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The sensors of logging-while-drilling (LWD) azimuth propagation resistivity (APR) tool are usually installed in the annular antenna recesses filled with ferrite or other magnetic materials on the grooved metal mandrel. In this article, we will improve the 3-D finite volume method (3-D FVM) on cylindrical grids to solve the Helmholtz equations about coupled potentials for precise simulation of the tool responses with multiple antenna recesses. The irregular and novel Yee’s staggered grids are designed to conform to the grooved mandrel surface. The electrical continuation technique is adopted to approximate the perfectly electrical conductor (PEC) boundary condition on the mandrel surface for efficient enhancement of the discretization precision of the potentials around the mandrel. The equivalent conductivity and permeability in heterogeneous elements are determined by the volume average. After that, the parallel direct sparse solver (PARDISO) is used to solve the discretized equation about coupled potentials for effectively ensuring the accuracy and stability of numerical solutions. Finally, we validate the 3-D FVM against results by the hybrid algorithm in homogeneous formation. Through numerical results, we further investigate the influence of both the mandrel and antenna recesses on the LWD tool responses, and its response characteristics in several different environments. [ABSTRACT FROM AUTHOR]

This paper introduces a voltage-controlled static magnetic device called magnetic flux valve. It is mainly used in a magnetic circuit to actively control the magnetic flux through the magnetic circuit. The magnetic flux valve has a laminated structure of two different types of layers made of a magnetostrictive material, e.g., amorphous alloy ribbon, and a piezoelectric material, e.g., piezoelectric sheet. The permeability of the magnetostrictive layers changes when an external control voltage applied to the piezoelectric layers changes, which is known as the converse magnetoelectric effect. A permeability change of the magnetic flux valve will lead to a change of the reluctance of the magnetic flux valve and the reluctance of the magnetic circuit containing the magnetic flux valve. As a consequence, the magnetic flux and/or its distribution in the magnetic circuit will change. There is a great potential to use the proposed magnetic flux valve to develop new equipment, such as tunable inductor and adjustable-voltage-ratio transformer for more flexible conversion and control of electric power in many applications. This paper presents the concept, magnetic properties, working principles, and applications of the magnetic flux valve. [ABSTRACT FROM PUBLISHER]

This paper describes a new recovery algorithm for space charge measurement under temperature gradient using the pulsed electro-acoustic (PEA) method. As the temperature difference exists, the density of media becomes inhomogeneous and the waveforms gained by the PEA system are distorted seriously. In this study, the effect of temperature gradient on the acoustic propagation is discussed firstly, and an extended general solution for the acoustic propagation equation is gained. Then, the system transfer function is improved by adding the quadratic approximation to the general solution of the general wave propagation equation. With this new recovery algorithm, the distortion of the waveform can be successfully suppressed. In addition, the PEA waveform recovery method for coaxial cables under temperature gradient is also discussed. [ABSTRACT FROM AUTHOR]

As the temperature gradient always exists in the insulation of power equipment, the influence of temperature gradient on oil-impregnated paper insulation is studied by experiments and simulation. It's found that in the both single-layer and double-layer structures, the heterocharges always appear near the lower temperature electrode, and increase with the enhancement of temperature gradient and field stress, resulting in more considerable field distortion. However, there are more heterocharges in the single-layer samples while the field distortion is more severe in double-layer samples. Numerical simulations were carried out to investigate the mechanism of temperature gradient effect. It is indicated that the space charge accumulation is mainly due to the temperature dependence of the charge injection and conduction. The behavior of interface charges can be well described by assuming an energy barrier for charge transportation at the interface. [ABSTRACT FROM AUTHOR]

Space charge behavior is important in the oil-immersed-paper insulation in converter transformers for HVDC transmission. This paper reports an investigation of the space charge property in samples with two layers of oil-immersed-paper and oil. Based on pulsed electroacoustic (PEA) technique, a waveform recovery method was proposed to get rid of the effects of interface and anisotropy on PEA result, and the space charge distributions in the two-layer samples under different voltage and oil thicknesses were measured. It?s found that the charges with the same polarity as oil side electrode were accumulated at the interface and gradually increased with the increase of applied voltage. However, the positive charge charges always appeared in the oil under positive and negative voltages. Moreover, the charges in samples increased with the increase of applied voltage, while the amount of interface charges decreased with the increase of oil thickness. Due to the existence of interfacial charges, the electrical field in oil-immersed-paper was distorted with its maximum close to the interface. It is indicated that due to the different mobility properties of charges in paper and oil and the interface trap state, the interface between paper and oil plays an important role in charge formation and decay. [ABSTRACT FROM PUBLISHER]