Single-phase Power Transformer Research Articles

FEMAG: A High Performance Parallel Finite Element Toolbox for Electromagnetic Computations

This paper presents a parallel finite element toolbox for computing large electromagnetic devices on unstructured tetrahedral meshes, FEMAG—Fem for ElectroMagnetics on Adaptive Grids. The finite element toolbox deals with unstructured tetrahedral meshes and can solve electromagnetic eddy current problems in both frequency domain and time domain. It adopts high-order edge element methods and refines the mesh adaptively based on reliable and efficient finite element a posteriori error estimates. We demonstrate the competitive performance of FEMAG by extensive numerical experiments, including TEAM (Testing Electromagnetic Analysis Methods) Problem 21 and the simulation for a single-phase power transformer.

식물성 절연유 변압기의 냉각특성 변화에 따른 최고점온도 특성 해석

Natural ester has a higher biodegradability, flash and fire points, and a greater permittivity compared to conventional mineral oils. However, natural ester also has a higher pour point, viscosity, and water content. These characteristics hamper circulation and the electrical properties of oil-filled transformer. Thus, this paper applied electromagnetic-thermal-flow coupled analysis method to predict temperature distribution inside 154kV single phase power transformer using natural ester. It modeled in the actual appearance for the tank and winding of the power transformer to improve the accuracy of analysis and applied heat flow analysis that considered hydromechanics and heat transfer at the same time. It calculated the power loss, the main cause of temperature rise, from winding and core with electromagnetic analysis then used for the heat source for the heat flow analysis. It then compared the reasonability of result of measurement analysis based on the result acquired from temperature rise test using FBG sensor on the power transformer.

Cost Optimal Design of a Single-Phase Dry Power Transformer

The Dry type transformers are preferred to their oil-immersed counterparts for various reasons, particularly because their operation is hazardless. The application of dry transformers was limited to small ratings in the earlier days. But now these are being used for considerably higher ratings. Therefore, their cost-optimal design has gained importance. This paper deals with the design procedure for achieving cost optimal design of a dry type single-phase power transformer of small rating, subject to usual design constraints on efficiency and voltage regulation. The selling cost for the transformer has been taken as the objective function. Only two key variables have been chosen, the turns/volt and the height: width ratio of window, which affects the cost function to high degrees. Other variables have been chosen on the basis of designers’ experience. Copper has been used as conductor material and CRGOS as core material to achieve higher efficiency, lower running cost and compact design. The electrical and magnetic loadings have been kept at their maximum values without violating the design constraints. The optimal solution has been obtained by the method of exhaustive search using nested loops.

Reduction of Vibration and Sound-Level for a Single-Phase Power Transformer With Large Capacity

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.

Harmonics Performances of Single Phase Transformer due to DC Bias

The investigation of the direct current (dc) bias effect on single phase power transformer through their harmonics performance is present in this paper. The experimental study is done by the dc bias current injected simultaneously with alternating current (ac) source to primary winding of transformer. The input ac voltage to primary winding is maintained constant during investigation and the dc currents increased gradually. Compare to pure ac power applied, the results show that the waveforms distorted when the dc bias exist. The pulsated waveforms are pushed to half cycle in which the bias current is in the same direction as magnetizing current (unsymmetrical pulsated) and even harmonics are significant.

Диагностика однофазного силового трансформатора в рабочем режиме

The use of L-shaped equivalent circuit of the transformer is proposed for the diagnosis of a single phase power transformer. It's required to measure the instantaneous values of the primary voltage, the secondary voltage and secondary current by means of electric power quality analyzer PQA - 824, to measure the temperature of the transformer windings. For active power losses in the windings and the current value of the reduced secondary current to calculate the resistance of the windings. Using the differential equation RL-circuit with constant parameters to calculate the average value of the inductance of the windings on the period. To reduce the error in the determination of changes in the active and inductive reactance of the windings, filtering of the measured signals based on the Fourier transform has been used, as well as the adjustment of the winding resistance according to temperature. Then it's required to determine the relative deviation of the obtained values of resistance and inductance of the windings of the variables defined on a proper transformer, while comparing the obtained deviation to the settings. If deviations obtained more of the defined settings, then it is the failure occurrence of the diagnosed transformer of the windings. A modern mathematical software package MathCad 14 is designed to implement this algorithm. Audited algorithm using this analyzer is tested in the laboratory. The results of the test are verified.

변압기 절연유의 물성치 변화에 따른 온도특성해석

In this paper, the temperature distribution according to the property change of the insulating oil of the power transformer and max temperature were predicted through the ductility interpretation which heat-flow is coupled. By using CFD (Computation Fluid Dynamics) for the interpretation, the temperature distribution of 154kV the class single phase power transformer was predicted. The power loss causing the temperature rise of the transformer was changed to the heat source and we used as the input value for the heat-flow analysis. The temperature distribution was predicted according to the change of the density, specific heat, thermal conductivity and viscosity, that is the ingredient having an effect on the temperature rise of the transformer oil. The mineral oil of 4 kinds used in domestic and international based on the interpreted result was selected and the temperature distribution according to each load and Hot Spot temperature was predicted.

An experimental study of winding vibration of a single-phase power transformer using a laser Doppler vibrometer

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.

Virtual Laboratory for Performing Tests on a Single-Phase Power Transformer

ABSTRACTThis paper presents a virtual laboratory for testing a single-phase power transformer using MATLAB Simulink environment. The models presented herein replicate the actual tests like no-load test, short-circuit test, load test, and short heat run test successfully well within tolerable accuracy. The rating of the transformer is taken to be 2 kVA, 230/115 V, 50 Hz which is a typical rating for transformers usually employed for practical classes in the Electrical Machine Laboratory for undergraduate courses. This model is attractive to students and they are able to gain insights into operational aspects of a single-phase power transformer. This model, in whole or part, may also be used as final year projects of engineering undergraduate students.

Synchronous generator for induced AC voltage test of single-phase and three-phase power transformers

Synchronous generator for induced AC voltage test of single-phase and three-phase power transformers

Bidirectional impedance-type transformer inrush current limiter

Transformer inrush current is harmful to the transformer's windings and may bring about inadvertent tripping of the protective relays. In order to reduce the magnitude of inrush current, a bidirectional impedance-type inrush current limiter (BIT-ICL) is proposed in this paper. When a power transformer is energized, the BIT-ICL immediately and automatically inserts into the circuit to suppress the inrush current without any control or detection circuit. After completing transformer inrush suppression, the BIT-ICL is bypassed automatically, and the transformer appears to connect directly to the voltage source. Thus, when the transformer is loaded, there is almost no distortion in the steady-state load voltage and current waveforms due to the voltage-compensation effect in the limiter. The feasibility and performance of the proposed BIT-ICL are verified by a low-voltage single-phase power transformer under different residual flux and load conditions. Moreover, as long as the power loss that results from the related components in the BIT-ICL can be greatly reduced, this limiter can be applied to high-voltage and large-capacity distribution transformers.

Modelling of inrush current in transformers using inverse Jiles–Atherton hysteresis model with a Neuro-shuffled frog-leaping algorithm approach

This study presents a novel approach for modelling inrush current transient in power transformers taking into account the hysteresis effect. Inverse Jiles-Atherton (JA) model is used to represent the hysteresis phenomenon in the magnetic core. The parameters of this model are optimally determined using inrush current measurements by shuffled frog-leaping algorithm (SFLA). Then, an adaptive technique to enhance the accuracy of the proposed model for simulation of inrush current in other possible conditions is proposed. The method is based on artificial neural network which is used for updating the inverse JA hysteresis model parameters in each hysteresis loop during a power frequency cycle. SFLA optimisation is used for accurate parameter determination from measured inrush currents in training stage. The measurements are performed on a single-phase power transformer and the results verify the performance of the proposed neuro-SFLA approach.

Computation of 3-D Magnetic Leakage Field and Stray Losses in Large Power Transformer

A time-stepping finite element method combining analytical and numerical solutions for laminated-material homogenization is proposed to calculate 3-D magnetic leakage field and its structural parts stray losses in a 380 000 kVA/500 kV single-phase power transformer, and the high-order harmonics of field components can be considered. To verify the method and computation code, a supplementary model of Team Problem P21C-M1 is made. Measured and computed results to the model indicate the validity of the method proposed.

Voltage compensation-type inrush current limiter for reducing power transformer inrush current

When a transformer is initially energised, its iron core is driven into saturation, which will result in high-amplitude magnetising inrush current. For lessening this transient phenomenon, a voltage compensation-type inrush current limiter (VCT-ICL) is presented in this study. The VCT-ICL can automatically insert high impedance to restrain the sudden change in line current. After completing the restriction of inrush current, the VCT-ICL freewheels, and acts as a short circuit. Thus, other than performing the restriction, the VCT-ICL has a negligible effect in the circuit and the transformer seems to connect directly with the voltage source. When a load is connected at the secondary side of the transformer, to adjust the magnitude of DC reactor current so that it is equal to or higher than the peak of line current, there is almost no distortion to the load voltage and current waveforms during the steady state. A 5 kVA single-phase power transformer is used as an example to demonstrate the performance of the proposed limiter. According to the simulated and experimental results, the feasibility of the VCT-ICL has been verified. Moreover, increasing the insulation levels of the related components in the proposed limiter allows it to be applied in high-voltage distribution transformers.

Investigation of GIC effects on core losses in single phase power transformers

Investigation of GIC effects on core losses in single phase power transformers This paper presents a method for estimation of core losses in banks of single phase power transformers that are subjected to an injected DC current such as geomagnetically induced currents (GIC). The main procedure of the core loss calculation is to obtain a magnetic flux density waveform in both time and location by using a novel algorithm based on 3D FEM inside the core and then to calculate the loss distribution based on loss separation theory. Also, a simple and effective method is proposed for estimation of losses of asymmetric minor loops by using combination of symmetric loops. The effect of DC biasing on core losses in single phase power transformers is investigated and the sensitivity of core type and material is evaluated. the results shows that DC current biasing could increase core losses up to 40 percent or even more.

Prediction of magnetising current waveform in a single-phase power transformer under DC bias

Direct current (DC) flowing through the earthed neutrals of transformer windings causes a DC component in the magnetising current. Owing to non-linearity, the waveform of this current is strongly distorted. A method based on the finite element analysis of a transformer is presented that is capable of predicting the waveform of the magnetising current with the voltage of the winding as well as the magnitude of the DC bias given. The relationship between the flux linkage of the winding and the value of the magnetising current is determined, with static conditions assumed. With the aid of this flux–current curve, the dependence of the waveform and thus of the DC component of the magnetising current upon the bias flux is established. Hence, the flux bias yielding the given DC component is obtained by suitable iterative techniques, arriving at the waveform of the magnetising current with the prescribed DC value. Measurement of the current waveform at various voltages and DC bias has been carried out on a single phase transformer. The computed waveforms agree well with the measured ones.

Computation of inrush current forces on transformer windings

Inrush currents are frequently encountered during the switching process of transformers. The purpose of this paper is to present an investigation of forces that appear as a result of inrush currents. While both short circuit and inrush transformer situations might seem identical, they vary significantly from the core magnetization viewpoint. Three-dimensional computations have been carried out on a typical single-phase power transformer using the Hopfield neural network energy minimization technique. Results are given in the paper as well as comparison with short circuit forces.

Test of a high T/sub c/ superconducting power transformer

A single-phase power transformer with windings made of T/sub c/ superconducting tapes was fabricated and tested. The tapes are made of Bi-2223 imbedded in a silver alloy matrix. The primary and secondary windings are made of double pancake coil. The rated voltages of the windings are 220/110 V. Four pancake type coil windings are stacked on the core. The inner two act as the primary winding. Fundamental characteristics are obtained through short circuit and no load tests. The overload capability and characteristics are investigated.

Single phase 1-kVA amorphous core transformer: design, experimental tests, and performance after annealing

The design and experimental implementation of a single-phase power transformer operating at 1 kVA, 110/220 V, and 60 Hz, with an amorphous alloy core are described. The prototype core material is annealed in an argon atmosphere, under a DC magnetic field applied along the ribbon length. The experimental results are presented to compare the amorphous core transformer performance with another transformer with the same rated power, but with a silicon steel core.

FEM analysis of DC saturation to assess transformer susceptibility to geomagnetically induced currents

Results are presented of a systematic finite element (FEM) simulation of power transformer susceptibility to geomagnetically induced currents (GICs). DC saturation patterns for five different transformer core designs are examined using FEM. Magnetic fields along various traverses are provided. Impedance matrix entries of a single-phase power transformer are compared for normal and DC saturation operations. The fundamental transformer magnetization mechanism under GICs is discussed. >