A corrosion diagnosis method for optimized measurement of grounding grids

Simulated experiments of grounding grid corrosion were conducted based on two 220 kV substation models. In initial diagnosis, the measurement nodal points were planned to great span, small piecemeal, and large piecemeal jointing fixed points. A comparative study of the three measurement plans was carried out. The results show that the large piecemeal with fixed points had the best performance and could be used as a practical method for diagnosing grounding grid corrosion.     

Analysis on the effect of substation structure on grounding grid corrosion diagnosis

The measured data of grounding grid corrosion diagnosis are often influenced by steel structural frames, and thus the diagnosis is inaccurate. Based on grounding grid corrosion diagnosis theory, the characteristics of structure frames number, length, layout location and resistance of the influence on the diagnosis result are analyzed by establishing the simulation model. The results show that regardless of the structural frames’ number, layout location and span length, the existence of structural frames reduces the diagnosis sensitivity of fault branch which is near structural frames, making the extent of diagnosed branch corrosion is lower than that without framing. However, the diagnosed corrosion of the branch which is away from the structural frames won’t be influenced. The bigger the resistance of the structural frames connected to grounding grid, the smaller the diagnosis result of interference. Choose the grounding grid branch which has no obvious increase multiples near structural frames as excavation object can improve the diagnostic accuracy.     

Defects detection in the inner surface of pipes based on inverse heat conduction problem

It is a typical ill posed inverse heat conduction problem to estimate the geometry boundary of the inner surface of pipe by the temperature of outer surface. With the establishment of a two dimensional steady model for pipe with irregular inner surface, the inverse problem is transformed into a direct problem and an optimization problem. Based on the temperature at the outer surface obtained from the infrared thermography and the variation of the object function, the conjugate gradient method (CGM) is introduced into the geometry problem. With the numerical analysis of three typical defects, the effects of the measurement errors, choice of the initial value, boundary conditions and number of discrete temperature points are discussed and the proposed methodology is approved.     

The edge element method in the forward problem of magnetic inductiontomography with homogeneous sinusoidal magnetic excitation

The edge finite element method and the imaging visualization have been studied in the forward problem of magnetic induction tomography MIT with homogeneous sinusoidal magnetic excitation. The definite equations of the forward problem were established using the electric field intensity as the vector variable. The edge FE method for solving the definite equations was introduced in detail and realized as the MATLAB program. In order to realize the visualization of MIT in imaging the intracranial hemorrhage, a real human brain finite element model was created with the human head MRI data. On the basis of this model, we realized the 3D visualization of MIT imaging in MATLAB. The research results demonstrated the validity of the definite equations and the edge FE method in calculating the forward problem. And the 3D visualization of MIT imaging with real human brain model established a foundation for the application study of MIT in imaging intracranial hemorrhage.     

An application for detecting faulty insulators based on an inverse problem in local electrical fields

An optimal computing model for detecting poor insulators has been developed based on an inverse problem in local electrical fields. The model takes into consideration the fact that electrical field measurement for insulators requires measuring many points     

Effects of transverse rotating magnetic field on thermocapillary flow under microgravity

Semiconductor melt is electrically conducting, which makes it possible to apply magnetic fields to control the thermocapillary convection induced by surface tension in the floating zone under microgravity, and ultimately to control grown crystal quality. In the present paper, based on the comparison between the transverse static magnetic field and the rotating magnetic field(RMF), we focuses on the effects of RMF on thermocapillary convection. Results indicate that in the RMF, the induced Lorentz force is effective in stirring the melt in the azimuthal direction and suppressing axial convection, and both effects are beneficial for the three-dimensional melt convection returning to a steady axisymmetric flow. The RMF is a promising method for convection control in floating zone for semiconductor crystal growth.     

The Gram-Schmidt orthogonal data fitting method for the designing of the gradient magnetic field of the unilateral NMR

By considering the shortcomings of the traditional Halbach magnet structure which is closed and cannot be applied to the open NMR, an open and semi-circle Halbach magnet structure is proposed. Adjusting the semi-major axis of the elliptic curve which the center of magnets are placed on and calculating the flatness of the magnetic field on different heights, a magnet structure with best flatness is achieved by data fitting method. The optimizing result shows that the best magnet structure can generate a magnetic fields which flatly distributes in the horizontal direction of the 50 mm×50 mm area in the YOZ plane. The gradient is distributed in the vertical direction with gradient of 2 mT/mm. Magnetic field is uniformly distributed in the area of 4 mm×4 mm with uniformity of 1.3×10 -3 and magnetic field of 0.073 9 T. An actual magnet model is constructed based on the result of the optimal design; the measurement result is consistent with the design. The advantage of this magnet structure is that the gradient magnetic field is generated by the permanent magnet naturally, and the extra gradient coil isn’t needed, so the designing of the gradient coding system is simplified.     

励磁功率单元主回路快速故障诊断策略

分析总结了发电机组励磁系统功率单元的故障类型和常见故障,通过Matlab仿真功率单元主回路故障类型,重点研究基于故障频谱分析的定量故障特征提取和故障分类,提出了一种快速针对功率单元主回路的故障诊断真值表法,最后通过实验平台验证故障类别,结果表明：该方法能够正确有效地诊断出功率单元主回路具体的故障晶闸管,为励磁系统功率单元故障诊断提供依据。     

design of an equipment condition monitoring and fault diagnosis network system for the main drive of a hot strip mill

A new distributed equipment condition monitoring and fault diagnosis network system based on an RS485 field bus and an industrial ethernet was designed for the main drive system of a hot strip mill. The system structure and composition were studied. The following problems were resolved: communication of an intelligence data acquisition module with RS485 interface; communication between a server, clients and a light emitting diode; and point to point communication between a programmable logic controller and server. Real time signals of 24 radial run out, 12 axial drifting can be synchronously acquisitioned and stored in a database. System operation is satisfactory and can be used to identify the causes of rolling mill halt and transmission slip brake, and to improve sheet metal quality.     

Magnetic field effect on the fluorescence properties of two metal(II) complexes based on 1,3,5-triazine-2,4,6-triyltrithio-tri-acetate

Two metal (Ⅱ) complexes based on 1,3,5-triazine-2,4,6-triyltrithio-tri-acetate exhibit similar (6,3)-connected 2D layer with kgd topology. Negative and positive magnetic field effects (MFEs) on the fluorescence properties of the Mn(Ⅱ) and Zn(Ⅱ) complexes are observed, respectively.     

Nominal electric field calculation at the ground level of UHV DC transmission lines based on radial basis function method

Nominal electric field at ground level is one of the important factors for the design of transmission lines. FEM meets two big challenges in electromagnetic field computation. One comes from the mesh generation, which is a big difficulty especially in complex geometry. The other is the long time calculation. So the radial basis function method is introduced to calculate the nominal electric field at the ground level of UHVDC transmission lines. Not only the definition and ideas, but also the detailed implementation procedure of radial basis function method are presented. Computer programs are developed to simulate the model and the influences of conductor configuration on nominal electric field intensity are analyzed. Examples of calculation show that the results are accorded with those available literatures, and agreed satisfactorily with analytic solutions of the coaxial cable model. The height of the polar lines and conductor inter-spacing has a remarkable influence on ground nominal electric field intensity while the sub-conductor radius and number of sub-conductors have little influence.