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40. Effects of crosslinking byproducts on space charge formation in crosslinked polyethylene

Author

Maeno, Yasumasa, Hirai, Naoshi, Ohki, Yoshimichi, Tanaka, Toshikatsu, Okashita, Minoru, and Maeno, Takashi

Subjects
Dielectrics -- Research, Cables -- Research, Business, Electronics, Electronics and electrical industries
Abstract

Space charge is formed in cables insulated with crosslinked polyethylene. It has not been clear whether the crosslinking byproducts or the crosslinked polymer morphology is responsible for the space charge formation. In order to clarify this point additive-free non-crosslinked low-density polyethylene, additive-free crosslinked polyethylene, and degassed crosslinked polyethylene were soaked in the crosslinking byproducts and the space charge distribution was measured after dc voltage application. Samples tested are divided into two categories. The first category is a soaked single-layered sheet and the second category is a two-layered specimen consisting of a soaked sheet and a non-soaked sheet. As a result, the following conclusions were obtained. (1) Cumyl alcohol is responsible for homo-charge layers in front of the electrodes in both low-density and crosslinked polyethylene sheets. (2) Acetophenone is responsible for hetero-charge formation in crosslinked polyethylene, presumably as a synergistic effect with water. (3) [alpha]-methylstyrene has no effect on space charge formation in low-density polyethylene, while it assists charge trapping in crosslinked polyethylene. (4) Charge trapping occurs easier in degassed crosslinked polyethylene than in low-density polyethylene, probably because of carbonyl groups induced by crosslinking. Index Terms--Charge trap, Crosslinked polyethylene, Crosslinking byproducts, Power cable, Space charge.

Published
2005

41. Chemical group in crosslinking byproducts responsible for charge trapping in polyethylene

Author

Hirai, Naoshi, Minami, Ryotaro, Tanaka, Toshikatsu, Ohki, Yoshimichi, Okashita, Minoru, and Maeno, Takashi

Subjects
Electrical cables -- Usage, Electric charge and distribution, Polyethylene -- Usage, Crosslinked polymers -- Usage, Trapping -- Usage, Business, Electronics, Electronics and electrical industries
Abstract

It is known that space charge is formed in cables insulated with crosslinked polyethylene. It is probable that the crosslinking byproduct or the crosslinked polymer morphology is responsible for the space charge. In order to examine the former possibility, an additive-free low-density polyethylene sheet was soaked in various liquid chemicals including the crosslinking byproducts and space charge distribution inside the sheet was measured under dc voltage application. As a result, space charge appears in the vicinity of the injecting electrode only in the case that the sheet was soaked in the liquids with at least one hydroxyl group in their structures. Therefore, it is concluded that cumyl alcohol, which is the only byproduct with a hydroxyl group in its structure, is responsible for the formation of space charge in polyethylene on the assumptions that chemical functions of a given molecule act separately from each other and that other contributions such as the crosslinked polymer morphology are negligible. Index Terms--Power Cable, Polyethylene, Space Charge, Electrical Insulation, Charge Trapping.

Published
2003

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