Fast space charge packet characteristics within low-density polyethylene affected by epitaxial crystallization

Abstract

The formation of space charge packet increases the maximum electric field within HVDC polymeric cable insulation. However, the influence of epitaxial crystallization on transient characteristics of space charge packet behavior in polyethylene (LDPE) under high temperature is still unrevealed. Therefore, polytetrafluoroethylene (PTFE), isotactic polypropylene (iPP), and glass (G) were adopted as the substrates to prepare LDPE samples with different epitaxial crystallization, denoted as PE-PTFE, PE-iPP, and PE-G respectively, for the measurement of space charge packet at 60 °C under −125 kV/mm. The experimental results show that space charge packets with both positive and negative polarity occurred immediately in LDPE samples after polarization, whose mobility and rising rate of electric field are at least 10 times higher than that at normal temperature. The injection amount of positive space charge packet arranged as PE-PTFE > PE-G > PE-iPP. According to the epitaxial crystallization characteristics of parallel (PE-PTFE), crossed (PE-iPP), and random (PE-G) arrangement of molecular chain, as well as the feature that hole migration is tend to be affected by molecular chain arrangement, the epitaxial crystallization of PE-iPP is contributed to the transport within inter-molecules, resulting in the difficulty of the appearance of positive space charge packet. The obtained results in this paper are important to have deep understanding for space charge behavior within cable insulation.

Keywords

• Low density polyethylene
• Epitaxial crystallization
• Fast space charge packet
• Temperature field
• Transient characteristic