Research on cross-linked structure of poly(styrene-co-divinyl benzene) and vacuum flashover characteristics

Poly(styrene-co-divinyl benzene) bulk material is widely used in vacuum insulation system due to its excellent flashover hold-off capability. In this paper, the relationship between flashover voltages and cross-linking density was investigated. Poly(styrene-co-divinyl benzene) materials were synthesized by styrene and divinyl benzene (DVB) via free radical polymerization. Flashover voltages were measured under nanosecond pulse voltage. Cross-linking structures were characterized by Fourier transform infrared spectroscopy and Dynamic mechanical analysis. Relative permittivity (ε') and decay curves of surface potential were tested for mechanism analyzation. Results show that the cross-linking density linearly increases with the content of DVB increases from 1.0 wt.% to 3.0 wt.%, while the flashover voltages improve firstly and then reduce with the peak voltage at 53.1 kV of sample P20. The relative permittivity (ε') is found to be reduced with the increased cross-linking density, while the surface initial potential increases firstly and then decreases. Results indicate that, the decrease of ε' can promote the improvement of the flashover voltages. However, when the value of ε' decreases in a small range, the weakened capability of electrons capture caused by excessive cross-linking plays the leading role to reduce the flashover voltages.