Search

AbstractWe prove the uniformity of the in-plane and anti-plane elastic field of stresses and strains inside an incompressible nonlinear elastic elliptical inhomogeneity embedded in an infinite linear isotropic elastic matrix subjected to uniform remote in-plane and anti-plane stresses. The elastic material occupying the elliptical inhomogeneity obeys Neuber’s special nonlinear stress-strain law. The original boundary value problem is finally reduced to a single non-linear equation for the constant effective strain within the inhomogeneity, which is rigorously proved to have a unique solution. Once the non-linear equation is solved numerically, we establish the uniform elastic field within the elliptical inhomogeneity and the non-uniform elastic field in the linear elastic matrix. [ABSTRACT FROM AUTHOR]

We discuss an exactly solvable relativistic model of a nonrelativistic linear harmonic oscillator in the presence of a constant external force. We show that as in the nonrelativistic case, the relativistic linear oscillator in an external uniform field is unitarily equivalent to the oscillator without this field. Using two methods, we calculate transition amplitudes between energy states of the discrete spectrum of the relativistic linear oscillator under the action of a suddenly applied uniform field. We find Barut–Girardello coherent states and the Green's function in the coordinate and momentum representations. We obtain the linear and bilinear generating functions for the Meixner–Pollaczek polynomials. We prove that the relativistic wave functions, the generators of the dynamical symmetry group, and the transition amplitudes have the correct nonrelativistic limit. [ABSTRACT FROM AUTHOR]

In the work, dual electroinductive spherical sensors, which are a constructive combination of two double sensors into one, are subjected to experimental studies in a non-uniform electric field. Dual sensors are an integral part of a new method for measuring inhomogeneous electric fields by average value. Experimental studies are aimed at confirming the possibility of using dual sensors in inhomogeneous electric fields and the method of measuring the electric field strength by the average value. To carry out experiments in a non-uniform electric field, a high-voltage measuring setup is created. The measuring setup made it possible to obtain the static characteristics of a dual sensor in an inhomogeneous electric field. Comparison of the static characteristics obtained in a homogeneous and inhomogeneous field makes it possible to estimate their errors and compare these errors with theoretically calculated ones. The comparison results have showed that the discrepancy between the static characteristics does not exceed +1,5 %, and the discrepancy in the errors of the dual sensor, estimated from experimental data in an inhomogeneous field and obtained theoretically, does not exceed ±2 % in absolute units. The obtained research results allow us to confirm the adequacy of the theory underlying the theoretical provisions laid down in the calculations of dual electric induction spherical strength sensors of the electric field.

With the aid of conformal mapping and analytic continuation, we prove that within the framework of anti-plane elasticity, a non-parabolic open elastic inhomogeneity can still admit an internal uniform stress field despite the presence of a nearby non-circular Eshelby inclusion undergoing uniform anti-plane eigenstrains when the surrounding elastic matrix is subjected to uniform remote stresses. The non-circular inclusion can take the form of a Booth's lemniscate inclusion, a generalized Booth's lemniscate inclusion or a cardioid inclusion. Our analysis indicates that the uniform stress field within the non-parabolic inhomogeneity is independent of the specific open shape of the inhomogeneity and is also unaffected by the existence of the nearby non-circular inclusion. On the other hand, the non-parabolic shape of the inhomogeneity is caused solely by the presence of the non-circular inclusion. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Medical Equipment Journal is the property of Chinese Medical Equipment Journal Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article presents a hybrid optimal design of biplanar coils, which produce uniform fields and field gradients. It treats the coil design issue as a nonlinear programming problem, and seeks the best performance via the optimal algorithm. The target field method is first utilized to obtain the initial coefficients and ranges of searching areas in stream functions. Then, the magnetic field relative error is defined as the fitness function for minimization, and the particle swarm optimization algorithm is adopted to optimize the aforementioned coefficients. It not only overcomes the dependence on the position distribution of target field points, but also reduces the required computational dimensions without affecting the pursuit of the ultimate performance. Comparing this work with the traditional target field method, the field inhomogeneity error in the region of interest is reduced from 6.55% to 0.95% ($B_x$ coil), 12.02% to 0.35% ($B_z$ coil), 16.54% to 0.57% ($\mathrm{d}B_x/\mathrm{d}z$ coil), and 11.8% to 0.28% ($\mathrm{d}B_z/\mathrm{d}z$ coil). Numerical simulation and experimental results show the validity and significance of the proposed method. It has great improvements in both uniform fields and field gradients, which is beneficial to the perfect realization of nulling undesired magnetic fields. [ABSTRACT FROM AUTHOR]

The article provides a comparative analysis of multi-element sensors of an electric field of a flat shape differing in various configurations of sensitive elements, each of which is determined by its design parameters. For this, a generalized mathematical model of the sensor is compiled taking into account its design parameters which affect the error from field inhomogeneity and the spatial range of measurement. Using a generalized mathematical model, graphs of the sensor error are constructed depending on the spatial measurement range and various design parameters of its sensitive elements. The change in design parameters allowed us to model sensitive elements in the form of quadrants and truncated quadrants of a circle. According to the error graphs, it is established that sensitive elements made in the form of quadrants of a circle provide the sensor with a lower error and a larger spatial range of measurement, therefore their use is more appropriate. The studies performed allowed us to obtain the following technical results. Sensors with sensitive elements in the form of a quadrant of a circle have a minimum of an error and a maximum of a spatial range of measurement at design parameters: b = 0 and b0 = 0,2; b = 0 and b0 = 0.4, for which, with a maximum spatial range of measurement equal to unity (a = 1), the errors are respectively minus 3 % and minus 10 %.

An exactly solvable relativistic model of a linear oscillator is considered in detail in the presence of a constant external force in both the momentum representation and the relativistic configuration representation. It is found that in contrast to the nonrelativistic case, depending on the magnitude of the force, both discrete and continuous energy spectra are possible. It is shown that in the case of a discrete spectrum, the wave functions in the momentum representation are expressed in terms of the Laguerre polynomials, and in the relativistic configuration representation, in terms of the Meixner–Pollaczek polynomials. Integral and differential–difference formulas are found connecting the Laguerre and Meixner–Pollaczek polynomials. A dynamical symmetry group is constructed. [ABSTRACT FROM AUTHOR]

We rigorously prove that a non-elliptical inhomogeneity continues to permit an internal uniform stress field despite the presence of a nearby non-circular Eshelby inclusion undergoing uniform anti-plane eigenstrains when the surrounding matrix is subjected to uniform remote anti-plane stresses. Here, we adopt a specific representation of the non-circular Eshelby inclusion as a Booth's lemniscate inclusion. Our analysis indicates that the internal uniform stress field inside the non-elliptical inhomogeneity is independent of the existence of the Booth's lemniscate inclusion whereas the non-elliptical shape of the inhomogeneity is attributed entirely to its presence. Representative numerical examples are presented to demonstrate the feasibility of the proposed method of general solution. [ABSTRACT FROM AUTHOR]

The electric field uniformity imposes a significant effect on the breakdown mechanisms of dielectric liquids. In general, breakdown is dominated by streamer initiation under uniform field, while it is dominated by streamer propagation under non-uniform field. This paper presents a study on identifying and quantifying the transition field factor boundary, represented by the field enhancement factor ƒ, between the two dominating breakdown mechanisms. The methods for deducing the transition field factor boundary are introduced. The first method from our previous study was developed by measuring and processing both the streamer initiation and breakdown voltages. In this paper, a new method is developed by only processing the breakdown voltage data. Based on the breakdown results reproduced from the literature, the transition field factor boundaries are derived for the mineral oil under both positive and negative lightning impulses. It is found that the negative transition field factor boundary is lower than the positive one. A four-region model is proposed to describe the effect of impulse polarity on breakdown mechanisms of dielectric liquids and to interpret the transition of breakdown mechanisms with respect to the field uniformity. [ABSTRACT FROM AUTHOR]

The article examines a multi-element flat sensor of the components of the intensity vector of a low-frequency electric field manufactured using new technologies and capable of being integrated into modern gadgets. The sensor is suitable for measuring the intensity of electric fields adversely affecting a person. In this regard, the problem solved in the article is relevant. The research results allowed to create such a sensor evaluate its metrological characteristics and establish their dependence on the degree of homogeneity of the electric field. The established interrelation between the sensor error and the degree of heterogeneity of the electric field allows determining the spatial measurement range by a given error or by setting a sensor for a given spatial measurement range. For example, a 2 % sensor error corresponds to the spatial measurement range a determined by the distance from the field source from 0 M to 7 M (a = 0,15), where M is the linear size of the sensor.

We develop a criterion for spark-breakdown in non-uniform field geometries with positive polarity and small electrode separations so that breakdown evolves without the formation of a leader. We arrive at the spark-breakdown criterion by framing it in terms of gain and instability conditions, whose relative importance is established from an analysis of the experimental breakdown characteristics and correlations with streamer behavior in short gaps. Results are presented in the context of two generic geometries having coaxial and point-plane electrodes. For nearly uniform field situations, we re-confirm that the breakdown criterion obtained by the usual extension of either the Townsend or Meek criteria satisfactorily predicts the experimental results. On the other hand, for increasing non-uniformity, the results for the corona and spark branches of the breakdown characteristics are shown inconsistent with a breakdown criterion solely based on either the Townsend or streamer mechanisms. In particular, the avalanche gain factor, the primary component of the Townsend and streamer criteria, does not determine the spark breakdown criterion. Streamers can cross the gap for a significantly wide range of applied voltages without triggering a spark. We find that it is the instability condition, derived from a relation between the minimum Laplacian field in the gap and the local streamer body field (which we relate to the streamer sustaining field), that is sufficient for determining the spark threshold thereby yielding a breakdown criterion. [ABSTRACT FROM AUTHOR]

Using the sextic Stroh formalism, we show that the strains and stresses inside an anisotropic elastic parabolic inhomogeneity are uniform when the surrounding anisotropic elastic matrix is subjected to uniform loading at infinity. All of the uniform strains and stresses inside the inhomogeneity are independent of the single geometric parameter characterizing the two-phase structure. In addition, some strain and stress components within the inhomogeneity simply coincide with their remotely prescribed counterparts in the matrix. [ABSTRACT FROM AUTHOR]

We use conformal mapping techniques and analytic continuation to prove that the stress field inside a non-parabolic open inhomogeneity embedded in a matrix subjected to uniform remote anti-plane stresses can nevertheless remain uniform despite the presence of a screw dislocation in its vicinity. Furthermore, the internal uniform stresses inside the inhomogeneity are found to be independent of both the shape of the inhomogeneity and the presence of the screw dislocation. On the other hand, we find that the existence of the nearby screw dislocation exerts a significant influence on the non-parabolic shape of the inhomogeneity. [ABSTRACT FROM AUTHOR]

We establish the uniformity of the internal in-plane elastic field of stresses and strains inside an incompressible nonlinear elastic elliptical inhomogeneity embedded in an infinite linear isotropic elastic matrix subjected to uniform remote in-plane stresses. The nonlinear elastic material occupying the inhomogeneity can incorporate a power-law hardening material. The original boundary value problem is ultimately reduced to a single non-linear equation. It is proved rigorously that the non-linear equation has a unique solution. Once the non-linear equation is solved numerically, the uniform elastic field within the nonlinear elastic elliptical inhomogeneity and the non-uniform elastic field in the linear elastic matrix can be determined. • Incompressible nonlinear elastic elliptical inhomogeneity in isotropic matrix. • Uniformity of the internal in-plane elastic field of stresses and strains. • Elastic material in inhomogeneity can incorporate a power-law hardening material. • Uniform elastic field in the inhomogeneity and elastic field in matrix determined. [ABSTRACT FROM AUTHOR]

This paper reports on an investigation into the surface flashover of an insulator in a C4F7N/CO2 mixture which is used as an alternative to SF6. To date, no studies on this aspect have been reported in the literature. This study was done for a uniform field using a 220 kV AC experimental platform. The influence of molar fraction, gas pressure and creepage distance is reported and compared to that in SF6. The results show that small quantities of C4F7N mixed in CO2 can increase the surface flashover voltage but, as the fraction of C4F7N increases, saturation of the surface flashover occurs. The relative surface flashover voltage of 13.0% C4F7N/87.0% CO2 is approximately 80% that of SF6. The empirical formulae on the critical flashover electrical field has been obtained, which may be referenced in the design of environment friendly high voltage equipment. [ABSTRACT FROM AUTHOR]

Cavity resonators are often used for electron paramagnetic resonance (EPR). Rectangular TE102 and cylindrical TE011 are common modes at X-band even though the field varies cosinusoidally along the Z-axis. The authors found a way to create a uniform field (UF) in these modes. A length of waveguide at cut-off was introduced for the sample region, and tailored end sections were developed that supported the microwave resonant mode. This work is reviewed here. The radio frequency (RF) magnetic field in loop-gap resonators (LGR) at X-band is uniform along the Z-axis of the sample, which is a benefit of LGR technology. The LGR is a preferred structure for EPR of small samples. At Q-band and W-band, the LGR often exhibits nonuniformity along the Z-axis. Methods to trim out this nonuniformity, which are closely related to the methods used for UF cavity resonators, are reviewed. In addition, two transmission lines that are new to EPR, dielectric tube waveguide and circular ridge waveguide, were recently used in UF cavity designs that are reviewed. A further benefit of UF resonators is that cuvettes for aqueous samples can be optimum in cross section along the full sample axis, which improves quantification in EPR spectroscopy of biological samples. [ABSTRACT FROM AUTHOR]

In order to standardize and complete the radiated interference E-field threshold testing in reverberation chambers proposed previously, the influence factors on the measurement accuracy were analyzed in this paper, obtaining the error variation with different test conditions. It is revealed that the electrical size of the equipment under test (EUT) is the main restricted factor to the application range of the proposed method. Decreasing the electrical size of the EUT, an experiment was implemented to study the influence of the electrical size on measurement accuracy. The result shows that the measurement error can be decreased to less than 3 dB when the testing factors are reasonably chosen and the electrical size of the EUT is large enough. However, when the electrical size of the EUT is too small, the measurement uncertainty level may be larger than 3 dB. Accordingly, the proposed method is more proper for the EUTs with large electrical sizes. [ABSTRACT FROM AUTHOR]

Efficiency of high frequency surface wave radars may be improved by inserting a metamaterial in the vicinity of transmitting antennas that will reinforce the propagation of surface waves. This paper deals with the first and second order derivations of the surface impedance boundary conditions (IBC) applied to model such a metamaterial, which is equivalent to a bounded ground with a low negative permittivity. The goal of this paper is to extend an approach previously based on the classical Leontovich IBC which is usually restrained to high permittivity grounds. As shown here, a simplification in the expression of the surface impedance is possible in the case of a planar and homogeneous surface. That allows to have a first order impedance boundary condition substituted for the required second order impedance boundary condition. [ABSTRACT FROM AUTHOR]

The spatial distribution of the magnetic flux density ( B ) was determined for the passive sources of magnetic field most used in magnetic stimulation of biological systems, toroidal dipole magnets and cylindrical dipole magnets, in order to find the spatial characteristics of the magnetic field within the volumes of interest for the treatment of biological systems. The perpendicular and parallel components of B regarding the polar surface of the magnets were measured, for which a FW Bell 5180 digital teslameter was used with longitudinal and transverse probes and a two-dimensional positioning system with millimeter scale. It was found that the magnets of this type, which are the most used, present a strong variation of the magnitude and direction of the magnetic flux density for spaces specified in millimeters, reason why the homogeneity of the magnetic field in the regions of interest was found to be relatively low, which makes them elements with a strong applicability for the stimulation of biological systems in which magnetic field gradients up to mT/mm are required in the case of cylindrical magnets, and up to tens of mT/mm in the case of toroidal magnets. Finally, it is concluded that a high percentage of experiments reported in the literature on magnetic treatment of biological systems may be presenting values of B in their doses with deviations of more than 100% of the real value, which raises an incongruence in the cause-effect proposed relation. [ABSTRACT FROM AUTHOR]

A magnetic fluid drop immersed in oil and exposed to a harmonic electric field is studied theoretically. All surface charge transportations are considered. It is shown that the surface conductivity can quantitatively change the deformation, but cannot change it qualitatively. [ABSTRACT FROM AUTHOR]

Our experimental study has shown that whereas the application of a uniform magnetic field can significantly intensify heat transfer in ferrofluids, in general, it is a nonmonotonic function of the strength of the applied magnetic field. [ABSTRACT FROM AUTHOR]

Radio frequency and microwave heating of dielectric objects is often susceptible to an excessive temperature spread due to uneven energy deposition. The exposure to a non-uniform field is a well-studied cause for this difficulty encountered in numerous applications. There are, however, some less-understood causes, which are inherent in nature in that they persist even in a perfectly uniform field. We present an experimental study on three main inherent causes with rice grains as samples. Experiments are conducted in an applicator, in which samples are irradiated by a 24 GHz microwave. High radiation uniformity (~99%) and polarization control allow a quantitative examination of each cause. Their individual and collective effects are found to be highly significant. In particular, polarization-charge shielding alone can result in a temperature spread of ~18.2% for the samples examined. Physical interpretations are given and an effective method for its mitigation is demonstrated. [ABSTRACT FROM AUTHOR]

The hysteresis properties of electrical steel sheet (ESS) is very helpful to develop new type electrical machines and improve their performance. Therefore, two-dimensional steel sheet tester (SST) is required to measure the hysteresis properties of ESS. This paper introduces a kind of square type SST, but this SST can only measure the non-oriented and grain-oriented ESS because the size of the specimen is not large enough. To measure highly grain-oriented ESS, a new round type SST which is designed to have broader region of uniform field and allows a larger specimen is proposed in this paper. Meanwhile, magnetostriction properties also can be measured by this round type SST. [ABSTRACT FROM AUTHOR]

A “distributed inductor” comprises a core containing multiple winding windows carrying prescribed Ampere-turns. Its magnetic field can be shaped to vary by less than a distribution factor υ. The positions, dimensions, and Ampere-turns of the windings are synthesized to improve the energy density. A design procedure is formulated to accentuate the impact of υ on the tradeoffs between inductance and losses. It is validated by a prototype having half the height of the commercial counterpart for a 30 W converter. [ABSTRACT FROM PUBLISHER]

The Wiener index of a hypergraph is the sum of distances between all pairs of vertices of the hypergraph. In this paper, we first investigate the Wiener index of some special r-uniform paths and r-uniform cycles. The Wiener index of different kinds of 3-uniform paths were also considered. Then we explore the lower bound of Wiener index in a r-uniform hypergraph on n vertices with a given circumference which is the maximum length of a cycle in a hypergraph. In the last part, we propose the concept of the chemical bond-Wiener index of a graph, which is the sum of the distances between all pairs of chemical bonds of a graph, considering the removing of hydrogen atoms. The polyphenyl chains with minimum and maximum chemical bond-Wiener indices among all the polyphenyl chains with h hexagons were completely determined. [ABSTRACT FROM AUTHOR]

We address the question whether quantum probes in a gravitational field can be considered as test particles obeying the weak equivalence principle (WEP). A formulation of the WEP is proposed which applies also in the quantum regime, while maintaining the physical content of its classical counterpart. Such formulation requires the introduction of a gravitational field not to modify the Fisher information about the mass of a freely-falling probe, extractable through measurements of its position. We discover that, while in a uniform field quantum probes satisfy our formulation of the WEP exactly, gravity gradients can encode nontrivial information about the particle’s mass in its wavefunction, leading to violations of the WEP. [ABSTRACT FROM AUTHOR]

The field impulse voltage test plays the most important role to ensure the safe of the power transformer. It is hard to carry out the standard impulse voltage test for the power equipment because the generator is very huge. The oscillating impulse voltage waveform has high efficiency and be recommended by IEC 60060-3 as the field test waveform. Transformer oil is the main insulation part of power transformer insulation system. The insulation characteristics of transformer oil under different type impulse waveform have great influence to the design, operation and test amplitude for the power transformer. This paper focuses on the breakdown characteristics of transformer oil in a uniform field under oscillating impulse voltage (OIV). Three type oscillating impulse voltage waveforms with oscillating frequency of 14, 117 and 373 kHz were adopted as the test waveforms. The standard lightning impulse (SLI) voltage was also adopted as the reference waveform. The experiment results show the breakdown waveforms have large oscillation under OIV but little oscillation under SLI for the influence of circuit inductor. The minimum breakdown voltage increase with the increase of oscillating frequency and the 117 kHz impulse waveform has the similar breakdown voltage with SLI waveform. The voltage-time distributions were obtained through lab test and the results shown that the OIV have the longer time lag than SLI for the influence of the oscillation of waveform. The experimental results were explained through streamer mechanism. The study provides the foundation for the field impulse test using oscillating impulse waveform. [ABSTRACT FROM PUBLISHER]

A low-profile, beam tilted microstrip patch antenna (MPA) with broad-useful bandwidth and improved gain is presented. The proposed design comprises of a rectangular MPA and a square-loop unit-cell-based metasurface superstrate with different effective refractive index regions. The beam tilting is achieved by the phenomenon of phase difference produced by the superstrate having different refractive index regions. The experimental results display a maximum beam tilt of 27° in the E-plane at 5 GHz with a slight frequency dependability of 0.013°/MHz. The proposed design also offers a broad-useful bandwidth of 11% centred at 4.82 GHz, while maintaining relatively low antenna height of 0.06λ. Moreover, uniform field distribution due to superstrate provides a maximum gain of 8.4 dBi with a variation ≥1.3 dB. [ABSTRACT FROM AUTHOR]

For constitutive modeling of WC hardmetals we used a full field finite element simulations of accurately reproduced scanning electron microscope images and a simple uniform field two-phase model. Both models combine isotropic Drucker–Prager elastic–plastic behavior of WC grains and isotropic von Mises elastic–plastic behavior of the binder, and include non-linear hardening. We performed simulations for representative volume elements using the generalized 2.5D formulation and demonstrated a good agreement between the two models in terms of the effective mechanical behavior. Effective elastic properties and coefficients of thermal expansion were obtained. Effective yield stresses evaluated at 0.1% of effective plastic strain were also computed for six different loading paths. Probability and joint probability histograms obtained in FE simulations are presented. We also studied the effect of residual thermal stresses, which appear in WC hardmetals due to cooling from sintering temperatures. Finally, we obtained a realistic yield surface for a three-dimensional microstructure using a uniform field model with spherical inclusions. This surface combines a Drucker–Prager region for moderate pressures and a von Mises region for high pressures, with a sharp transition between these two regions. Four different WC hardmetal grades were considered. In total, nine microstructures were reproduced in finite element models with the binder content ranging from 10% to 19%. A sensitivity study on the binder plastic properties was carried out, thus the obtained results for the yield surface are applicable to real hardmetals with different binder materials and various binder content. [ABSTRACT FROM AUTHOR]

This paper constructs multiple elastic inclusions with prescribed uniform internal strain fields embedded in an infinite matrix under given uniform remote anti-plane shear. The method used is based on the sufficient and necessary conditions imposed on the boundary values of a holomorphic function, which guarantee the existence of the holomorphic function in a multiply connected region. The unknown shape of each of the multiple inclusions is characterized by a polynomial conformal mapping with a finite number of unknown coefficients. With the aid of Cauchy's integral formula and Faber series, these unknown coefficients are determined by a system of nonlinear equations. Detailed numerical examples are shown for multiple inclusions with various prescribed uniform internal strain fields, for symmetrical inclusions and for inclusions whose shapes are independent of the remote loading, respectively. It is found that the admissible range of uniform internal strain fields for multiple inclusions is moderately larger than the admissible range of the uniform internal strain field for a single elliptical inclusion under the same remote loading. In particular, specific conditions on the prescribed uniform internal strain fields and elastic constants of the multiple inclusions are derived for the existence of symmetric inclusions and rotationally symmetrical inclusions. Moreover, for any two inclusions among multiple inclusions of shapes independent of the remote loading, it is shown that the ratio between the uniform internal strain fields inside the two inclusions equals a specific ratio determined by the shear moduli of the two inclusions and the matrix. [ABSTRACT FROM AUTHOR]

This paper studies wave propagation in a poroelastic solid bar with polygonal cross-section under plane-strain conditions. The boundary conditions on the surface of the cylinder whose base curve is polygon are satisfied by means of the Fourier expansion collocation method. The frequency equations are discussed for both symmetric and antisymmetric modes in the framework of Biot's theory of poroelastic solids. For illustration purposes, sandstone saturated materials and bony material are considered. The numerical results were computed as the basis of relevant material data. Phase velocity is computed against the wavenumber for various cross-sections and results are presented graphically. [ABSTRACT FROM AUTHOR]

This paper presents a study of the lightning breakdown voltages of Palm Oil (PO) and Coconut Oil (CO) under a non-uniform field with consideration on the polarity effect at various gap distances. All tests were carried based on a needle-sphere electrode configuration and various gap distances ranging from 2 to 25 mm under positive and negative voltage polarities. Three different testing techniques were used in this study including rising-voltage, up-and-down and multiple-voltage methods. The PO used in this study was Refined, Bleached and Deodorised Palm Oil (RBDPO) Olein. Three different samples of RBDPO and one sample of CO were tested. The Weibull distribution was used as a statistical approach to determine the withstand voltages of all samples at 1% and 50% probabilities for each type of oil. Under positive voltage polarity, it was found that the 50% breakdown voltages of RBDPO and CO were comparable with Mineral Oil (MO) whereby the highest percentage of difference among all gap distances was less than 15%. RBDPO and CO have lower 50% breakdown voltages than MO under a negative lightning impulse for which the highest percentage of difference can be up to 40%. [ABSTRACT FROM AUTHOR]