Showing papers by "Yongjian Li published in 2019"

Eddy Current Loss Effect in Foil Winding of Transformer Based on Magneto-Fluid-Thermal Simulation

Abstract: The foil winding temperature distribution is crucial to the life of power transformer since local heating can accelerate aging of insulation materials. However, based on the traditional 3-D electromagnetic model and the principle of heat transfer, the non-uniform losses and temperature distribution of foil windings are difficult to estimate because of complex magnetic leakage flux. In this paper, the magneto-fluid-thermal coupling model has been established to calculate the temperature rise and predict the potential hotspots of a simplified dry-type power transformer rated at 2500 kVA. Moreover, the influence of insulation barrier is considered to reshape the air-flow path and to affect the radiative effect between the high-voltage and low-voltage windings. Experimental temperature rises are measured with infrared thermography to verify the simulation results, which achieved reasonable hotspot predictions and provide the theoretical method for transformer designers.

Bio-Inspired Magnetostrictive Tactile Sensor for Surface Material Recognition

Abstract: The tactile perception of an object’s surface material plays an important role in many intelligent fields including object recognition, robotic grasp, and environment exploration. Enlightened by the human active tactile perception process that originates from scanning a finger on the surface, a novel finger-like tactile sensor for surface material recognition has been designed according to the transduction mechanism of cilia and Villari effect of the iron–gallium alloy. Based on the structural dynamic theory of Euler–Bernoulli beam, the linear constitutive equations of magetostrictive material and the Faraday law of electromagnetic induction, the output voltage model of the sensor under vibration induced from the fingertip-surface scanning has been established. Furthermore, a prototype of the sensor, on the macroscale, is fabricated. In order to verify the performance, the sensor is used to measure induced vibration signals with texture properties during sliding on the surface and classify five similar texture surfaces with small differences with a classification algorithm. The experimental results indicate that the proposed tactile sensor is effective and highly accurate for surface material classification. The sensor is characterized by high sensitivity and quick response. It has the potential of being miniaturized and integrated into the finger of a robotic hand to realize surface material recognition in real time.

Frequency-Dependent Transport AC Losses of Coated Superconductors Up To Tens of Kilohertz

Abstract: Frequency-dependent transport ac losses of two representative commercial coated superconductors (CCs) at tens of kilohertz band have been experimentally and numerically investigated. It is shown that the ac losses per cycle in metal components of the CCs are not proportional to the applied frequency. Instead, there exists a transition frequency, above which the ac losses decrease continuously. We established a circuit model to understand the underlying mechanism, and found that the current in metal components is not commonly thought eddy current, but a transport current driven by the power supply and surrounding magnetic fields. Meanwhile, we noticed that the geometry of the copper stabilizer plays a significant role on the transport ac losses of CCs, namely, wider copper stabilizers of CCs could bring about much higher losses than theoretical prediction. The underlying reason is the nonuniform current distribution in the copper stabilizers. The obtained results can supplement the existing theoretical description of the ac losses in CCs.

Comprehensive Investigation of Magnetic Properties for Fe–Si Steel Under Alternating and Rotational Magnetizations Up to Kilohertz Range

Abstract: Extensive research and experiments have shown that rotational core loss, which usually exists in the corner joints of multi-phase transformers and behind the teeth of rotational motors, may amount to more than 50% of the total core loss. The frequency of rotational magnetic field can reach even kilohertz level in high-speed motors. In this paper, a new magnetizer of double-yoke vertical structure made of ultrathin steel sheet (0.05 mm) and the corresponding $B$ – $H$ sensing structure are proposed and constructed. Both the alternating and 2-D rotational magnetic properties for non-oriented steel B35A210 and grain-oriented steel B27R090 are measured and characterized up to kilohertz. The magnetic anisotropy of silicon steel is observed and analyzed from its origin mechanism. Moreover, the alternating, 2-D circular and elliptical rotational core losses are compared and discussed. This paper can provide a reference for core loss modeling and the calculation of electrical machines or transformers under different magnetization conditions.

Research of Harmonic Effects on Core Loss in Soft Magnetic Composite Materials

Abstract: A magnetic properties measurement system with the frequency-domain feedback control method is developed in this paper. The system can generate non-sinusoidal waveforms consisting of harmonics with variable orders, contents, and phase angles. Core loss measurement of soft magnetic composite materials under both the sinusoidal and non-sinusoidal excitations is performed. In terms of the harmonic order, content, and phase angle, the effects of harmonic for core loss are analyzed. The frequency-domain Bertotti equations are used to predict the core loss and then compared with the experimental results. The applicability of this method for non-sinusoidal waveforms is also discussed in detail.

Loss Characteristics and Model Verification of Soft Magnetic Composites Under Non-Sinusoidal Excitation

Abstract: A testing platform for the magnetic properties of a ring sample made of soft magnetic composites SOMALOY is established in this paper. The core loss is measured under sinusoidal conditions to verify the original Steinmetz equation (OSE). The accuracy of OSE is improved by modifying the coefficient in the formula. Then it is extended to the modified Steinmetz equation, which is suitable for prediction of core loss under non-sinusoidal excitation. On this basis, the calculated and the measured value under non-sinusoidal excitations with different harmonic orders and contents are compared. The results show that the core loss difference between the calculation and the measurement is very small, which verify the accuracy of the modified model.

Magnetostrictive Tactile Sensor Array for Object Recognition

Abstract: Tactile sensing is used to explore and manipulate objects, which is essential for the interaction with the environment. A novel magnetostrictive tactile sensor array for use in robotic fingers based on smart material, Fe83Ga17 alloy (Galfenol), was proposed. According to the electromagnetism theory, cantilever beam theory, and inverse magnetostrictive effect, the force measurement model of the sensor has been established. The theoretical analysis and experimental verification for the sensor have been carried out. The sensor is sensitive to the force 0–2 N, the maximum value of output voltage is 96.13 mV. We implement the feature extraction and the tactile object recognition on data acquired during an underactuated manipulator equipped with the magnetostrictive tactile sensor array. The actuator positions and tactile sensor values were considered to be available feature data. The proposed approach does not require force modulation and is suitable for gripping arbitrary initial position and orientation of object, so the tactile sensing system can be integrated into the actual robotic gripping and recognizing scenes.

Numerical Calculation and Experimental Verification for Leakage Magnetic Field and Temperature Rise of Transformer Core Tie-Plate

Abstract: According to the actual structure and operation of the transformer, the test model of transformer core tie-plate (TCTP) is designed, and radial magnetic flux density and temperature rise of TCTP surface are measured. In order to reduce solution scale of three-dimensional (3-D) magnetic field, the stray losses in TCTP, tank, and other structural parts are obtained by using 3-D finite element method with surface impedance boundary condition. Then, TCTP temperature rises in different schemes are also calculated by magneto-thermal-fluid weak coupling method. The effectiveness of the used method is validated by comparison of the tested and calculated values of both radial flux density and temperature rise on TCTP surface. It is shown by analysis results that the actual distribution of the temperature rise can be reflected more accurately by the calculation method used in this paper, which provides a more efficient and reliable analysis method to optimize its structure and prevent occurrence of overheating of TCTP.

Measurement and Modelling of the Rotational Core Losses in an Induction Machine at Different Load Conditions

Abstract: To study rotational core losses of induction machines, this paper presents a calculation method based on finite elements method (FEM). This method considers the effect of magnetic saturation and develops transient magnetic flux trajectories to calculate rotational core losses. Moreover, experimental core losses data of induction machine at different load conditions are also presented. The measurement and prediction have shown well agreement, which validates the proposed rotational core losses calculation method.

An Improved Method for Measuring the Magnetic Properties of Silicon Steel With Double Sheets at High Frequency

Abstract: Single sheet tester (SST) is a traditional method for measuring magnetic properties of silicon steel. In order to make the measurement more accurate, this paper presents an improved SST with double yokes and double sheets. The electromagnetic simulation demonstrates that the magnetic field strength H between the two sheets that are in symmetric magnetic path approximately equal to H of two sheets, proving that the improved SST has higher test accuracy than the traditional double-yoked SST. A novel control method is proposed for the measurement system to make sure the symmetry of magnetic path. In this experiment, the magnetic field strength H and the magnetic flux density B of the tested samples are measured by an induction coil method, and the maximum working frequency of this apparatus can be up to 20 kHz.

Vector Magnetic Properties Measurement of Silicon Steel Under Biased Magnetic Excitation Along Laminated Direction

Abstract: Rotational magnetic flux in the plane of steel laminations causes core losses which far exceed than alternating magnetic flux. Traditional testing methods such as Epstein frame detected only in one direction may lead to inaccurate predictions of core losses. This paper developed a 3-D magnetic properties testing device to measure the magnetic properties of high grain-oriented silicon steel. By using the automatic control system and novel surface B-H sensing coils, the dynamic magnetic hysteresis properties of the silicon steel are accurately measured with a static magnetic field along the laminated direction of the specimen. Finally, an ellipsoid magnetic anisotropy model is established which parameters can be identified by the magnetic measurement results with biased magnetic field.

A hybrid Jiles-Atherton/Armstrong magnetization model considering uniaxial anisotropy for magnetostrictive alloy rods

Abstract: A magnetization model for magnetostrictive alloy (Galfenol) rods with uniaxial anisotropy is established, based on the theory of the Jiles-Atherton model and the Armstrong model. The magnetization under different magnetic fields and applied stresses at different directions has been calculated by the constitutive model. The magnetic properties of a Galfenol rod were made and are consistent with the calculated results. The proposed model accurately describes the relationship between the magnetization and applied magnetic field under different stresses for Galfenol rods, in particular, and can be applied to general ferromagnetic materials with uniaxial anisotropy due to crystallography or shape.A magnetization model for magnetostrictive alloy (Galfenol) rods with uniaxial anisotropy is established, based on the theory of the Jiles-Atherton model and the Armstrong model. The magnetization under different magnetic fields and applied stresses at different directions has been calculated by the constitutive model. The magnetic properties of a Galfenol rod were made and are consistent with the calculated results. The proposed model accurately describes the relationship between the magnetization and applied magnetic field under different stresses for Galfenol rods, in particular, and can be applied to general ferromagnetic materials with uniaxial anisotropy due to crystallography or shape.

Modeling of Air Gap Magnetic Characteristics of Anode Saturable Reactors under Impulse Current Excitation

Abstract: In the traditional design process of magnetic apparatus, the core loss is estimated under standard sinusoidal at 50/60 Hz or square waveform excitation at high frequency. However, the air gap of the anode saturable reactor is changing due to vibration and temperature. The air gap limits the magnetic flux density by increasing the reluctance of the magnetic path and avoids core saturation. The quantitative analysis of gapped magnetic core loss and working efficiency have never been reported yet. In this paper, the theoretical calculation and electro-magnetic simulation are carried out to study the effect of shape and length of air gap on core loss and spatial magnetic field distribution so as to improve the loss calculation accuracy of the anode saturable reactor. The loss distribution and temperature rise especially near the air gap region are analyzed to optimize the design.

Electromagnetic Characteristic Calculation of Several Parallel Coils for High Current Transformer Based on Field-Circuit Coupling Method

Abstract: The three-dimensional (3-D) calculation model of FEM coupling with the equivalent electric-circuit (EEC) is established for a test transformer of several parallel coils. Numerical analyses of 3-D magnetic fields, branch currents, additional loss, etc., in coils are carried out by using field-circuit coupling method (FCCM). The validity of the calculated results is verified by comparing with measured value of test transformer. Some distribution rules of electromagnetic characteristics are given for design of high current transformer.

Dynamic Modeling of the Magnetic Properties of Grain-Oriented Electrical Steel under Harmonic Excitation

Abstract: In order to model the magnetic properties of grain-oriented electrical steel under harmonic excitation fast and accurately, a dynamic model combining Tellinen Model with Thin Sheet Model is presented in this paper. The combination of these two models makes the dynamic model require no additional iteration procedure, and have the advantage that the data for establishing the dynamic model are easy to obtain. Only quasi-static major hysteresis loops and dynamic major hysteresis loops under sinusoidal excitation are demanded for model identification. The modeling results are compared with the experimental results tested by Epstein frame. Through error analysis, the dynamic model is further improved by adding a weight function depends on magnetic flux density B. The accuracy of this dynamic model has been demonstrated.

Research of Harmonic Effects on Core Loss in Soft Magnetic Composite Materials Based on Three-Dimensional Magnetic Test System

Abstract: Based on a 3-D magnetic test system with frequency domain feedback control method, core loss measurement of soft magnetic composite materials (SMC) under both sinusoidal and non-sinusoidal excitations is performed. In terms of the harmonic order, content and phase angle, the influence of harmonic for core loss are analyzed based on magnetic domain theory. The Modified Steinmetz Equation (MSE) is used to predict the core loss. The experimental results are convincing by comparing the results from three directions without changing the position of the sample, thence the validity of above theoretical methods is verified.

Considerations of the Magnetic Field Uniformity for 2-D Rotational Core Loss Measurement

Abstract: Rotational core loss data are required for the design and optimization of electrical machine. In this paper, a comprehensive investigation of six typical 2-D rotational magnetizers is given based on 3-D FEM dynamic simulation, considering sample eddy current effect. Particular attention is paid to the magnetic field uniformity of the measured sample, mainly referring to the vibration of magnetic flux density B and distribution of z-component magnetic field intensity Hz in the measurement region. Then, a new 2-D double-yoke vertical magnetizer with ultra-thin steel sheet of 0.05mm, which permits one to conduct the 2-D rotational magnetic measurement up to 2 kHz, is designed, simulated and constructed, The magnetic concentration and shielding are performed to strengthen the magnetization ability and improve the magnetic field uniformity of the sample. The accuracy of this magnetizer is verified by comparing experimental results with the data from standard Epstein frame. Both the alternating and 2D rotational magnetic properties of non-oriented (NO) steel B35A210 are systematically measured and characterized at a broad range of frequency and B.

Comparison between Thermal-Circuit Model and Finite Element Model for Dry-Type Transformer

Abstract: Excessive internal temperature of dry-type transformer with foil windings will accelerate insulation aging and greatly reduce the life-span of transformer. In this paper, a dry-type transformer with low voltage foil windings and high voltage wire windings have been modelled as a simplified equivalent thermal-circuit model, which can improve the computation efficiency. On the basis of this model, the distribution of the internal steady state temperature field obtained by using the finite element simulation is in agreement with the calculation results of the equivalent thermal-circuit model.

Design and Analysis of a Novel Two-Dimensional High Frequency Magnetic Tester for Nanocrystalline Alloy Material

Abstract: To expend the engineering application of novel high frequency magnetic materials, magnetic properties of these materials in different magnetic fields need to be further studied. This paper proposes a novel high frequency two-dimensional (2-D) magnetic properties tester for high frequency magnetic materials, such as nanocrystalline alloy. The magnetic field distribution on the specimen is simulated to verify the theoretical feasibility and rationality of this tester by the finite element software. Considering the dimension and physical properties of specimen, the improved B-H sensing structure is designed that can extract the stable inducted voltage through many experiments and comparisons. Moreover, the frequency-domain feedback control system is used to obtain the desired waveform. Based on the experimental data, measuring error of the tester is systematically analyzed. The losses of square nanocrystalline specimen under alternating magnetization condition are compared with the official data at 20 kHz. The results show that the measurement of the tester has well precision. Finally, the 2-D rotational magnetic properties of nanocrystalline alloy are preliminary measured.