tertiary winding until the voltage balance was achieved. Simulation with the PSCAD program was performed to determine the optimum value for additional capacitors, i.e., voltage balance, using an iterative method. In this article, the capacitors used for additional were capacitor voltage transformers, which have been installed. As a result of the troubleshooting, the voltage at the 22 kV bus was more balanced as well as not causing overvoltage, and the hotspots at the surge arrester of tertiary winding were not detected resulting in gaining the stability and reliability of using these transformers.

Power transformer fault diagnosis using dynamic multiscale graph modeling and M2SGCN network based on statistical fusion

Power equipment fault diagnostics hold significant importance for the stability of power grid systems. In pursuit of this objective, this paper proposes a fault diagnosis method that utilizes dynamic multiscale graph (DMG) modeling and the multiscale multi-stream GCN(M2SGCN) network, incorporating statistical fusion. Specifically, a novel DMG modeling method is proposed to derive visibility graph data and horizontal visibility graph data from vibration signals across multiple scales. Next, a comprehensive neural network architecture named M2SGCN is established to learn global and local features simultaneously, providing a more precise representation. Subsequently, a Dempster Shafer evidence theory statistical fusion technique combined with an adaptive threshold model (DSTFusion) is utilized to integrate primary decision results for enhanced fault diagnosis accuracy. In addition, two datasets obtained from single-phase and three-phase power transformers are analyzed to demonstrate the evolution process. When compared to state-of-the-art indicators such as accuracy, precision, recall, and F1 scores, the method proposed excels in multiple aspects, successfully detecting fault states before their occurrence and achieving outstanding performance.

An Experimental Set-up Involving Low-cost Digital Controller to Study the Magnetizing Inrush Current in a Transformer using Point-on-Wave Switching Technique

Abstract Generally in under-graduate studies, magnetizing inrush current (MIC) is discussed theoretically without giving much practical exposure. This paper presents the development of a low cost experimental set-up using a digital controller to study the MIC and the different parameters which can affect the same. This also helps to show how the inrush current can be minimized. This set-up also provides a hands-on experience of MIC and its control in under-graduate study, which can help an upcoming practitioner in industry as well as in further research. This paper presents a brief description of MIC, followed by a short analysis. Here, a pair of anti-parallel thyristors are connected in series with the primary winding of a single-phase power transformer. The turningon instant of this switch, with respect to the zero-crossing instant of the input supply voltage, may be adjusted through a firmware, in a PIC18F4620 from Microchip Technology microcontroller development board from Microchip Technology to control the transformer energisation instant. The firmware is developed in MPLABX-IDE from Microchip Technology, and the scheme is verified via simulations in Proteus simulation software. A suitable circuit to support the microcontroller development board to achieve the above function is designed and fabricated.

Estimation of the Equivalent Circuit Parameters in Transformers Using Evolutionary Algorithms

The conventional methods of parameter estimation in transformers, such as the open-circuit and short-circuit tests, are not always available, especially when the transformer is already in operation and its disconnection is impossible. Therefore, alternative (non-interruptive) methods of parameter estimation have become of great importance. In this work, no-interruption, transformer equivalent circuit parameter estimation is presented using the following metaheuristic optimization methods: the genetic algorithm (GA), particle swarm optimization (PSO) and the gravitational search algorithm (GSA). These algorithms provide a maximum average error of 12%, which is twice as better as results found in the literature for estimation of the equivalent circuit parameters in transformers at a frequency of 50 Hz. This demonstrates that the proposed GA, PSO and GSA metaheuristic optimization methods can be applied to estimate the equivalent circuit parameters of single-phase distribution and power transformers with a reasonable degree of accuracy.

Effect of ferrofluid magnetization on transformer temperature rise

In electrical engineering, the heat transfer can be enhanced by changing the thermophysical properties of insulating oils. In this paper, a single-phase power transformer with a nominal power of 5 kVA is subjected to a temperature rise test with three different transformer liquids. The first test is carried out with a novel gas-to-liquid transformer oil applied as a cooling and insulating medium. The other tests are conducted with ferrofluids based on this oil and MnZn ferrite nanoparticles of a low and a high nanoparticle concentration. The ferrofluids are characterized by magnetization curves, magnetic susceptibility and temperature-dependent magnetization measurements. The nanoparticle size distribution is determined from dynamic light scattering and the magnetization data. From the temperature rise profiles of the transformer at various inner locations, it has been found that the low-concentrated ferrofluid significantly reduces the transformer temperature rise. The enhanced cooling performance is ascribed to the thermomagnetic and natural convection, and increased thermal conductivity. The application of the ferrofluid with the high nanoparticle concentration resulted in a remarkable increase of the transformer temperature rise. The deteriorative cooling effect is attributed to the hindered natural and thermomagnetic convection due to the high ferrofluid magnetization and strong magnetic interaction of the ferrofluid with the magnetic field near the transformer core.

Investigation of the Effects of DC Bias on Single-Phase Shell Type Transformers Using Frequency-Dependent Reluctance-Based Model

In this article, a reluctance-based model is developed for time-efficient analysis of shell type single-phase power transformers under the direct current (dc) bias conditions. Unlike other reluctance-based transformer models in the literature, the developed one considers frequency dependent nature of the winding resistances. This is important especially for accurate determination of losses and maximum loading capability (MLC) of the transformers under dc bias and non-sinusoidal conditions. In addition to that, by using the developed model, three different MLC determination approaches, which are based on the rated primary side current, rated total loss and rated primary winding loss, are examined for dc bias conditions. These novel examination results clearly point out that among three approaches the rated primary winding loss-based one should be preferred for the safe operation of the transformers in the systems with dc bias.

Experimental Investigations of Magnetizing Inrush Current in Power Transformer Using a Proposed Synchronous Switch.(Dept.E)

This paper introduces deep and carful theoretical and experimental investigations of the magnetizing inrush current (M.I.C.) phenomenon in single phase power transformers, All salient parameters influencing M.I.C. waveform and particushed by the control of the instant of switching the supply to the transformer, the factor which appreciably affects M.I.C.

Voltage - Current Waveforms Of Single-phase Power Transformer Due To DC Bias

The exist of direct current (DC) component in an alternating current (AC), known as DC bias (or DC Off-set) has undesirable effects, particularly on the power transformer, due to the problem of core saturation (half-cycle saturation). An investigation of magnetizing current waveforms of single-phase power transformer due to DC bias injection through MATLAB simulation is present in this paper. The simulation and study are done by injected AC and DC currents simultaneously. The value of AC is fixed and DC is adjusted (variable) in magnitude and also in the directions (positive and negative). The results show that the waveforms (displayed in magnetic flux) are distorted when the DC bias exists. The pulsated waveforms are pushed to half-cycle in the same direction as DC current injected (positive and negative half-cycle saturation). For comparative necessity, the result without DC bias is also provided.

Multi physical field coupling simulation analysis of power transformer vibration and noise

The generation, propagation and distribution of power transformer vibration and noise are studied by modeling and simulation. Based on the theoretical analysis of the mechanism of power transformer vibration and noise, the correlation between the characteristics of power transformer vibration noise and the influencing factors is determined. The solid model of single-phase power transformer is established by using multi physical field finite element analysis software. The multi physical field coupling simulation of electromagnetic field, structural force field and pressure acoustic field is carried out. The spatial distribution and frequency characteristics of vibration and noise signal of single-phase power transformer in each solution domain are displayed. It provides theoretical and technical support for smart grid equipment detection and environmental noise comprehensive control.

Finite Element CAD Experiments on the Effect of Magnetic Loss in Power Transformers with Laminated Cores

The paper describes a simulated experiment that focuses on the numeric computation of magnetic loss in the laminated core of a single-phase power transformer. The students’ laboratory work is part of the library of experiments of the Electrical Machines virtual laboratory and makes use of the two-dimensional open-access electromagnetic field analysis software Finite Element Method Magnetics. The idea of the simulated exercise is to demonstrate how the magnetic loss caused by time-varying excitations affects the magnetic permeability, μ, of the laminated core and the terminal quantities of the energizing winding. A parametric analysis employing different values for the electrical conductivity and maximum hysteresis-induced angle of the laminated material yields five different field problems with increasing magnetic loss. Electric circuits characterized by the (I-V) operating point and reflected impedance of the energizing winding provide the information required to compute the changes in real power ΔP, reactive power ΔQ and magnetically stored energy ΔWm between successive problems characterized by increasing magnetic loss. The concept of reflected impedance helps to explain the physical meaning of the changes in power dissipation and energy storage in the laminated core.

Experimental simulation analysis for single phase transformer tests

Transformer is one of main components in electrical power system which role to increase or reduce voltage. Characteristics of transformer would be vital to ensure the voltage is fully transferred. A single-phase transformer is a type of power transformer that utilizes single-phase alternating current, meaning the transformer relies on a voltage cycle that operates in a unified time phase. This article describes a workflow executed with Mat lab simulation and practical measurements for single-phase power transformer, no-load, short-circuit test and load test are achieved in this work. The test procedures are implemented on areal transformer (terco-type) which has a specification (1 KVA, 220/110 V, 50 Hz). Finally, the simulation results are appeared a proximately seminar from the practical results. The results indicated that the the technique and manner which presented in the current study can be depended as a miniproject in electrical technology mater for undergraduate studies.

Topologies and Operation Modes of Rail Power Conditioners in AC Traction Grids: Review and Comprehensive Comparison

Electric locomotives in AC traction power systems represent a huge single-phase non-linear load and, detrimentally, affect the power quality and the efficiency of the three-phase power grid. Nevertheless, along the last decades, power electronics are being used to mitigate power quality problems in the three-phase power grid. In particular, Rail Power Conditioner (RPC) helps to increase the loading capacity of traction substations and improve the power quality of three-phase power grids. As the main characteristics, an RPC can supply reactive power, suppress current harmonics and overcome currents imbalance of the three-phase power grid. On the other hand, the traction substations may be constituted by different types of power transformers. For instance, single-phase power transformers and open-delta (V/V) power transformers are widely used, while Scott power transformers are less frequently used, since they are more complex and expensive. In this framework, this work presents a review study of RPC topologies, including their operation modes, and a comprehensive comparison between the characteristics of the RPC topologies when using different types of AC traction substations and power transformers. This helps to ensure the correct selection of the RPC topology for a specific application, according to the main structure of the traction substation. Consequently, and based on the established review, it is possible to sort and allocate each RPC topology for limited or wider applications.

Analytical prediction of initiation of ferroresonance modes

This research focuses on the impact of basic circuit parameters to the initiation of characteristic ferroresonance modes, which is a non-linear phenomenon, in single-phase power transformers. This non-linear phenomenon is investigated using an equivalent circuit of the transformer together with a circuit simulation. The basic circuit parameters investigated were iron core loss, circuit capacitance, and the source voltage. A mathematical method is used to calculate the critical boundary values of each parameter to avoid the occurrence of ferroresonance in the system. In this paper, an analytical method was used to predict the occurrence of ferroresonance while Matlab/Simulink simulation was used to determine the different ferroresonance modes in the power transformers. By varying the circuit parameters, different ferroresonance modes are observed and discussed.

Transformer oil-based magnetic nanofluid with high dielectric losses tested for cooling of a model transformer

An experimental study of dielectric permittivity and dissipation factor of transformer oil-based magnetic nanofluid is reported in this paper. The investigated nanofluid consists of a commercial transformer oil and iron oxide nanoparticles (0.93 % solid volume fraction) coated with oleic acid as a stabilizing agent. Both, the transformer oil and the nanofluid were subjected to measurements of dielectric permittivity and dissipation factor under 1 kV at a power frequency of 50 Hz in the temperature range from 303 to 373 K. The compared results show that the magnetic nanofluid exhibits approximately 4 orders of magnitude greater dielectric losses than the transformer oil. This raised a question about the suitability of such a nanofluid for cooling applications in a transformer. Therefore, the cooling effectiveness of the nanofluid was tested in a model single-phase power transformer under 4.3 kVA load. The prototype transformer was designed with the aim to monitor its temperature at various locations during the load test. It was found that the cooling with the lossy nanofluid does not result in the deterioration of the thermal conditions of the transformer as compared to the cooling with the transformer oil. On the contrary, the tested nanofluid provides a slight decrease in the average transformer temperature rise. Possible reasons accounting for the slight enhancement in the transformer cooling are discussed. The increased thermal conductivity and development of thermomagnetic convection are considered as primary reasons of the cooling effect.

Study of Magnetostriction Influence of Electrical Sheet Steel Under Different DC Biases

Power transformer iron core is mainly composed of electrical sheet steel, which is easily affected by vibration and noise. Therefore, it is necessary to measure the magnetostriction influence of electrical sheet steel. This paper analyzes the performance of vibration and noise in the power transformer iron core considering the magnetostriction influence of electrical steel sheet under different dc biases. First, the butterfly loops of magnetostrictive and magnetic hysteresis loops of electrical steel sheet measured by using a laser displacement magnetostriction measurement system, and the effect of dc bias on magnetostrictive and hysteresis characteristics was analyzed. Second, modeled to single-valued curves along the rolling direction and transversal direction for the finite-element method. Finally, the simulation results of a single-phase power transformer are verified by the experimental results under the dc bias.

Prediction of Outdoor Noise Propagation Induced By Single-Phase Power Transformers

Prediction of Outdoor Noise Propagation Induced By Single-Phase Power Transformers

An optimal and unifying vector fitting method for frequency-domain system identification

This paper proposes an optimal and unifying instrumental variable (IV)-based Vector Fitting (VF) method for frequency-domain (FD) identification of models formed by rational basis function (RBF) expansions. The proposed method is denoted by IV-FD-VF and can be similarly applied for estimating models formed by both continuous- and discrete-time RBF sets. The key advantage of IV-FD-VF lies in the fact that, differently from standard FD-VF approaches, it guarantees an optimal solution after convergence. This important optimality property is proved to be independent of the nature of the noise that corrupts the data (for instance, if it is white or coloured). Two case studies are used to validate the proposed IV-FD-VF method. One of these case studies considers actual frequency-domain data sets extracted from two different single-phase power transformers.

Diagnostics of Winding Deformation in a Single-Phase Power Transformer with an Unloaded Tertiary Winding in Operational Mode

Abstract The presented paper is focused on the development of an algorithm and software implementation of this algorithm into diagnostics of winding deformation in a single-phase power transformer with an unloaded tertiary winding in operational mode. To implement the algorithm, it is necessary to measure instantaneous values of input voltage and current, output voltage and current, and voltage across the unloaded tertiary winding by means of the electric power quality analyzer PQA – 824. This tool is utilized for signal filtering. The inductances of T-shaped equivalent circuit of the transformer were calculated. Relative deviations of the obtained inductance values were determined on the basis of transformer in operation; these deviations were compared with pre-determined set-points. If the inductances deviate from the set-points, the transformer must be repaired. Modern mathematical software package Mathcad 14 is designed to implement the algorithm. As a result of laboratory tests, the error of the proposed algorithm does not exceed 2% in comparison with the exact method.

Analysis of asymmetric magnetization current and reactive power demand of power transformers due to GIC

A comprehensive analysis of the asymmetric magnetization current of single phase power transformers due to geomagnetically induced currents, GICs, is presented in this paper. The aim of this work is to understand the main characteristic of this magnetization current such as peak current and harmonic contents. Usually, computation of the magnetization waveform requires a transient analysis in FEM or EMTP software. Also, the characteristic of the transformer and network parameters are demanded. We introduced a simple and accurate formula for estimation of the main characteristic of the magnetization current. Only general information of the transformer and the network is enough for this estimation. According to the result of this work, also a method for prediction of the reactive power demand is presented.The achievements of this paper are useful for designers of transformers in the calculation of losses due to GICs. Furthermore, the grid owners can have a good prediction of increasing reactive power demands and injected harmonics to the network due to a GIC event.

Analysis and experiment of transformer vibration and noise considering electrical steel sheet magnetostriction

This paper presents the performance analysis and experiment of vibration and noise in transformer cores, considering the different magnetostriction influence of electrical steel sheets in the lamination rolling direction and perpendicular to this direction. Firstly, the magnetostrictive curves are obtained by the experimental test, which are utilized for the accurate setup in the finite element method (FEM). Then, the vibration and noise of a single phase power transformer are analyzed by FEM. Finally, the simulation results are verified by the experimental results under the DC bias.