Toshikatsu Tanaka

Characteristics of space charge formed in a laminated LDPE/EVA dielectric under DC stress

A laser-induced pressure pulse (LIPP) method was used for measuring the space charge distribution of LDPE/EVA laminate dielectrics under DC stress. A constant voltage up to /spl plusmn/20 kV was applied to a side of laminates of 0.5 mm thickness for 30 minutes. The other side is grounded. When the amount of space charge was measured by LIPP, both sides were virtually grounded. Space charge built up in or near the interface between LDPE and EVA was mainly investigated. Positive and negative voltage was applied to the side of LDPE in the laminates. It was clarified that the space charge was larger in case of LDPE negatively biased than in case of LDPE positively biased. The density of the space charge ranged around 1 nC/mm/sup 3/. The formation of interfacial space charge is analyzed.

Formation and annihilation characteristics of space charge in PE/EVA interfaces

Interfacial space charge was measured for laminated dielectrics by the laser-induced pressure pulse (LIPP) method. Specimens used for experiments consisted of low-density polyethylene (LDPE) and ethylene vinyl acetate (EVA) of thickness 0.25 mm each and were subjected to d.c. voltages up to 10 kV. The voltage was continuously applied until the space charge in the interface increased nearly to the saturation of the charge accumulation. It was clarified that the space charge formed at the interface between the two dielectrics was around 10 to 100 /spl mu/C/m/sup 2/, which was smaller than the induced electrode charge, and was long-lived after the cessation of voltage with more than two kinds of decay times. The process for formation and annihilation of interfacial space charge is presented.

Laser-induced pressure pulse measurements of space charge in PE/EVA laminates

The LIPP method was used for measuring the charge distribution at the interface between PE/EVA laminate dielectrics under dc stress. High power laser light of 300 mJ/pulse was applied to a specially coated surface of the specimen. A short (300 ps) and a long (5 ns) laser pulse were used for thin and thick specimens, respectively. The result of the measurement shows that space charge was accumulated at the interface, When it was positive, the space charge stayed at the interface on the EVA side and was not transferred to the interface on the LDPE side. On the contrary, when it was negative, the space charge was transferred to the interface on the LDPE side.

Basic study on discharge induction by laser‐produced plasmas in atmospheric air

To clarify the characteristics of the discharge induction against the delay time of impulse application with a long gap/1/, the electron and neutral particle density in the plasma were measured. The electron density was about 1023 m−3 at 10 μs after firing the laser and then gradually decreases in several tens of microseconds. The rarefied air region of lower neutral particle density takes a spherical shell profile in later stages after firing the laser. From the experiments of the laser‐induced discharge, it seems that the discharge induction was greatly influenced by the electron attachment to oxygen molecules and rarefied region of the neutral particle density.