Insulation failure of XLPE cable system, particularly in joints and terminations, mostly attributes to local defects resulted from inadequate manufacturing or poor installation workmanship. Since it is well-acknowledged that partial discharge (PD) has a relationship with the discharge source (fault or defect), PD detection and pattern recognition have been widely accepted as a means to provide information on both the type and severity of defects or potential failures, which is further expected to give advice on repair or replacement of cable accessories. This paper presents a laboratory experiment on 110kV XLPE cable joints with artificial typical defects and their partial discharge pattern characteristic. PD patterns and statistical operators of these defects shows dissimilarity, which can be utilized as samples for further on-site PD pattern recognition.
The mechanical and tribological properties of polyimide (PI)-based composites loaded with polytetrafluoroethylene (PTFE) and milled carbon fibers (MCF) in the as received and annealed states were studied in order to increase adhesion to the polymer matrix. It has been shown that loading with micron-range MCF (200 μm) doubles elastic modulus of the composites while all other physical and mechanical properties remain at neat PI levels.
Drawing on self-determination theory, this study examines the relationship between workplace ostracism and deviant behavior by focusing on the mediating role of basic psychological needs and the moderating role of perceived inclusive climate. Findings based on the analysis of 247 valid survey samples suggest that (1) workplace ostracism has a significant positive impact on employees’ deviant behavior; (2) basic psychological needs mediate the relationship between workplace ostracism and employees’ deviant behavior; and (3) employees’ perceived inclusive climate weakens the negative effect of workplace ostracism on basic psychological needs. This study develops new perspectives for workplace ostracism research, extends the factors that influence employees’ deviant behavior, and expands the boundary conditions of organizational difference in self-determination theory. Moreover, these empirical results provide important theoretical guidance to decrease employees’ deviant behavior in organizations.
The structure, mechanical and tribological properties of the polyimide-based composites reinforced with chopped carbon fibers (CCF) and loaded with solid-lubricant commercially available fillers of various natures were investigated. The metal- and ceramic counterparts were employed for tribological testing. Micron sized powders of PTFE, colloidal graphite and molybdenum disulfide were used for solid lubrication. It was shown that elastic modulus was enhanced by up to 2.5 times, while ultimate tensile strength was increased by up 1.5 times. The scheme and tribological loading conditions exerted the great effect on wear resistance of the composites. In the tribological tests by the ‘pin-on-disk’ scheme, wear rate decreased down to ~290 times for the metal-polymer tribological contact and to ~285 times for the ceramic-polymer one (compared to those for neat PI). In the tribological tests against the rougher counterpart (Ra~0.2 μm, the ‘block-on-ring’ scheme) three-component composites with both graphite and MoS2 exhibited high wear resistance. Under the “block-on-ring” scheme, the possibility of the transfer film formation was minimized, since the large-area counterpart slid against the ‘non-renewable’ surface of the polymer composite (at a ‘shortage’ of solid lubricant particles). On the other hand, graphite and MoS2 particles served as reinforcing inclusions. Finally, numerical simulation of the tribological test according to the ‘block-on-ring’ scheme was carried out. Within the framework of the implemented model, the counterpart roughness level exerted the significantly greater effect on wear rate in contrast to the porosity.
The structure, mechanical and tribological properties of the PEI- and PI-based composites reinforced with Chopped Carbon Fibers (CCF) and loaded with commercially available micron-sized solid lubricant fillers of various nature (polymeric-PTFE, and crystalline-Gr and MoS2) were studied in the temperature range of 23–180 (240) °C. It was shown that tribological properties of these ternary composites were determined by the regularities of the transfer film (TF) adherence on their wear track surfaces. The patterns of TFs formation depended on the chemical structure of the polymer matrix (stiffness/flexibility) as well as the tribological test temperatures. Loading with PTFE solid lubricant particles, along with the strengthening effect of CCF, facilitated the formation and fixation of the TF on the sliding surfaces of the more compliant PEI-based composite at room temperature. In this case, a very low coefficient of friction (CoF) value of about 0.05 was observed. For the more rigid identically filled PI-based composite, the CoF value was twice as high under the same conditions. At elevated temperatures, rising both CoF levels and oscillation of their values made it difficult to retain the non-polar PTFE transfer film on the sliding surfaces of the PI-based composite. As a result, friction of the ceramic counterpart proceeded over the composite surface without any protecting TF at T ≥ 180 °C. For the sample with the more flexible PEI matrix, the PTFE-containing TF was retained on its sliding surface, providing a low WR level even under CoF rising and oscillating conditions. A similar analysis was carried out for the less efficient crystalline solid lubricant filler MoS2.
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