A study on condition assessment method of gas‐insulated switchgear. part II. influence of moisture in the SF6, detection of a partial discharge on a spacer,repetition discharge and overheating by incomplete contact

Rationalization of the maintenance of gas‐insulated equipment under operation and lifetime extension based on the results of appropriate diagnosis are necessary to reduce the cost of gas‐insulated equipment. Therefore, condition‐based maintenance (CBM) is required and accurate methods for observing the inside of equipment are important. In this report, we describe a diagnosis method that can be used for actual gas‐insulated equipment, such as to assess the deterioration of the spacers made of epoxy resin and to detect loose connections in the central conductor. The principal results are summarized as follows: (1) The quantity of decomposition gases depends on the moisture and magnitude of the partial discharge. However, decomposition gases were detected even if SF₆ had low moisture content (less than 100 ppm) similar to that used in actual equipment. This means that our method can be applied to actual equipment. (2) It became clear that CF₄ is a typical gas generated by partial discharge on the spacer surface. Therefore, it is possible to diagnose spacer deterioration by monitoring CF₄. (3) Decomposition gases (SF₄, SO₂, SO₄, SO₂F₂) were generated by impulse breakdown, which was assumed to be due to repetition discharge caused by insulation failure and loose connections. (4) SF₆ gas was assumed to be exposed to a loose connection and was heated from room temperature to 800 °C, and the generated decomposition gases were analyzed by FTIR in real time. As a result, the decomposition gases were generated at temperatures above approximately 500 °C in a heating time of 1.5 minutes. Therefore, a loose connection can be detected by analyzing the decomposition gas. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(2): 22–30, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21108     

Low-Temperature Synthesis of β-Ca2SiO4 from Hillebrandite

Experiments on hydrothermal synthesis were conducted using quartz or silicic acid and lime as starting materials at Ca/Si = 2.0. It is possible to synthesize pure hillebrandite (Ca₂(SiO₃)(OH)₂) having the theoretical composition by heating at 200°C for 10 h or at 250°C for 5 h. The synthesized product is fibrous, open at each end, and has a length of 20 to 30 μm. Calcium silicate hydrate gels are produced at the initial stage of the reaction. These react further with the unreacted lime to give hillebrandite. However, when silicic acid is used as silica, hillebrandite with tricalcium silicate hydrate is observed at 250°C because of the high reaction rate of silica. On heating, hillebrandite starts to decompose at about 500°C and produces low-crystalline β-Ca₂SiO₄, which is stable at room temperature and has a remarkably large specific surface area of about 7 m²/g. The decomposition reaction rate in a single crystal is rapid, and the reaction is considered to proceed topotactically.     

Importance of Translation–Replication Balance for Efficient Replication by the Self‐Encoded Replicase

In all living systems, the genetic information is replicated by the self‐encoded replicase (Rep); this can be said to be a self‐encoding system. Recently, we constructed a self‐encoding system in liposomes as an artificial cell model, consisting of a reconstituted translation system and an RNA encoding the catalytic subunit of Qβ Rep and the RNA was replicated by the self‐encoded Rep produced by the translation reaction. In this system, both the ribosome (Rib) and Rep bind to the same RNA for translation and replication, respectively. Thus, there could be a dilemma: effective RNA replication requires high levels of Rep translation, but excessive translation in turn inhibits replication. Herein, we actually observed the competition between the Rib and Rep, and evaluated the effect for RNA replication by constructing a kinetic model that quantitatively explained the behavior of the self‐encoding system. Both the experimental and theoretical results consistently indicated that the balance between translation and replication is critical for an efficient self‐encoded system, and we determined the optimum balance.     

Ring‐opening metathesis polymerization of norbornene catalyzed by tantalum and niobium complexes with chelating O‐donor ligands

BACKGROUND: In comparison with group 6 transition metals, such as tungsten and molybdenum, and group 8 metal ruthenium, group 5 metal‐based catalysts for ring‐opening metathesis polymerization (ROMP) have remained much less studied. The few reported ROMP catalysts of group 5 metals require multiple reaction steps to be synthesized, and are highly sensitive to air and moisture. RESULTS: A series of pentavalent tantalum and niobium complexes having catecholato, tropolonato, hinokitiolato, biphenolato and binaphtholato ligands were prepared and their catalytic activities for the ROMP of norbornene (NBE) were studied in the presence of trialkylaluminium as a co‐catalyst. Among these complexes, the tantalum complexes showed high activity upon activation with Buⁱ₃Al. In sharp contrast, the niobium complexes were effectively activated with Me₃Al. The polymers obtained with these complexes had high molecular weights (M_n > 10⁵ g mol⁻¹) and relatively narrow molecular weight distributions (M_w/M_n ≈ 2). CONCLUSION: We found that easily accessible and relatively stable tantalum and niobium complexes with such chelating O‐donor ligands showed high catalytic activity for ROMP of NBE depending on the kind of co‐catalyst. These findings could contribute to future development of ROMP catalysts. Copyright © 2008 Society of Chemical Industry