S. M. Lebedev

The breakdown study of three-layer solid dielectrics

The objective of this paper is to study the influence of the lengthening the path of the breakdown channel due to increasing the tangential component of the electric field vector at the interfaces on the breakdown voltage of the laminated dielectrics.

Design and production of large-size thermoplastic products and HV insulation

The results of designing and producing of large-size completed and semi-finished products by the quasi-isothermal method are represented in this paper. Produced large-size products are widely used as the high-quality HV insulation and technological units in various equipments.

Relationship Between the Breakdown Strength and Low-frequency Dispersion of the Complex Permittivity of Polymeric Dielectrics

The relationship between the low-frequency dispersion of the complex permittivity and the breakdown strength of polymeric dielectrics was studied in this work. It was found that the minimum of the voltage-time characteristic of polymeric dielectrics that were studied is related with the dispersion of the complex permittivity. This allows us to predict the dielectric strength of polymeric dielectrics by means of the dielectric spectroscopy method. Good agreement between the experimental results and the model predicted data was found.

Effect of the Mechanical Strain on the Treeing Phenomenon

The influence of the mechanical strain on the tree inception and growth in polymeric dielectrics such as polymethyl methacrylate, polystyrene and polycarbonate was studied in this work. The tree inception and growth process in transparent dielectrics was monitored by the optical method in white and polarized light in the divergent field under AC voltage. It has been found that the tree-inception time and the tree-growth time are dependent on a residual mechanical strain in the vicinity of the needle tip and in the sample volume. The tree inception-time may be increased by means of the control of the mechanical strain in the vicinity of the needle tip. Not only the tree-inception and growth time but also the tree shape depends on residual mechanical strain.

Impulse breakdown strength of irradiated LDPE

The influence of structural inhomogeneities artificially generated by a beam of accelerated protons on the LDPE breakdown under an impulse voltage was investigated in this paper.

Treeing resistance parameters of polymeric dielectrics

Treeing resistance parameters for polystyrene, polymethyl methacrylate, and polycarbonate are presented in this paper. It has been shown that for polymers with residual mechanical strain the greatest treeing resistance is observed for samples with higher tensile yield strength. To decrease the treeing growth rate or increase the breakdown time of polymeric dielectrics, the thermal diffusivity of base polymers should be reduced.

Metal-polymer nano-sized composites and their properties

The main electrical, thermal and morphological properties of polymeric nano-sized composites of polyvinylidene fluoride (PVDF) modified by nanoparticles of Ni have been studied. Properties of nanocomposites can be improved at the optimal filler content compared to those for pure PVDF. For example, the beginning melting temperature and decomposition temperature of these nanocomposites are increased by 5-8°C and 12-21°C respectively. The breakdown strength of PVDF/Ni nanocomposites filled with 0.05-0.1 wt.% of Ni is increased by 5% compared to that for pure PVDF.

Influence of prehistory on properties of PVDF films

Study of the main properties of polyvinylidene fluoride (PVDF) films produced by two processing technologies such as hot pressing from a melt or solution casting was the aim of this paper. To characterize properties of samples, different experimental methods such as FRA (dielectric spectroscopy), IR-spectroscopy and DSC/TGA analysis were used in this work. It was found that the beginning melting temperature, the melting point, the beginning decomposition temperature, and the decomposition temperature for samples prepared by hot pressing method decrease by 8, 2, 10 and 12°C, respectively, compared to those for samples prepared by a solution casting.

Diagnostic of Pre-breakdown State of Polymeric Insulators by the Thermovision Method

The possibility of diagnosing the pre-breakdown state of polymeric insulators by the thermovision method is represented in this paper. The diagnostic method is based on the monitoring of time of the appearance of the local temperature difference and the value of the local temperature difference on the insulator surface due to the defect presence inside the insulator volume. Time corresponding to the critical or pre-breakdown state of dielectric may be estimated by means of above mentioned parameters. Good agreement between the experimental results and the model predicted data was found. The deviation between the experimental results and the model predicted time corresponding to the critical (or pre-breakdown) state of dielectric does not exceed 15%.

Influence of morphology, irradiation and prestressing on the breakdown of LDPE

It is a well-known fact that the breakdown of low density polyethylene (LDPE) depends on the space charge (SC) accumulation in the polymer bulk. In turn, above mentioned process is governed by a submicroscopic structure of polymers, the contact conditions on the interface electrode-polymer and the charge carriers injection from electrodes. It is shown that the surface modification of the LDPE samples by the proton irradiation allows the number of pulses to breakdown to be increased. One more a way for the increase in the lifetime and the breakdown strength of LDPE is the so-called prestressing, i.e., previous polarization of LDPE under DC voltage. It is found that the number of impulses to breakdown is increased more than by a factor of 2.6 and 1.6 at the probability P= 0.05 and P= 0.632 respectively, when an impulse voltage of the same polarity is applied after prestressing of the DC voltage. The number of pulses to breakdown for the irradiated samples is increased by a factor of 9.4 and 3.6 at P=0.05 and P=0.632 respectively, when an impulse voltage of the same polarity is applied after prestressing of the DC voltage. This phenomenon is related with the homo-charge accumulation near the electrodes.