Dielectric behaviour of mineral-oil-based magnetic fluids-the cluster model

Kopčanský, P.; Černák, Jozef; Macko, P.; Spišák, D.; Marton, K.

doi:10.1088/0022-3727/22/9/030

Cited by 20 publications

(12 citation statements)

References 7 publications

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“…The transformer oil-based ferrofluids possess many performance advantages as compared to transformer oils and are summarized as follows [9][10][11][12][13][21][22][23][24][30][31][32][33][40][41][42][43][44]:…”

Section: Advantages Of Transformer Oil-based Ferrofluidsmentioning

confidence: 99%

“…For ferrofluids based on dielectric liquids, the magnetic field includes particle cluster formation that exerts significant influence on the permittivity of the ferrofluid. This phenomenon is called the magnetodielectric effect [9,21,22]. The first magnetic colloid with the aim of liquid insulation was produced to improve the heat transfer from the transformer windings by imposing the magnetic interplay between the field formed by the windings and fluid [23].…”

Section: Introductionmentioning

confidence: 99%

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Study of Dielectric Breakdown Performance of Transformer Oil Based Magnetic Nanofluids

Rafiq

et al. 2017

Energies

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Abstract:Research on the transformer oil-based nanofluids (NFs) has been raised expeditiously over the past decade. Although, there is discrepancy in the stated results and inadequate understanding of the mechanisms of improvement of dielectric nanofluids, these nanofluids have emerged as a potential substitute of mineral oils as insulating and heat removal fluids for high voltage equipment. The transformer oil (TO) based magnetic fluids (ferrofluids) may be regarded as the posterity insulation fluids as they propose inspiring unique prospectus to improve dielectric breakdown strength, as well as heat transfer efficiency, as compared to pure transformer oils. In this work, transformer oil-based magnetic nanofluids (MNFs) are prepared by dispersal of Fe 3 O 4 nanoparticles (MNPs) into mineral oil as base oil, with various NPs loading from 5 to 80% w/v. The lightning impulse breakdown voltages (BDV) measurement was conducted in accordance with IEC 60897 by using needle to sphere electrodes geometry. The test results showed that dispersion of magnetic NPs may improve the insulation strength of MO. With the increment of NPs concentrations, the positive lightning impulse (LI) breakdown strength of TO is first raised, up to the highest value at 40% loading, and then tends to decrease at higher concentrations. The outcomes of negative LI breakdown showed that BDV of MNFs, with numerous loadings, were inferior to the breakdown strength of pure MO. The 40% concentration of nanoparticles (optimum concentration) was selected, and positive and negative LI breakdown strength was also further studied at different sizes (10 nm, 20 nm, 30 nm and 40 nm) of NPs and different electrode gap distances. Augmentation in the BDV of the ferrofluids (FFs) is primarily because of dielectric and magnetic features of Fe 3 O 4 nanoaprticles, which act as electron scavengers and decrease the rate of free electrons produced in the ionization process. Research challenges and technical difficulties associated with ferrofluids for practical applications are mentioned. The advantages and disadvantages linked with magnetic fluids are also presented.

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Section: Advantages Of Transformer Oil-based Ferrofluidsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Study of Dielectric Breakdown Performance of Transformer Oil Based Magnetic Nanofluids

Rafiq

et al. 2017

Energies

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“…Many authors researched the dielectric behavior of ferrofluids, studying mostly the magneto-dielectric effect (i.e., the dependence of dielectric permittivity of a ferrofluid on an applied magnetic field (2,3)). The dielectric relaxation processes within ferrofluids were somehow neglected, only a few papers being published in this field, and no theoretical model was proposed.…”

Section: Introductionmentioning

confidence: 99%

Dielectric Behavior of Some Ferrofluids in Low-Frequency Fields

Mălăescu

Marin

2002

Journal of Colloid and Interface Science

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“…magnetomechanical effects, magnetooptical effects, magneto-dielectric behaviour and so on. The long-chain and cluster models of the magneto-dielectric effect have been analyzed in papers [1,2] for example. It has long been recognized [3] that the presence of foreign particles in liquid insulators has a profound effect on the dielectric breakdown strength of liquids.…”

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confidence: 99%

Dielectric breakdown strength in magnetic fluids

Kopčanský

Tomčo

Marton

et al. 2003

Physica Status Solidi (b)

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The application of an external magnetic field on the magnetic fluids induces needle like structuralization of magnetic particles. The influence of this aggregation of magnetic particles in an external magnetic field H on the magneto-dielectric behaviour and dielectric breakdown strength of a transformer oil based magnetic fluids was measured. The observed decrease of dielectric breakdown strength (for H = 0 and H ⊥ E) vs. distance between electrodes is found to be in agreement with a theory of semi-classical bond percolation for a non-linear composite material. In situation when E  H oscillations of dielectric breakdown strength were observed that are associated with a size effect probably. IntroductionIt is well known that as a consequence of dipol-dipol interaction between magnetic particles in magnetic fluids, magnetic particles tend to attract the neighboring particles in the direction of the magnetic moment. It is expected, therefore, that the magnetic particles will form chains and chain like elongated clusters in which the particles are connected magnetically. Such structural configurations of particles result in many physical properties of magnetic fluids i.e. magnetomechanical effects, magnetooptical effects, magneto-dielectric behaviour and so on. The long-chain and cluster models of the magneto-dielectric effect have been analyzed in papers [1,2] for example. It has long been recognized [3] that the presence of foreign particles in liquid insulators has a profound effect on the dielectric breakdown strength of liquids. In magnetite based magnetic fluids (transformer insulation oil as carrier base for example) the suspended particles are polarizable and are of higher permittivity than the liquid. As a result they experience an electrical force directed towards the place of maximum stress. With uniform field electrodes the movement of particles is presumed to be initiated by surface irregularities on the electrodes which give rise to local field gradients. The accumulation of particles continues and tends to form a bridge across the gap, which leads to the initiation of breakdown [3]. In this sense the motivation of this work was to study the effect of magnetic field induced structuralization of magnetic particles on the dielectric breakdown strength of magnetic fluids.

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Dielectric behaviour of mineral-oil-based magnetic fluids-the cluster model

Abstract: A value of about 20% relative change of the dielectric constant of mineral-oil-based ferrofluids was observed in an external magnetic field. The cluster model, based on a long-chain model, was proposed for the explanation of experimental data.

Cited by 20 publications

References 7 publications

Study of Dielectric Breakdown Performance of Transformer Oil Based Magnetic Nanofluids

Study of Dielectric Breakdown Performance of Transformer Oil Based Magnetic Nanofluids

Dielectric Behavior of Some Ferrofluids in Low-Frequency Fields

Dielectric breakdown strength in magnetic fluids

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