Single Transformer Research Articles

Higher Order Compensation for Inductive-Power-Transfer Converters With Constant-Voltage or Constant-Current Output Combating Transformer Parameter Constraints

Compensation is crucial for improving performance of inductive-power-transfer (IPT) converters. With proper compensation at some specific frequencies, an IPT converter can achieve load-independent constant output voltage or current, near zero reactive power, and soft switching of power switches simultaneously, resulting in simplified control circuitry, reduced component ratings, and improved power conversion efficiency. However, constant output voltage or current depends significantly on parameters of the transformer, which is often space constrained, making the converter design hard to optimize. To free the design from the constraints imposed by the transformer parameters, this paper proposes a family of higher order compensation circuits for IPT converters that achieves any desired constant-voltage or constant-current (CC) output with near zero reactive power and soft switching. Detailed derivation of the compensation method is given for the desired transfer function not constrained by transformer parameters. Prototypes of CC IPT configurations based on a single transformer are constructed to verify the analysis with three different output specifications.

Design of Single Phase Transformer Through Different Optimization Techniques

Selection of an optimization scheme for a particular problem is a complicated issue of whole research community. An Attempt is made for developing an algorithm for finding the optimal design parameters of a low cost small transformer with their own limitations. Most of the engineering optimization problems involve nonlinear objective functions that subject to many constraints. Sometimes it is very difficult to solve such problems by conventional optimization techniques and in some cases it may fail to give the global optima and could be trapped in the local minima. Comparatively the non-classical optimization schemes like Simulated Annealing (SA), Genetic Algorithm (GA), and Particle Swarm Optimization (PSO) etc. are established as a handier tool for Global Search. In this paper an attempt has been made to find an algorithm to obtain the optimal design parameters for designing a minimal cost of material for a 5KVA, 230/115 volt, single phase, core type, and dry transformer using Simulated Annealing (SA) and validating the results with another acceptable method, called Pattern Search (PA). The aim of the paper is to establish an effective and efficient method, which gives more acceptable and improved solution for Global optima, with less no. of iterations and computation time.

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 of Reduction Effect of Three Harmonic Currents by Zigzag Wiring of Single Phase Transformer

Analysis of Reduction Effect of Three Harmonic Currents by Zigzag Wiring of Single Phase Transformer

Study for the electric arc of alternative current at the single phase welding machine using the Matlab/Simulink environment

In this paper is presented a mathematical model of the electric arc for an alternative current welding machine of low power. The electric arc model is based on dividing the voltage-current characteristic of the electric arc in many functioning zones. For the model of the entire welding machine are used real parameters as the ones of the proper welding machine. The voltage and current harmonics spectrum that is obtained during the welding process is presented. Also, the waveforms for the current and voltage of the electric arc plotted against time and the voltage-current characteristic of the electric arc are illustrated. The electric arc is considered as being supplied by alternative voltage from the electrical power network using a single phase transformer which has the output voltage of 80 volts. The model of the welding machine is developed in Simulink and the variations of some parameters of the electric arc are obtained by modifying of them in a Matlab function. Also, in this paper is presented the total harmonic distortion for the voltage and current of the electric arc obtained during simulation of the welding machine.

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.

Performance of Mn-Zn ferrite magnetic fluid in a prototype distribution transformer under varying loading conditions

The temperature distribution performance of prototype transformer has been evaluated for varying loads. A 3 KVA single phase transformer is prototyped for this purpose and thermocouples were inserted at various places for the study. A novel temperature sensitive magnetic fluid (TSMF - Mn-Zn ferrite magnetic fluid) is proposed to improve the cooling performance. Winding temperature reduces when prototype transformer is submerged in TSMF compared to the same experiment performed with transformer oil, for all loading (normal load, under load, overload). The reduction in temperature with TSMF attributes to the thermo-magnetic convection, and it is the maximum when the Curie temperature of the magnetic fluid is comparable to the hot spot temperature of the transformer. The experimental results match with numerical calculation and the existing simulation. The maximum cooling is observed with TSMF for overload condition and increases normal life expectancy nine times. In case of planned overload condition normal life expectancy doubles for all situations. Study leads to the conclusion that TSMF works as a better transformer coolant under all conditions, delivers more power than its nameplate rating without using any external accessories, and improves normal life of transformer. This will reduce the basic investment cost and maintenance of transformer.

Analysis of the Maximum Inrush Current in the Otimal Design of a Single Phase Transformer

The main objective of this work is to design a single-phase distribution transformer core type involved, with the help of optimization techniques to minimize total losses (core and windings). The optimization algorithms used are the differential evolution and particle swarm. His performances and results are compared. Moreover, it is detailed the importance of a good estimate of inrush current in transformers projects, its interference in security systems and electric power system in general. The main parameters of the project, the core dimensions, total losses, the no-load current and the transient magnetization current are computed through Octave software. These values are used to determine the geometry of the active part of the transformer in order to simulate the magnitude of flux density in the transformer core and the losses through finite element method using FEMM (Finite Element Method Magnetics) software. It was through the results the effectiveness of the methodology used, with reducing losses, improving the efficiency and significant decrease of the Inrush current.

A novel single metal layer MEMS-based step-down transformer

This paper presents for the first time single metal layer step-down on-chip transformer. The design is characterized for VHF and UHF frequency ranges. The prototype is coreless (air core), which is suitable for high frequency operations. The design is fabricated in a standard Metal-MUMPs fabrication process, which offers a single structure layer. The primary inductance of 10.7nH and the transformer quality factor of 8.8 have been achieved at 1GHz. The coupling coefficient is 0.60 and the efficiency is 76% with matched load at 1GHz. The total footprint area of micro-transformer is 0.49mm2.

Comparative assessment of different categories of absorption heat transformers in water desalination process

During the last decade, there has been a significant amount of research conducted on absorption heat pumps (AHPs). Second type AHPs, namely absorption heat transformers (AHTs) are useful devices, capable of raising the temperature of waste heat to more useful temperature levels. The excluded heat from AHTs can provide the required energy for desalination. In the present work, performances of three main categories of AHT systems comprising single, double and triple absorption heat transformers (SAHT, DAHT, and TAHT) while they are coupled to water purification system are investigated and compared. A simulation model has been developed in EES (Engineering Equation Solver) to evaluate the effects of several key thermodynamic parameters on the performance of the cycle and amount of desalinated water. The results show that the highest gross temperature lift can be achieved with TAHT while it has the lowest COP among the other types of AHTs. Additionally, a performance optimization performed by using EES shows that SAHT, DAHT, and TAHT can provide fresh water for 853, 796 and 697 residential units respectively if they operate nonstop.

Full-Bridge+SRT Hybrid DC/DC Converter for a 6.6-kW EV On-Board Charger

This paper suggests a hybrid pulsewidth-modulation (PWM) dc/dc converter for an electric vehicle (EV) on-board charger (OBC). It is composed of a full-bridge (FB) converter and a resonant converter with secondary resonance tank (SRT). They are coupled in a single transformer so that any power distribution problem that causes a size increase in the transformer can be solved. Dual power flow of the proposed charger provides an increase in charger gain and a reduction of turn-off voltage spikes of the rectifying diodes caused by transformer leakage inductance and diode junction capacitance. These characteristics help reduce diode loss and remove dissipative snubber circuitry. In addition, this structure has the additional advantage of output inductor size due to the reduction of voltage variation applied to the inductor. The feasibility of the proposed charger is verified with a 6.6-kW prototype implemented by a design procedure.

The response of local power grid at low-latitude to geomagnetic storm: An application of the Hilbert Huang transform

The Hilbert-Huang transform (HHT) is an adaptive data analysis method that can accommodate the variety of data generated by nonlinear and nonstationary processes in nature. In this paper, we focus on the small geomagnetically induced current (GIC) at the local substations in low-latitude power grid of China, responding to a moderate storm on 14–18 July 2012. The HHT is applied to analyze the neutral point currents (NPCs) of transformers measured at different substations, and the GIC indices converted from local geomagnetic field measurements. The original data are decomposed into intrinsic mode functions (IMFs) using the ensemble empirical mode decomposition. After removal of the quasi-diurnal components related with the solar quiet variation, the IMFs representing storm disturbances are transformed into Hilbert energy spectra. The results show that some transformers have more or less responses to the moderate storm in the form of Hilbert energy spectra with the frequency around 2–3 mHz. A comparison on the amplitude changes of the spectra total energy of NPCs' perturbation during storm time intervals at different sites suggests that a shell type of three-phase single transformer group seems to be more vulnerable in the storm. Although the low-latitude power grids usually show very small GIC, these can be used to investigate the potential risk of space weather to the system.

High-Efficient Portable Welding Machine Based on Full-Bridge Converter with ISOP-Connected Single Transformer and Active Snubber

This paper suggests a high-efficiency portable welding machine based on full-bridge converter with input-series-output-parallel (ISOP)-connected single transformer. Link voltage balance problem is theoretically analyzed according to deviations of transformer leakage inductances and transformer turns-ratios and simple voltage-balancing circuit using flying capacitor is introduced to remove this problem. Also, active-snubbing method is also proposed to improve overall efficiency by recovering parasitic resonant energy and regulating the voltage stress of rectifiers to the level that schottky diodes are available. The feasibility of the proposed structure has been verified with 17.5-kW welding machine with 60-kHz switching frequency.

Protected Object Models as the Basis of Distance Measuring Units Algorithms Synthesis

In the present study, the algorithms of distance protection (DP) for a high-voltage transmission line are considered. The single, parallel and tapped transformer lines can be as a protected object. The steady-state and transient modes in the model of protected objects are described by the node-voltage equations, which may be in simplified record either taking into account all parameters or not taking into account some mode parameters. DP efficiency depends on the record form of the node-voltage equations. The programmed distance measuring units algorithms synthesized based on the protected object model are analysed.

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.

TASKS AND METHODS FOR MAXIMIZING THE INSULATION RESOURCE OF POWER TRANSFORMERS

The dependence of transformer service life on the load has been substantiated. Relying thereon, the problem for maximizing the sum of service lives of insulation on transformers in parallel operation and, as a specific case, on a single transformer, has been formulated. It is proved that a maximum will be achieved if the load is completely stabilized over time.

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.

Palm Oil as the Cooling Liquid in Single Phase Transformer for Better Efficiency

The important purpose of mineral oil in transformer is to be insulant and it is role of being a coolant. Petroleum based oil is commonly used because it has a good dielectric strength and cooling performance. However, the application of mineral oil brings negative impact to the environment such as oil spills, leakage, explosion and soon petroleum based oil will be running out for future generation used. Thus, vegetable oil is chosen as an alternative to replace mineral oil for transformer insulation liquid. Formerly, most of Malaysian researches were focusing on the properties of the vegetable oils rather than investigate the effect on the transformer performances after the vegetable oils are applied. Hence, this paper focuses on the performance of the transformer before and after vegetable oils are applied. For this paper, refined palm oil is used as insulation liquid for a single-phase step down transformer which use the 220 V supply and 50 Hz frequency. Transformer is connected to 110V induction motor as load and has been test in two conditions, dry and after palm oil is applied. Comparison is made from both results and clearly shown a good improvement when palm oil is used as insulation oil.

Efficiency Improvement of Single Phase Transformer Using Virgin Coconut Oil

The application of mineral oil in transformer is prominently act as and insulator and a coolant liquid. More often, petroleum based oil is used because most its elements are good to act as insulator such as excellent heat transfer and low in viscosity. Anyhow, the usage of mineral oil in transformer is possibly hazardous to the environment considering that it is poor biodegradable liquid where when a spill or leakage happens, it could pollute the environment surroundings. Moreover, it is known as a non-renewable energy sources, the world will be out of it someday near future. For this reason, a new option of transformer insulation liquid is studied. Vegetable oil is a fully biodegradable insulating liquid and for this paper, coconut oil is used as the insulator. In this paper, it concentrates on the performance of the transformer before and after virgin coconut oil is applied in a single-phase step down transformer that use the 220 V supply and 50 Hz frequency. Transformer is connected to 110V induction motor as load and has been test in two conditions, dry and after virgin coconut oil is applied. Comparison is made from both results and clearly shown a good improvement when virgin coconut oil is used as insulation oil.

Neural Network based Modeling and Simulation for Estimation of Maximum Transformer Inrush Current

Inrush current is a very important phenomenon which occurs in transformer during energization at no load. It depends on several factors like magnetizing properties of magnetic material, resistant and inductance of primary winding, supply frequency, switching angle of circuit breaker, applied voltage etc. Objective of this study is to estimate the maximum value of transformer inrush current. Measurement of inrush current is difficult issue for large rating of transformer under different switching conditions. Therefore this study is used to demonstrate Artificial Neural Network (ANN) for modeling and simulation. This helps in prediction of maximum inrush current for large rating of transformer. Back Propagation with Levenberg–Marquardt (LM) algorithm was used to train the ANN architecture and same was tested for the various data sets. For effective training of ANN various operating conditions are considered. These are Transformer VA rating, Applied Voltage, switching angle and Remnant flux. This study was carried out to develop ANN model in a generalize manner which can be utilize for predicting maximum value of current and harmonic for any single phase transformer provide core material and frequency remains same.