International Journal of Applied Electromagnetics and Mechanics - Volume 60, issue 1

Authors: Zhang, Bo | Lu, Ping | Kong, Jinjiao | Liu, Rui | Cao, Quanliang | Shao, Hongbo | Deng, Wanting | Chen, Jun

Article Type: Research Article

Abstract: An actual occurred ground-fault accident of 500 kV transformers in HVDC converter station is presented. A 2D transient electromagnetic-thermal-mechanical finite-element coupling model of 500 kV transformer is developed to analyze the transient process of failure, with consideration of the resistance-temperature relationship and plasticity displacement in the windings’ thermal and mechanical characters. To verify the proposed finite-element model, the model is calibrated by pre-fault field test of the transformer in steady state, which shows good agreement with measurement. The short-circuit current adopted in simulation is based on actual on-site measurement of the ground-fault accident. By using the proposed model, simulation results …reflect the transient process and explain the post-fault inspected damage well in term of over burn regions in thermal analysis and deformation tendency in mechanical analysis when compared with field post-fault inspection photos. Show more

Keywords: Electromagnetic analysis, finite-element, transformer, ground-fault accident and DC grid

DOI: 10.3233/JAE-180082

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 60, no. 1, pp. 1-12, 2019

Authors: Wang, Siqi | Liu, Yongkai | Li, Decai | He, Xinzhi

Article Type: Research Article

Abstract: This paper proposes a ferrofluid-based tuned mass damper with magnetic spring that is capable of absorbing the low-frequency vibration energy. The characterization and performance of the tuned mass damper are studied in theory and experiment. Ferrofluid is adhered on the moving permanent magnet and used as self-sustained viscous lubricant to reduce the mechanical damping between the permanent magnet and the inner wall of plastic tube and improve the ability of the vibration pick-up system. A magnetic spring is formed by magnetic repulsive force between the fixed and the moving permanent magnets along the horizontal axis. The tuned mass damper can …effectively reduce the low frequency vibration of the rod. And the damping time in the cases of released permanent magnet is 1/6 times as long as that in the cases of blocked permanent magnet. The compact tuned mass damper with adjustable damping and stiffness is suitable to various low frequency vibrations in nature. Show more

Keywords: Ferrofluid, magnetic spring, damper, vibration

DOI: 10.3233/JAE-180056

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 60, no. 1, pp. 13-19, 2019

Authors: He, Xinzhi | Wang, Li | Yu, Jun | Li, Decai

Article Type: Research Article

Abstract: Magnetic fluid seal is the most important and mature application of magnetic fluid. Usually, gravity is ignored when analysing the performance of magnetic fluid seal and designing magnetic fluid sealing devices. With the expansion of magnetic fluid seal applications, gravity could seriously affect the performance of magnetic fluid seal, especially when the “O” ring diameter of magnetic fluid and sealing gap are both large. In this paper, the influence of gravity on the anti-pressure ability of magnetic fluid seal is theoretically analysed and proven by the experiments. The results show that magnetic fluid seal has a limit size that is …directly proportional to the magnetic field gradient in the sealing gap and is inversely proportional to the ratio of magnetic fluid density to the magnetization. If the diameter of the magnetic fluid “O” rings, whose centre axis is perpendicular to the direction of gravity, is far smaller than the limit size, the influence of gravity on the anti-pressure ability of magnetic fluid seal can be neglected. However, if the size is close to or greater than the limit size, gravity would lead to a drop in the anti-pressure ability of magnetic fluid seal. Show more

Keywords: Seal, magnetic fluid, gravity, sealing limit size, anti-pressure

DOI: 10.3233/JAE-180054

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 60, no. 1, pp. 21-32, 2019

Authors: Zhai, Luxin | Han, Bangcheng | Liu, Xu | Zhao, Jianhui

Article Type: Research Article

Abstract: Magnetic-bearing reaction wheel (MBRW) can be applied to stabilizing satellites with stringent pointing accuracy. Temperature rise subjected to losses is a key issue for a MBRW. The prediction models of iron loss and copper loss for magnetic bearings and BLDCM are established, and the loss coefficients of iron core are determined by measured loss curves at different frequencies. The copper loss distribution and iron loss distribution of the MBRW are investigated. Based on the loss values, the heat generation rates of the different parts in the MBRW are calculated, then the thermal field of the prototype is analyzed by 3-D …finite element model. Thermal-structure coupled analysis of rotor is also investigated. Finally, the prediction and analysis of losses are verified by experimental results in a prototype of MBRW with rated speed of 5000 r/min and rated angular momentum of 15 Nms. Show more

Keywords: Magnetic bearing flywheel, iron loss, magnetic bearing, BLDCM, finite element model

DOI: 10.3233/JAE-180049

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 60, no. 1, pp. 33-53, 2019

Authors: Mehboob, Nasir | Nasir, Muhammad Farooq | Grössinger, Roland | Oser, Peter | Kriegisch, Martin | Fulmek, Paul

Article Type: Research Article

Abstract: Frequency and temperature dependence of the hysteresis loops (both major and minor hysteresis loops) of well-known materials such as pure Fe and pure Ni in the as-cast state and after a heat treatment, were measured and analyzed. Furthermore temperature dependent magnetostriction of the as-cast and annealed Ni sample were measured and residual stresses were estimated by assuming the magnetoelastic energy as the origin of coercivity H c . The hysteresis measurements were made on fully automized hysteresigraph which is handled by a labview program. The system works with ring- or frame-shaped samples in the frequency range from 0.1 Hz to …2 kHz and in the temperature range from −77 K to 493 K. Show more

Keywords: Magnetic hysteresis, coercivity, residual stresses, magnetostriction

DOI: 10.3233/JAE-170075

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 60, no. 1, pp. 55-62, 2019

Authors: Bu, Wenshao | Li, Biao | He, Fangzhou | Li, Jinwei

Article Type: Research Article

Abstract: Bearingless induction motor (BLIM), is a nonlinear, multivariable and strongly coupled object. In order to improve its dynamic decoupling control performance, and overcome the influences of the load disturbance and the motor parameter variation, under the conditions of considering the stator current dynamics of the torque system, the inverse system model of BLIM system is established firstly, and by the inverse system method, the BLIM system is decoupled into four second-order pseudo linear subsystems. And then, according to the sliding mode control (SMC) theory, the SMC regulator is designed for each subsystem, an exponential approach law is used to reduce …the chattering of SMC system; the stability of SMC system is verified by the Lyapunov method. Simulation experimental results have shown that the inverse system decoupling SMC system not only has an excellent dynamic decoupling control performance, but also has a faster response speed and a stronger robustness. Show more

Keywords: Bearingless induction motor, current dynamics, inverse system decoupling, sliding mode control, anti disturbance ability

DOI: 10.3233/JAE-180094

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 60, no. 1, pp. 63-78, 2019

Authors: Li, Xiangchao | Wan, Zhicheng | Liu, Yinping | Ma, Xiaoqi | Cai, Lujin | Xu, Xiaopei

Article Type: Research Article

Abstract: In order to study the problem of damage that caused by lightning overvoltage to the transistor, we designed the experiments of combined wave impact on the transistor under different conditions by analyzing the theory of the secondary breakdown of the transistor caused by the lightning electromagnetic pulse. These cases are carried out under the condition of no protection, transient protection diode (TVS) parallel protection, and TVS tube parallel protection in the actual base amplifier circuit. It is concluded that transistor can cause it to further deteriorate under the condition of lightning overvoltage impact, and the situation of the damage can …be divided into two categories, transient suppression diode in parallel with a transistor that is struck by a lightning voltage can effectively protect the transistor, which can obviously improve the resistance of the transistor. In practical amplifying circuit, applied voltage reduces the tolerance level of transistors, however, the tolerance level of transistors with transient suppression diodes in parallel is still better than the tolerance level without protection, which confirmed the conjecture that transient suppression diodes can be applied to actual circuits to protect transistors in parallel. In this paper, the theoretical analysis and experimental research on the damage of the lightning voltage on the transistor, the tolerance level of the transistor to the lightning voltage and the protection effect of the TVS tube on the transistor are carried out, which has certain reference value in the actual lightning protection of the transistor. Show more

Keywords: Crystal triode, lightning overvoltage, secondary breakdown, transient suppression diode

DOI: 10.3233/JAE-180092

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 60, no. 1, pp. 79-89, 2019

Authors: Li, Xiangchao | Cai, Lujin | Xu, Xiaopei | Wan, Zhicheng | Ma, Xiaoqi | Liu, Yinping

Article Type: Research Article

Abstract: Corona plays an important role in both initiation and development process of leaders around wind turbine blades. In this paper, based on laboratory experiments and numerical simulation, the corona triggering tests are performed by analyzing corona discharge characteristics of wind turbine blades. The corona threshold voltage and the corona current are measured. The corona environmental threshold and the corona triggering threshold are evaluated and discussed in detail. The influence of blade lengths, rotational angles and rotational speeds is analyzed. The results show that the corona trigger threshold obtained is a constant and is about 321.29 kV/m, which appears to be some fluctuations due …to atmospheric conditions and charged ions. In addition, through analysis the corona triggering threshold of different rotational angles and the corona environmental threshold of different rotational speeds, rotational wind turbine blades affect the electric field near the blades by varying the blade height and the charged ions distribution at the tip of the blades where the altered blade height accounts for the dominant factor. The above research results are valuable for the understanding of the initiation and development of leaders around the wind turbine blades. Show more

Keywords: Wind turbine blades, electric field distortion, corona discharge, corona triggering threshold, corona environmental threshold

DOI: 10.3233/JAE-180085

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 60, no. 1, pp. 91-101, 2019

Authors: Park, Eui-Jong | Gim, Chan-Seung | Jung, Sang-Yong | Kim, Yong-Jae

Article Type: Research Article

Abstract: A magnetic gear, which can transfer torque without contact, has many advantages over mechanical gears. These advantages include high-efficiency and high-reliability. Consequently, the magnetic gear is utilized in many different fields of study. However, because the magnetic gear uses NdFeB permanent magnets (PMs) for high power density, eddy-current loss can occur. Eddy-current loss is very problematic because it is the main factor that reduces torque transfer efficiency. Therefore, in the present study, we calculated the eddy-current loss from PMs at different rotational velocities by using a nonlinear finite element method (FEM) based on a three-dimensional numerical analysis, and analyzed how …the eddy-current loss affects the torque transfer efficiency. Furthermore, we proposed a new geometry for the magnetic gear to reduce the eddy-current loss of PMs and improve the torque transfer efficiency. Show more

Keywords: Magnetic gear, permanent magnet (PM), eddy-current loss, torque transfer efficiency, finite element method (FEM)

DOI: 10.3233/JAE-180055

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 60, no. 1, pp. 103-112, 2019

Authors: van der Horst, Menno Patrick | van Kreveld, Sylvia Lyanne | Kaminski, Miroslaw Lech

Article Type: Research Article

Abstract: Wireless crack monitoring on ships and offshore structures based on Self Magnetic Flux Leakage (SMFL) measurements is a promising method to guarantee the structural integrity in a more effective way, leading to reduced operational costs and increased safety. For accurate crack sizing, the SMFL measurements must be interpreted correctly, also during cyclic loading. Not much research has been done that focus on the effect of high cyclic stresses on the magnetization of ferromagnetic steels in weak magnetic fields. The aim of the research presented in this paper is to investigate the effect of stress-induced magnetization on the SMFL in the …stress concentration zone of a structural steel plate, and its implications for crack monitoring by the SMFL method. By means of an experiment, measured stress magnetization curves were obtained in a grid of points around an elliptical hole in a steel plate that was cyclically loaded up to the yield stress. The results show that the stress-induced magnetization causes a maximum variation of the measured signal of 25 μT, which is fully reversible. It is concluded that, depending on the application, this stress-induced variation may need to be taken into account for the interpretation of the measured signals by a crack monitoring system using the SMFL method. Show more

Keywords: Crack monitoring, self magnetic flux leakage, stress magnetization, ferromagnetic steel, cyclic loading

DOI: 10.3233/JAE-180031

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 60, no. 1, pp. 113-130, 2019