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Current pulses, in the form of partial discharges, are known to be precursors of electrical breakdown in dielectric liquids.The precise measurement of these pulses is of great value for the understanding of the breakdown mechanism. The measurement of current pulses under impulse voltage is very difficult when using conventional electrical measurement systems. To overcome this difficulty, a novel measuring system using fiber optics and a light emitting diode (LED) has been developed. In this paper, the improvements in time response and charge sensitivity of such a LED current-pulse measurement system are described. Using this system and a high speed shadowgraph assembly under impulse conditions, the current pulse and the streamer initiation in dielectric liquids are measured simultaneously.

A new pimarane-type diterpenoid, sucupiol (1), and nine known furanocassane-type diterpenoids, vouacapane (2), 7-hydroxyvouacapane (3), 7-acetoxyvouacapane (4), 6-hydroxyvouacapane (5), 6-acetoxyvouacapane (6), sucutinirane F (7), sucutinirane E (8), 6, 7-diacetoxyvouacapane (9), and 6, 7-diacetoxyvouacapane-14-al (10), were isolated from the seeds of Bowdichia virgilioides and their structures were elucidated by using 2D NMR data. The isolation of 1 provides evidence to support the presence of intermediate A in the course of biosynthesis of furanocassane-type diterpenoids.

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