Toshimitsu Yamada

Development of potential grading layer for high voltage rotating machine

A new potential grading layer used for a high voltage rotating machine has been developed based on the percolation behavior of composite made with a resin, triiron tetra oxide (Fe/sub 3/O/sub 4/) and/or silicon carbide (SiC). The potential grading layer was designed by using a combination of high and low resistive tapes made with a binder resin, SiC and Fe/sub 3/O/sub 4/ and showed a stable and excellent partial discharge suppression capability.

Considerations on aging tests of the class H post impregnated insulation system for rotating machines

We carried out aging tests to develop the new class H insulation system manufactured by post impregnation process for high voltage rotating machines. The following aging tests were discussed: 1) Evolved Gas Analysis of insulating materials, 2) Voltage Endurance Tests at room temperature and at elevated temperature, 3) Bending Fatigue Tests for insulated bars, 4) Motorette Tests in accordance with IEEE.Std.275, 5) Thermal Cycle Test under class H conditions.

Improvement in Oxidation and Thermal Shock Resistance of Molten Glass-Coated Carbon Materials by Interfacial Control

The coating of molten silicate glass on a porous carbon substrate was developed, without the formation of cristobalite at the carbon-glass layer interface, in order to improve the steam oxidation and thermal shock resistance. Initially, suitable conditions for coating were assumed from thermodynamic analysis. Based on these calculations, the wettability of the carbon to molten glass was modified by infiltration and pyrolysis of a Si-N precursor, and the coating with glass was carried out under higher N2 partial pressures. As a result, carbon substrates were completely sealed with glass, without the production of cristobalite at the interface, and the glass was infiltrated into the substrate. In contrast, coating with glass at lower N2 partial pressures, such as in Ar, were followed by the formation of cristobalite along with many pores at the interface. The structural changes occurring as a result of variation of the N2 partial pressure during sealing with glass are in good agreement with the thermodynamic analysis. The glass-coated carbon materials, which were fabricated at higher N2 partial pressure, possessed excellent steam oxidation resistance and thermal shock resistance.