Space charge formation and impulse tree in ethylene based polymers

摘要

1. Impulse tree initiation voltage Vt decreases with comonomer contents Cc.rn2. Vt of negative polarity is higher than positive one. But the decrease in Vt with Cc is larger in negative polarity than in positive, especially in small Cc region.rn3. impulse voltage with longer rise time gives higher Vt in negative polarity, especially in small Cc region, but not in positive polarity.rn4. In negative polarity, length of short circuit tree Ls clearly decreases with Cc , while in positive polarity Ls is almost constant.rn5. Increase in Cc increases the density of negative space charge but restricts the region, resulting in emphasis of field strength at the periphery. This model well explains the experimental results for negative polarity.