Electro-rheological description of liquid and solid dielectrics applied to two-phase polymers: a study of EPDM

Mocellini, Ricardo Raúl

doi:10.1109/tdei.2006.258208

Cited by 10 publications

(23 citation statements)

References 14 publications

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“…It is convenient to comment here, that the connection of the tan() maximum with the melting of the crystalline zones in EPDM was also verified by means of dielectric relaxation (DR) and PALS studies in previous works [19,20,47]. Our results are also in agreement with previous reported works by other authors [32,48].…”

Section: Resultssupporting

confidence: 92%

Influence of empty space and internal stresses on dielectric strength in two-phase polymer

Lambri

Tarditti

Cano

et al. 2013

IEEE Trans. Dielect. Electr. Insul.

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In the present work, a study on the dependence of the Dielectric Strength (DS) as a function of the empty space and the internal stresses into polymer samples has been performed. The empty space was measured by means of positron annihilation lifetime spectroscopy. The internal stresses into the polymer matrix, due to the appearance of the crystalline zones, were determined by applying the inclusion theory results to the dynamic mechanical analysis measurements. Attention to the effect of the chain movement on the electrical breakdown process has been paid. The study has been performed at a mesoscopic scale with the aim of demonstrating the influence of the thermal, mechanical or electrical stresses on the chains movement and their effect on the dielectric breakdown phenomenon. It has been verified that, DS is a function of the empty space into the sample and also of the internal stresses acting at the polymer chains, which result from the crystalline state promoted by chemicrystallization. The empty space decrease and the internal stresses act overlapped against the electrical force operating on the polymer chains. It is deduced from the work, that the precursor phenomenon for the electrical breakdown is the bend of polymer chains, prior to the onset of their collective movement promoted by the electrical forces.Index Terms -EPDM, molecular chain movements, electric breakdown, positron annihilation lifetime spectroscopy, dynamic mechanical analysis.

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Section: Resultssupporting

confidence: 92%

Influence of empty space and internal stresses on dielectric strength in two-phase polymer

Lambri

Tarditti

Cano

et al. 2013

IEEE Trans. Dielect. Electr. Insul.

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“…The model was based on a rheological representation of Voigt type including two or three parameters, defining the so-called elementary unit, Figure 1 [5,10].…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…According to the rheological representation in [5], a solid dielectric contains microscopic permanent dipoles oriented at random, giving rise to a null macroscopic polarization vector (see Figure 2). It is also assumed that the material matrix has an internal structure that allows the orientation of the microscopic dipoles when an external electric field is applied.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…It is also assumed that the material matrix has an internal structure that allows the orientation of the microscopic dipoles when an external electric field is applied. Finally, it is considered that the rotation of the microscopic dipoles does not change their dipolar moments, and that this rotation leads, through a mean-field approximation, to the appearance of compression and tensile effects [5] at the mesoscopic scale, as shown in Figure 2.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…In a recently published work [5] a detailed electrorheological model of the electrical and mechanical response of dielectric materials was presented. The model is based on a Voigt-type rheological representation with two and three parameters.…”

Section: Introductionmentioning

confidence: 99%

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Dielectric properties and viscoelastic response in two-phase polymers

Mocellini

Lambri

Matteo

et al. 2008

IEEE Trans. Dielect. Electr. Insul.

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An electrorheological model is applied to results from Dynamic Mechanical Analysis in order to relate low-frequency dielectric properties to viscoelastic response. The model describes polymers with two phases at the mesoscopic scale, with polar groups embedded in one of the phases. Calculations use an electrorheological representation, based on the Voigt model, to describe the two phases. Low-frequency electrical and mechanical stresses are coupled through the permanent dipole moment of polar groups embedded in one of the phases. In the present model, low-frequency dielectric relaxation is calculated as the superposition of two Debye processes, corresponding to the interaction of the polar groups with the two phases. Induced polarization in the non-polar zones contributes only to highfrequency (relaxed) permittivity. The parameters of the relaxation processes are obtained from the electrorheological model using viscoelastic data from dynamic mechanical analysis. The model was applied to commercial EPDM (ethylene-propylene-diene monomer) employed as housing in electrical insulators rated at 33 kV. This rubber has two phases (amorphous and semi-crystalline), with polar groups embedded in the amorphous phase. Samples aged for 10 years in active transmission lines were studied, and compared with new samples. A good agreement was found between the calculated and measured dielectric spectra, within the low-frequency range where the model is applicable.

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