Tadao Minagawa

Analysis of PD-generated SF/sub 6/ decomposition gases adsorbed on carbon nanotubes

Chemical byproducts analysis has been recognized as a powerful diagnosis method for SF6 gas-insulated switchgear (GIS). The authors have previously demonstrated that a carbon nanotube (CNT) gas sensor could detect partial discharge (PD) generated in SF6 gas. However, PD-generated decomposition gas species, which were responsible for the CNT gas sensor response, have not been identified yet. In this paper, two kinds of experiments were conducted in order to identify the responsible decomposition gas species. At first, the decomposition gas molecules adsorbed on CNTs were analyzed by Fourier transformation infrared (FTIR) spectroscopy. FTIR absorbance was observed around 735 cm-1 after CNTs were exposed to PD generated in SF6. In the second experiment, the CNT gas sensor responses to typical SF6 decomposition products (HF and SF4) were examined. The CNT gas sensor responded to these gases in the same way as to PD generated in SF6. SF4 response was larger than HF response. Based on these results, SF 4 and SOF2 emerged as candidates for the responsible decomposition gases. Electrochemical interactions between adsorbed gas molecules and CNT were discussed based on theoretical predictions of molecular orbital calculations. The calculation results suggested that both of SOF2 and SF4 could increase the CNT gas sensor conductance

Development of SF6 decomposition gas sensor

Abstract Gas sensors for detecting SF6 decomposition products have been pursued as low-cost instrumentation for detecting and locating faults in gas-insulated switchgear (GIS). We have developed an amperometric solid-state ionic sensor using fluorine ion-conductive solid electrolyte. In order to improve its sensitivity, the surfaces of the electrolyte are roughened by sandblasting, and are covered with the gas permeable Au electrodes. The roughness of the surfaces and the thickness of the electrodes are optimized. It has been confirmed that the sensor responds promptly to 1 ppm HF gas at room temperature, and returns to its original level once the HF gas is removed.

Interfacial phenomena in composite hollow insulator

Long term reliability has been an issue in the practical use of composite hollow insulators for many years and much basic research and numerous field tests have been conducted. However, very little research on the reliability of interfaces between the FRP core and silicone rubber housing of composite hollow insulators has been reported in comparison with extensive research on pollution proofing on the surface. Although a six- or seven-year field test on composite hollow insulators demonstrated that they satisfied practical requirements through electrical and mechanical tests, decreased interfacial adhesion strength was observed. This paper describes the results obtained from an accelerated deterioration test with samples simulating the interface between the FRP core and silicone rubber housing. They confirmed that the expected lifetime of interfacial adhesion of the composite hollow insulator exceeded 25 years. The decline in dielectric performance due to the ingress of rain or moisture into the interface was assumed to be a consequence of degraded interfacial adhesion. However, the thermal and electric simulations revealed that the resistance of the interface retained a sufficient level even with the ingress of water or moisture. Therefore, the composite hollow insulator could maintain its required dielectric strength for much more than 25 years.

Compact switching technologies, state-of-art and future trends

The development of EHV and UHV substation equipment have been proceeding to cope with the electricity demand expansion due to economic growth in the world. Simultaneously, the requirements for substation equipment compactness, cost reduction and efficiency also have been emphasized in the competitive market. This paper introduces several examples of recent developments on the compact and reliable switching technologies. They include advanced diagnostic techniques based on field data for operation and maintenance, and monitoring and diagnostic systems, controlled switching supported by information technology with the latest sensor technology and information network.