Single-phase Transformer Research Articles

Harmonic PMU and Fuzzy Logic for Online Detection of Short-Circuited Turns in Transformers

Transformers in modern power systems often experience different types of faults due to electrical, mechanical, and thermal stresses during their service life. In this regard, online diagnosis is particularly important to ensure reliable and economic operation of power system by avoiding equipment damages and outages. In this work, a new methodology for online diagnosis of inter-turn faults in transformers is presented. In general, the proposal determines the fault condition through the differential current spectrum and a fuzzy logic (FL) system. For the spectrum estimation, a phasor measurement unit (PMU)-based scheme is expanded to a harmonic PMU (HPMU)-scheme to obtain the magnitude and phase of the harmonic content for the voltage and current signals in a synchronized way. The FL system diagnoses the transformer condition in a continuous and online way. As the proposed method is focused on the online diagnosis of fault, its performance is tested under different operating conditions, including no-load, linear loads, and non-linear loads. To increase the analysis, a simulated three-phase transformer and a real single-phase transformer that present different levels of fault severity for the inter-turn fault condition are analyzed. Results show the effectiveness and usefulness of the proposal.

New Method to Measure Deep-Saturated Magnetizing Inductances for Dual Reversible Models of Single-Phase Two-Winding Transformers

In this letter, a new method is proposed to measure the magnetizing inductances of dual reversible models of single-phase two-winding transformers. Different from all available methods, a dc source is used to excite the transformer to produce deep-saturation through an air-core inductor. A small ac source is applied to the other winding to measure the two magnetizing inductances with only one test, significantly reducing the cost. The cost is further reduced because the necessary equipment is of smaller size than that for the available methods. The proposed method is validated experimentally and with finite elements simulations for two single-phase transformers.

Off-line coupled simulation method for transformer performance assessment under DC bias condition

In this short communication, we intend to introduce an off-line coupled simulation method (OCM) framework for the DC biased power transformer performance assessing. The OCM combined with the electromagnetic transient (EMT) and finite element method (FEM) simulation, which can benefit from fast calculating excitng current and deail representing the transformer’s internal performance. It can be concluded from the numerical results of single-phase and three-phase transformers that it’s feasible to estimate the transformer performance under DC bias condition with the proposed OCM framework, and it’s quite promising in engineering application.

Current modeling in a bus packet of a high-current system

A graphoanalytic method for determining the highcurrent system resistances and a mathematical model of a single-phase furnace transformer with a split secondary winding are developed for modeling currents in a transformer and a high-current system bus package in case of short circuit and opening of flexible connections. Experiments have proved the adequacy of the proposed method. The simulation error does not exceed 10 %. Keywords: single-phase transformer, split winding, short circuit, high-current system, opening, resistance, mathematical model, modeling. timokvey@mail.ru

Universal MHD device for automation of casting control of aluminum

The article proposes an MHD device designed to automate the management of casting aluminum melt from a stationary mixer. The product is made on a modular basis, similar to an induction detachable unit, has three magnetic cores with windings. The design of the MHD device, the location of the magnetic cores, and the features of connecting the windings to the network turn it into a universal unit. The location of the casting trough inside the closed cores allows the device to be used as an MHD pump for aluminum melt. Methods of connecting the windings make it possible to realize the function of dosing the melt using automated process control systems. Pumping the melt through the chute when placing the module between two sockets ensures stirring of the melt in the mixer. The use of a group of single-phase transformers in three-phase switching ensures the movement of aluminum in the channel by creating traction forces in the melt. The presence of windings, allowing for opposition, puts the electromagnetic module into transformer-inductor mode, improving energy efficiency in traction modes, providing melt heating beyond the furnace and maintaining aluminum temperature.

A Class of Single-Phase Z-Source AC–AC Converters With Magnetic Coupling and Safe-Commutation Strategy

This article proposes a family of single-phase transformer based Z-source ac-ac converters (ZSACs). The proposed converters inherit all the benefits associated with the classical single-phase ZSAC, which are providing the buck-boost operation, maintaining or reversing the phase angle, and improving reliability. The proposed converters also have the improved input profile, continuous input current, and shared ground between input and output. Moreover, they use the turns ratio of transformers to produce the required voltage gain, which can be tuned by either increasing or decreasing the turns ratio of transformer depending on the configuration of Z-source structure. A safe-commutation strategy is also presented to achieve the soft commutation, which eliminates the voltage and current spikes without any additional snubber circuits. The features of proposed converters are comprehensively discussed with the detailed theoretical analysis. Thereafter, its performances are evaluated by both simulation and experimental tests.

Fluid Degradation Measurement Based on a Dual Coil Frequency Response Analysis.

Electrical industry uses oils for cooling and insulation of several machines, such as power transformers. In addition, it uses water for cooling some synchronous generators. To avoid malfunctions in these assets, fluid quality should be preserved. To contribute to this aim, a sensor that detects changes in fluid composition is presented. The designed sensor is like a single-phase transformer whose magnetic core is the fluid whose properties will be measured. The response of this device to a frequency sweep is recorded. Through a comparison between any measurement and a reference one corresponding to a healthy state, pollutants presence, such as water in oil or salt in water, can be measured. The performance of the sensor was analyzed through simulation. In addition, a prototype was built and tested measuring water concentration in oil and salt content in water. The correlation between pollutant concentration measured with the sensor and known pollutant concentrations is good.

Modelo del transformador monofásico en el dominio de la frecuencia

This article presents a model in the frequency domain for the analysis of the transient induced overvoltage transfer to the secondary of a single-phase transformer, as well as the distribution of the transient voltage along both windings. The transformer is modeled as an element of distributed parameters from the telegraphist's equations in the frequency domain. The Laplace Numerical Transform (TNL) is used to obtain the solution in the time domain.

New protective relay modeling scheme and analysis for AC electric railway feeding systems with Scott transformer

The Scott transformer is used in substations of the Korean AC electric railway system to convert a three-phase source to a single-phase source. The Scott transformer consists of two single-phase transformers and protects the M-phase and T-phase transformers with a single-phase protective relay. Percentage differential and overcurrent relays are used to provide primary and back-up protection to the Scott transformer. In this study, an overcurrent relay is used, and the protective relay is modeled using the Power System Computer Aided Design/Electromagnetic Transients program including DC (PSCAD/EMTDC). The inverse-time overcurrent relay present in the existing PSCAD/EMTDC will only change the coefficients in a given equation or use limited specifications with the default model. Unlike the existing element, which is limited when configuring the protection operating time, it is possible to obtain the operating time using a specific desired equation and coefficients through the modeled overcurrent relay. This overcurrent relay can be used to model the actual Korean AC electric railway system, and it is verified that the modeling approach that generates a fault in the feeding system is set based on comparison with numerical calculation. Based on this study, we developed a new modeling methodology for the overcurrent relay and for the Korean AC electric railway feeding system. In addition, no national or international standards exist that govern the protection standards for Scott transformers. Therefore, this study is expected to contribute considerably to the design and establishment of protection regulations for Scott transformers.

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.

Investigation of transformers for power electronic converters

A transformer is an integral part of power electronic equipment and it is usually the input stage of a high power converter. A good model of the transformer is needed to evaluate the performance parameters of power converters. This work represent 2 new methods for short-circuit test of single-phase transformers. The paper offers measurement methods that do not require powerful adjustable AC sources. Short circuit parameters can be determined by measuring the parameters of the transient when switching on: i) capacitor under zero initial conditions to an idle transformer or ii) by a transient process when connected to a non-powered short-circuit transformer of a capacitor under non-zero initial conditions. In order to accurately determine the period and the transition process in the event of a short circuit, it is suggested to include a parallel connected battery. PSpice is being used as a simulation tool for analysis and design of power electric circuits.

Electromagnetic and thermal behavior of a single-phase transformer during Ferroresonance considering hysteresis model of core

Ferroresonance leads to a high saturation of the transformer core. This causes severe rise of the amplitude of current and voltage of the transformer and leads to current and voltage non-sinusoidal waveforms. Therefore, the increase of the transformer losses and its temperature rises during Ferroresonance can overstress the transformer insulation system and elevate the chance of the transformer failure. In this paper electromagnetic and thermal behaviors of the transformer during Ferroresonance are investigated using a three dimensional finite element model. The modeling of the core is the most important challenge in the solution of the transformer electromagnetic equations during Ferroresonance. Thus, the Jiles-Atherton (JA) model is employed to model the core hysteresis loop. Based on the proposed approach, the behavior of a single-phase transformer under fundamental and sub-harmonic Ferroresonance modes are simulated and the results are compared with the experimental results. Furthermore, a thermal equivalent circuit is developed, based on the simulated transformer losses and thereby, the transformer temperature rises are estimated during Ferroresonance.

Evolutionary Design Automation of High Efficiency Series Resonant Converter for Photovoltaic Systems

Series resonant converter (SRC) is one of the main parts which has to be designed carefully to be compatible with the general requirements of photovoltaic (PV) grid-connected system. The extensive search space for design parameters of SRC such as resonant tank component values, transformer turn ratio, dead time and switching frequency requires an automated design framework. The proposed framework is developed using genetic algorithm (GA), differential evolution algorithm (DEA), and nondominated sorting genetic algorithm (NSGA-II) for the multi-objective optimization of SRC circuit while accomplishing zero voltage switching (ZVS). Regulating the output voltage while minimizing the losses of MOSFET, diode and transformer are the design objectives. FEM is applied to subdivide the single phase transformer into simpler and finite parts to calculate flux density value according to the optimized design parameters. Amongst these evolutionary algorithms, NSGA-II achieved the best optimization performance considering various operation modes and required specifications. Simulation results are also provided to validate the efficient and robust automated design of SRC to be used in photovoltaic systems.

Analisa Stray Losses Pada Struktur Transformator Daya Satu Fasa 275 Kv 83.3 MVA

Background The jurnal discusse stray losses are generated by eddy current losses in the single phase transformer construction parts, such as Main tank, cover,core clamp and flitch plate. Stray losses can’t measurement direct and only calculated. 
 Aim This study is to accurate calculated stray losses are generated in the single phase transformer construction parts in order to get more accurate calculated compared with measured and to know calculation versus measurement and versus simulation.
 Method This study using 3D Finite Element Metode with basis software ANSYS in the single phase transformer construction parts 
 Result The stray losses in the single phase transformer construction parts, so that it hasn’t a simple stray losses divided by 3 compared to three phase transformers with same power and voltage. 
 Conclusion Base on this study the total stray losses around 30%-37% from Load Losses and impove approxi-mately 9% compared between existing calculation and this simulation study versus measurement. 

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.

Modeling of the Dispersion Magnetic Fields for the Single-Phase Transformers

Abstract Different methods of dispersion magnetic fields solutions for single phase transformers are presented in this paper. The transformers are with cylinder windings placed onto a single column. The transformer construction transformer is in the mantle. The analytic equation expression of finding dispersion magnetic fields have been delivered and the obtained solution has been verified by the experimental field measurements.

Importance of core joints in GIC/dc studies with scaled down laboratory transformers

The response of large power transformers to geomagnetically induced currents (GICs) cannot be tested fully in factories because of the significant reactive power required. While carrying out physical tests on scaled-down models of a power transformer, we discovered that models with high-grade electrical core steel and even a transformer tank, as widely used in investigating the bias effects of GICs and leakage dc, cannot replicate adequately the actual performance if they are built without relevant construction details. Laboratory testing and FEM simulation of three single-phase four-limb transformers show that transformer models need multi-step lap mitered joints similar to those in full-scale power transformers to reproduce correctly the saturation response to dc components. FEM simulation also shows the change of transformer inductance when driven into deep saturation, as required in equivalent circuit models. The approach of achieving consistency between equivalent circuit, FEM and physical models even in the presence of saturable core joints is a novel contribution which provides guidance for future research in slow transient phenomenon studies.

Electromagnetic analysis of single-phase transformer banks under sympathetic inrush phenomenon

Electromagnetic analysis of single-phase transformer banks under sympathetic inrush phenomenon

Residual Flux Measurement of the Single-Phase Transformer Based on Transient Current Method

When the no-load transformer is connected to the power grid, an inrush current may be resulted as the existed residual flux in the transformer core. To suppress this inrush current, the detail information of the residual flux needs to be known. In this paper, a transient current method for obtaining the residual flux density in the single-phase transformer is proposed. Firstly, two DC voltages with opposite polarities are sequentially applied in the measuring winding, and then two corresponding transient response currents can be detected. Based on above information, an empirical equation in regarding of the residual flux density and the transient current difference will be obtained. To make sure the initial residual flux density does not change greatly, the magnitude of the DC voltage has been determined as well. Finally, the proposed method is verified by the experiment results.

Power quality enhancement of a T-connected autotransformer based on 72-pulse AC–DC converter with rated power reduction

In this paper, a thorough analysis is carried out in order to achieve an optimal design of a T-connected autotransformer based on 72-pulse AC–DC converter. Accordingly, the main purpose of the paper is focused on the power KVA rating reduction for power quality applications. The first merit is that the T-connected autotransformer configuration requires two single-phase transformers, which is more economical (in weight and volume) as compared with other topologies using three single-phase transformers. The second one is that the application of the pulse doubling technique with a low power rating (0.6% of the load power rating) results in a simpler and more economical configuration of the whole system and increased number of pulses. It provides a more economical solution to achieve harmonic mitigation in electric power systems as compared with other 72-pulse AC–DC converters. The simulation and experimental results show that the input current THD is less than 3% using the proposed topology. The results indicate a significant reduction in the total cost and volume of the proposed 72-pulse configuration in comparison with similar configurations. Also, it is shown that the proposed converter rating is about 43.61% of the DC load power.