Materials Literature
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Worldwide experience with polymer concrete high-voltage insulators is surveyed. Particular attention is given to the Brazilian experience, the UK initiative, and the introduction of such insulation in India.>
In the classical partial discharge (PD) measuring circuit the current represents the signal that allows the detection of PDs in the tested sample. This current is converted into a voltage by the measuring impedance, amplified, and filtered. The integration process is essential. A standard calibrator for testing integr…
Fast dynamics and accurate control around zero speed are normally required from process technologies. It is from this perspective that the Ward Leonard field control system is described. Several industrial plants utilizing the Ward Leonard control scheme are in use in South Africa. Multiprocessor digital control syste…
An attempt is made to elucidate the mechanisms causing charge accumulation on and inside insulating spacers. The experiments were conducted inside a glass cruciform vessel which could be evacuated to 10/sup -2/ torr and had a maximum SF/sub 6/ working pressure of 2 bar. Cylindrical spacers of polytetrafluorethylene an…
HPAM (partially hydrolyzed polyacrylamide)/chromium acetate and HPAM/phenolic aldehyde colloidal dispersion gels (CDGs) were investigated microscopically using atomic force microscope. The results show that the colloidal dispersion gels eventually form self‐assembly branch‐like fractal structures over a scanning range…
The authors present results of experiments in which LDPE (low-density polyethylene) and/or XLPE (cross-linked polyethylene) specimens were subjected to mechanical vibrations in water or to mechanical vibrations and electric stress combined. Water tree growth experiments in stretched films of XLPE cable insulation are…
The effect of air density on the flashover voltage of polluted high-voltage insulators has been analyzed for AC, DC, and lightning-wave energizations. The findings, based on the physics of the flashover process and test data from representative models and actual insulators, are presented as an altitude scaling factor.…
An online partial discharge test for large steam turbine generators has been developed whereby partial discharges and noise are distinguished on the basis of pulse width. The pulse signals are detected by stator slot couplers (SSCs) which are permanently installed within the generator. Experiments have shown that part…
A series of experiments was conducted on polymeric insulators to examine the role of molecular bond motion in the recovery of hydrophobicity. The samples were also analyzed with characterization techniques which provided important information concerning surface topography, surface hydrophobicity level, and surface che…
Results are presented from analyses of pulses from partial discharges (PDs) in single spherical voids in filled and unfilled epoxy plastic and related to the observed surface deterioration. The filler types used were dolomite, alumina, and silica. Long-time aging tests including pulse phase/height analyses were perfor…
Zinc oxide (ZnO) thin films were accurately and reliably delineated by wet chemical etching in 5% NH/sub 4/Cl in water and by reactive ion etching in a SiCl/sub 4/ plasma. With the etch solution at 55 degrees C, the ZnO etch rate was approximately 300 nm/min. Aluminum, silicon and silicon dioxide were not attacked by…
Sol‐gel processes allow for the synthesis of powders with a more elaborate structure from the point view of composition, purity, size, and size distribution. In the powder case, sol‐gel refers to processing in a liquid medium to obtain a solid, which does not settle under gravity due to the formation of a diffuse netw…
The authors discuss the characterization, evaluation and performance of polymer weathershed materials and insulators used for high-voltage outdoor applications. Ethylene propylene diene monomer (EPDM), ethylene propylene monomer (EPM), silicone rubber (SR), and an EPDM/silicone rubber alloy were tested. The tests cons…
The authors describe experiments which have been designed to study the effect of mechanical strain on the short-term AC breakdown strength of cross-linked polyethylene (XLPE) cable insulation. Laboratory experiments were performed on mechanically stressed Rogowski-type test objects and on sharply bent samples of 12-kV…
The phenomenon of interfacial AC breakdown is considered. Two pieces of EPDM (ethylene-propylene diene monomer) rubber were pressed together and a special jig was conceived to provoke arcing along the interface. The voltage at which breakdown occurred was measured and its dependence on interfacial length and pressure…
An investigation of the pulse propagation characteristics of motor stator windings is reported. The results indicate the effects of electrical and physical length and pulse risetime on the propagation characteristics. They explain the observed phenomena and place them in the context of partial discharge measurement te…
Apical, Upilex, Kapton, Teflon AF, and PEEK polymers are characterized for AC and DC dielectric breakdown in air and in silicone oil at temperatures up to 250 degrees C. The materials are also tested in terms of their dielectric constant and dissipation factor at high temperatures with an electrical stress of 60 Hz, 2…
To elucidate the chemical changes due to dry band arcing, under wet and contaminated conditions, of room temperature vulcanized (RTV) silicone rubber used for coating HV outdoor insulators, the thermal impact of the arcing on the rubber surface was investigated. A loss of hydrophobicity, resulting in a reduction of th…
A series of the bis(octaalkoxyphthalocyaninato)lutetium(III) complexes [(CnO)8Pc]2Lu (n = 10, 12, 14, 16, 18) were synthesized. The mesomorphic behaviour was revealed by using polarization microscopy and DSC. The detailed mesophase structures were clarified by using temperature-dependent X-ray diffraction and temperat…
In this paper, we report the results of the high field magnetization and the high field/high frequency ESR measurements on [Mn III ( taa )], which is a spin-crossover complex. The observed ESR signals will be discussed in connection with the results of our high field magnetization which exhibits the first observation…