Yu.P. Pokholkov

The barrier effect in three-layer solid dielectrics in quasi-uniform electric field

In this paper, the experimental results of the study of the behaviour of three-layer solid dielectrics in high electric field are presented. The breakdown voltage and the breakdown channel forms depend on factors such as the position of the boundaries between layers in the gap, the ratio of permittivities of layer materials, and the homogeneity of barrier materials. It was found that polarization plays the main role in the barrier effect.

Tree-inception in PMMA with a barrier

The experimental results of a study of the tree-inception phenomenon for three-layer dielectrics in a divergent field are presented in this paper. It is shown that the tree-inception time depends on both the position of the high-permittivity barrier in the insulating gap and the ratio of the permittivities of the barrier material and main dielectric, and that it has a maximum at the optimal barrier position. It is found that the tree-inception length has a minimum value at this barrier position. Good agreement between the coefficient of the local field non-uniformity and the tree-inception time or the initial tree length was found.

Effect of Ultrasonic Compaction of Nanopowder on Structure and Fracture Character of Zirconia Nanoceramics

The structural-scale hierarchy and phase composition of zirconia nanoceramics (ZrO2 — 5.4wt%Y2O3) fabricated from plasma chemical zirconia nanopowder compacted by ultrasonic (US) action and without it are studied and compared. It has been shown, that US-action is rather effective method in technological process of nanoceramics production. It involves a reduction of grain sizes and grain aggregate sizes of sintered ceramics; the grain in such ceramics is a layered pack of subgrains, nuclei of which are the scaly particles of initial nanostructured powder (NP). The ceramics consists of cubic and tetragonal phases of zirconia

Influence of high-permittivity barriers on PD activity in three-layer dielectrics

It is a well-known fact that the breakdown voltage of dielectrics in a divergent field may be increased by using an additional insulating layer (a barrier) placed at the optimal position between the electrodes. This paper is devoted to the investigation of the barrier effect in solid dielectrics in a quasi-uniform electric field, i.e. the study of the relationship between partial discharge (PD) activity and the barrier position in the insulating gap. It is established that the PD parameters depend on the barrier position in the gap. In particular, the ignition voltage of critical PDs is increased by more than 50% at the optimal barrier position compared to that for other barrier positions.

The use of the ultrasonic compaction method for the PZT piezoelectric ceramics fabrication

The method of ultrasonic (US) compaction for the fabrication of Pb(ZrTi)O/sub 3/ PZT piezoceramics was approved. The values of density, granularity, shrinkage of ceramic samples, sintered from the compacts compacted by traditional uniaxial pressing and by ultrasound action are compared. It is shown that US compaction contributes to sintering temperature lowering and to PZT piezoceramics granularity reduction.

Influence of applied oscillation mode at nanopowder ultrasonic compaction on Y-TZP nanoceramics properties

The properties of the green compacts from (ZrO/sub 2/-5% Y/sub 2/O/sub 3/) ultrafine powders (UFP) compacted under action of ultrasonic oscillations (USO), which were supplied perpendicularly and parallel to pressing axis have been studied. The distinctions of such properties as density, granularity, hardness and fracture toughness of ceramics sintered from the compacts of both types are shown.

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.

Frequency spectrum of dielectric strength of PET

It is a well-known fact that the breakdown voltage of a dielectric at the same thickness depends on a rate of increase of the applied voltage. At some rate of increase of voltage a minimum of either the voltage-time characteristic or the dielectric strength are usually observed. This effect is very important from the practice for the choice of the optimal frequency range of dielectrics being used in HV designs. In this work the testing results of the voltage-time characteristic study for PET film are represented. PET is usually used as HV insulation of various electrical engineering equipment. The role of the frequency dispersion of the complex permittivity in the appearance of minimum in the voltage-time characteristic or the dielectric strength of PET films was discussed.

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.