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For many years, we have been developing flexible sensors made of braided piezoelectric poly-l-lactic acid (PLLA) fibers that can be tied and untied for practical applications in society. To ensure good quality of sleep, the occurrence of bruxism has been attracting attention in recent years. Currently, there is a need for a system that can easily and accurately measure the frequency of bruxism at home. Therefore, taking advantage of the braided piezoelectric PLLA cord sensor's unique characteristic of being sewable, we aimed to provide a system that can measure the frequency of bruxism using the braided piezoelectric PLLA cord sensor simply sewn onto a bed sheet on which the subject lies down. After many tests using trial and error, the sheet sensor was completed with zigzag stitching. Twenty subjects slept overnight in a hospital room on sheets integrated with a braided piezoelectric PLLA cord. Polysomnography (PSG) was simultaneously performed on these subjects. The results showed that their bruxism could be detected with an accuracy of more than 95% compared with PSG measurements, which can only be performed in a hospital by a physician and are more burdensome for the subjects, with the subjects simply lying on the bed sheet with a braided piezoelectric PLLA cord sensor sewn into it. [ABSTRACT FROM AUTHOR]

We developed an interesting instrument in manufacturing a biodegradable polymer-insulated cable, with a variety of new functions. By using this instrument, we manufactured a poly-l-lactic acid (PLLA)-insulated cable. We measured the basic electrical insulation characteristic of the PLLA-insulated cable, and the following results were obtained. The mean breakdown strength of the PLLA-insulated electric wire was approximately 3.5-fold that of a polyvinyl chloride insulated and polyvinyl chloride sheathed flat-type cable (VVF cable). In addition, a bending test of the PLLA-insulated electric cable was performed. We obtained good results. Index Terms--Biodegradable polymer, cable, electrical breakdown, polylactic acid.

We measured the basic electrical insulation characteristic of biodegradable polylactic acid (PLA), and the following results were obtained. The volume resistivity, dielectric constant, and dielectric loss tangent measured at room temperature were almost the same as those of crosslinked polyethylene (XLPE) currently used as insulating material for cables and electric wires. The mean impulse breakdown strength of PLA was about 1.3 times that of XLPE. Also, space charge accumulation in PLA and XLPE was measured. The amount of space charge accumulation in PLA was one-half that in XLPE when dc voltage was applied for a short time. Index Terms--Biodegradable polymer, electrical insulation characteristics, film, polylactic acid (PLA).

This paper describes the results of a long-term reliability test of a newly developed 500 kV DC oil-filled cable and accessories that transmit up to 2800MW. This is the largest capacity ever used for submarine cables. The test line was 500m and consist of submarine cables, land cables, and several kinds of accessories. An optical fiber sensor was first installed in the oil duct of the cable to measure the conductor temperature directly under application of DC voltage. From 1994 to 1996, we carried out an accelerated electrical and thermal aging test equivalent to 40 years, a load cycle test, a polarity reversal test and a transient overloading current test. Satisfactory breakdown strength was confirmed in the residual test which followed the long-term test. These results have been instrumental to the decision to construct 500 kV DC commercial submarine cable lines. Keywords: DC power transmission, Underwater cable, Power cable testing, Oil filled cable, Aging

Discusses the result of a long-term reliability test of a 500 kilovolt direct-current (DC) oil-filled cable and accessories that transmit up to 2800 megawatts. Largest capacity ever used for submarine cables; DC power transmission; Satisfactory breakdown strength; Accelerated electrical and thermal aging test; Load cycle and polarity reversal tests.

For many years, we have been developing flexible sensors made of braided piezoelectric poly-l-lactic acid (PLLA) fibers that can be tied and untied for practical applications in society. To ensure good quality of sleep, the occurrence of bruxism has been attracting attention in recent years. Currently, there is a need for a system that can easily and accurately measure the frequency of bruxism at home. Therefore, taking advantage of the braided piezoelectric PLLA cord sensor's unique characteristic of being sewable, we aimed to provide a system that can measure the frequency of bruxism using the braided piezoelectric PLLA cord sensor simply sewn onto a bed sheet on which the subject lies down. After many tests using trial and error, the sheet sensor was completed with zigzag stitching. Twenty subjects slept overnight in a hospital room on sheets integrated with a braided piezoelectric PLLA cord. Polysomnography (PSG) was simultaneously performed on these subjects. The results showed that their bruxism could be detected with an accuracy of more than 95% compared with PSG measurements, which can only be performed in a hospital by a physician and are more burdensome for the subjects, with the subjects simply lying on the bed sheet with a braided piezoelectric PLLA cord sensor sewn into it.