Effect of BN size on AC breakdown performances of PTFE/BN composites

To satisfy the rapid development of energy requirements, power transmission with higher voltage must be adopted. The large improvement in transmission voltage needs more excellent power equipment and better materials to meet its insulation requirement. Polytetrafluoroethylene (PTFE) nozzle used in high voltage circuit breaker faces the issue of breakdown and arc ablation, and thus superior performance nozzles are urgently needed. Previous work has proved that boron nitride (BN) is excellent filler, which can greatly improve the arc ablation performance of nozzles. Moreover, the effect of BN size on arc ablation characteristics has been studied. However, the influence of BN size on breakdown performance is still unknown. In this paper, PTFE filled with BN of different size are prepared to study the effect of BN size on AC breakdown performances of PTFE/BN composites. Scanning electron microscope (SEM) was used to characterize the dispersion condition of BN sheets in PTFE matrix. SEM results show that BN sheets are uniformly dispersed in PTFE matrix. AC breakdown results show that the breakdown strength of PTFE/BN composites increases with the increasing BN size. And the value of breakdown strength of PTFE/BN composites filled with 3 um BN is 63.24 kV/mm, which has been enhanced by 103% compared with that of unfilled PTFE (31.17 kV/mm). Thermally stimulated current (TSC) results show that the trap parameters have been greatly changed after BN is introduced into PTFE matrix. Based on the above experimental results, the relationship between breakdown strength and trap parameters is discussed. The improvement of breakdown performance is considered to be closely related to the change of trap depth and trap density, which can influence the charge transport properties in materials.