Fault current limiting system for 500‐kV power systems

Recently, expansion in the scale of power systems and development of localized power sources are leading to an increase in fault current of 500‐kV systems. In the future, it is quite likely that the fault current at the interconnection of such power systems may exceed the rated short‐time current of existing electric power facilities. As one of the solutions of this problem, a thyristor‐controlled series‐resonant‐type fault current limiter (FCL) is proposed to restrain the fault current. This paper deals with the FCL system configuration, the placement method of the FCL in power systems, the outline of the FCL's specification, and the operation method of the protective relay in the multimachine system. Finally, the effectiveness of the FCL is evaluated from the viewpoints of limiting the fault current by simulation analysis. The FCL is shown to be a useful protection device for large, high‐capacity power systems. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 11–22, 1999     

Effect of crystallization temperature of palm oil on its crystallization. IV. The influence of tripalmitoylglycerol (PPP) on the crystallization of 1,3-dipalmitoyl-2-oleoyl-glycerol (POP) and 1,2-dioleoyl-3-palmitoyl-glycerol (POO)

Triacylglycerin in Palm Oil contains POP (1,3-dipalmitoyl-2-oleoyl-glycerol) at 30%, POO (1,2-dioleoyl-3-palmitoyl-glycerol) at 20% and PPP (tripalmitoylglycerol) at 5%. The crystallization temperature of PPP is high and the rates of crystal nuclear formation and growth are fast. It is thus considered that PPP may have some effect on the manner or mode of Palm Oil. Examination was thus made to clarify how PPP may affect the crystallization of POP and POO by differential scanning calorimetry (DSC) and X ray diffractometry (XRD) conducted on PPP/POP and PPP/POO mixtures. High and low temperature peaks were noted to appear on the DSC crystallization curve for either of these mixtures. The high temperature peak was considered possibly due to PPP, and the low temperature peak, to POP or POO. DSC isothermal analysis indicated the rate of crystal growth of either mixture to exceed that of pure of POP or POO. Crystal mixture structure was also seen to be complicated than either compound in pure form. The present findings thus clearly indicate that clarification should be made of the effects of high melting point triacylglycerin, such as PPP, on the crystallization of Palm Oil.     

Site-specific functionalization of proteins by organopalladium reactions

A new carbon-carbon bond has been regioselectively introduced into a target position (position 32 or 174) of the Ras protein by two types of organopalladium reactions (Mizoroki-Heck and Sonogashira reactions). Reaction conditions were screened by using a model peptide, and the stability of the Ras protein under the reaction conditions was examined by using the wild-type Ras protein. Finally, the iF-Ras proteins containing a 4-iodo-L-phenylalanine residue were subjected to organopalladium reactions with vinylated or propargylated biotin. Site-specific biotinylations of the Ras protein were confirmed by Western blot and LC-MS/MS.     

Investigation of tribo-chemistry by means of stable isotopic tracers: Mechanism for durability of monomolecular boundary film

A monomolecular film of octadecanoic acid on a Si(1 0 0) surface was prepared using a computer-controlled Langmuir trough. The tribological properties were acquired by a ball-on-flat type tribo-tester under reciprocating motion. Considerable effects of ball material on lifetime for low friction were observed; a glass ball was excellent while a steel ball was poor. The rubbed surfaces on ball and flat were studied by time-of-flight secondary ion mass spectroscopy. Transfer of the carboxylic acid and silicon onto the ball surface from the flat specimen was found. The role of the transferred acid that prolongs the lifetime of low friction was proposed. It should be emphasized that deuterium-labeled carboxylic acid makes the target of TOF-SIMS analysis clear.     

Fabrication of GaN epitaxial thin film on InGaZnO4 single-crystalline buffer layer

Epitaxial (0001) films of GaN were grown on (111) YSZ substrates using single-crystalline InGaZnO₄ (sc-IGZO) lattice-matched buffer layers by molecular beam epitaxy with a NH₃ source. The epitaxial relationships are (0001)_GaN//(0001)_IGZO//(111)_YSZ in out-of-plane and [112¯0]_GaN//[112¯0]_IGZO//[11¯0]_YSZ in in-plane. This is different from those reported for GaN on many oxide crystals; the in-plane orientation of GaN crystal lattice is rotated by 30° with respect to those of oxide substrates except for ZnO. Although these GaN films showed relatively large tilting and twisting angles, which would be due to the reaction between GaN and IGZO, the GaN films grown on the sc-IGZO buffer layers exhibited stronger band-edge photoluminescence than GaN grown on a low-temperature GaN buffer layer.     

Tribological Characteristics and Tribochemical Reactions of Various Ceramics Lubricated with HFC-134a Gas

The role of tribochemical products in the friction and wear reduction of ceramics with different fractional ionic character in CF₃CH₂F (HFC-134a) gas was investigated using a ball-on-disk type tribometer. Without exposure to air, the wear tracks on the disks were characterized with the aid of a micro-spot X-ray Photoelectron Spectroscope (XPS) whose analytical chamber was connected to the friction chamber of the tribometer. Further, the adsorption and desorption behaviors of HFC-134a molecules on the nascent surfaces of the ceramics were studied using an adsorption test apparatus in high vacuum. It was found that the lubricating effect of HFC-134a gas was closely related to the fractional ionic or covalent characters of the ceramics. HFC-134a gas was more effective in lubricating ionic ceramics than the covalent ceramics. XPS analysis revealed that metal fluorides were mainly formed on the frictional surfaces of the ionic ceramics, whereas the composition of the tribochemical products on the frictional surfaces of the other ceramics was complicated. The adsorption tests proved that HFC-134a was decomposed to an olefin CF₂=CHF on the nascent surfaces of the ionic ceramic Al₂O₃ and the covalent ceramics. However, the formation of organic fluorine-containing compounds was not detected on the frictional surfaces of the ionic ceramics by XPS. This result implies that the mechanism of tribochemical reactions is strongly dependent on the bond type of ceramics. It is concluded that the low friction and wear of the ionic ceramics in HFC-134a gas result from the metal fluorides formed with high surface concentration on the sliding surfaces.     

Investigation of anti-wear additives for low viscous synthetic esters: Hydroxyalkyl phosphonates

Various synthetic esters are widely applied as lubricating fluid to reduce friction and wear at tribological contact. Among them low viscous synthetic esters are expected to improve fuel efficiency by minimizing the fluid friction. These low viscous esters are composed of short-chain fatty acids. Therefore, low viscous synthetic esters are inherently polar molecules. Since efficiency of anti-wear additives decreases with increase of polarity of the base oil, new additive technology is requested.In this work, hydroxyalkyl phosphates [P(O)(OCHRCH₂OH)₃], and hydroxyalkyl phosphonates [P(OH)_n(OCHRCH₂OH)_3−n, where n=1,2] are proposed as novel anti-wear additives for polar synthetic esters. The anti-wear additives are evaluated under the boundary conditions. The additives prevent wear in polar esters, in which conventional anti-wear additives do not work at all. Interestingly, effects of substituent in additive molecule on anti-wear properties are found. Alkyl and aryl derivatives reduce wear remarkably, whereas allyl derivatives exhibit poor results. It is speculated that the anti-wear inefiiciency of allylic compounds is due to auto-oxidation of the additives.A facile preparative method for hydroxyalkyl derivatives characterizes the present additive system. They are prepared in situ by simply mixing phosphonic acid and substituted epoxides. Flexiblity of lubricant design can be made possible by the present additive system.     

Sources of nitrate and ammonium contamination in groundwater under developing Asian megacities

The status of nitrate (NO(3)(-)), nitrite (NO(2)(-)) and ammonium (NH(4)(+)) contamination in the water systems, and the mechanisms controlling their sources, pathways, and distributions were investigated for the Southeast Asian cities of Metro Manila, Bangkok, and Jakarta. GIS-based monitoring and dual isotope approach (nitrate delta(15)N and delta(18)O) suggested that human waste via severe sewer leakage was the major source of nutrient contaminants in Metro Manila and Jakarta urban areas. Furthermore, the characteristics of the nutrient contamination differed depending on the agricultural land use pattern in the suburban areas: high nitrate contamination was observed in Jakarta (dry fields), and relatively lower nutrients consisting mainly of ammonium were detected in Bangkok (paddy fields). The exponential increase in NO(3)(-)-delta(15)N along with the NO(3)(-) reduction and clear delta(18)O/delta(15)N slopes of NO(3)(-) ( approximately 0.5) indicated the occurrence of denitrification. An anoxic subsurface system associated with the natural geological setting (e.g., the old tidal plain at Bangkok) and artificial pavement coverage served to buffer NO(3)(-) contamination via active denitrification and reduced nitrification. Our results showed that NO(3)(-) and NH(4)(+) contamination of the aquifers in Metro Manila, Bangkok, and Jakarta was not excessive, suggesting low risk of drinking groundwater to human health, at present. However, the increased nitrogen load and increased per capita gross domestic product (GDP) in these developing cities may increase this contamination in the very near future. Continuous monitoring and management of the groundwater system is needed to minimize groundwater pollution in these areas, and this information should be shared among adjacent countries with similar geographic and cultural settings.     

Current Pumping from Spin Dynamics

We show theoretically that charge and spin currents arise from spin dynamics in the presence of the spin–orbit interaction. The dominant calculation is the inverse spin Hall effect, namely the spin current pumped from precession of local spins is converted into the charge current by the spin–orbit interaction. The conversion mechanism is explained based on the conservation laws of charge and spin.