Influence of Sample Thickness of Low-Density Polyethylene Film on Packet-like Charges Behavior and Dielectric Breakdown

Many research works have been reported on space charge accumulation characteristic in polyethylene based materials, which are used as a power cable insulating material. In these reports, some of them show the relationship between the space charge accumulation and dielectric breakdown under DC high electric field. For example, Matsui et al, showed that the packet-like charges injected into Low-Density Polyethylene (LDPE) film with thickness of ca.150 mu m lead to the dielectric breakdown under DC high electric field. The report said that the dielectric breakdown occurred within 30 minutes under various applied DC electric field of more than 200 kV/mm. Furthermore, the electric field in the material reached to about 550 kV/mm. It is considered that the dielectric breakdown in the LDPE is caused by an enhancement of the electric field locally. However, in our research, the dielectric breakdown was not observed in relatively thin LDPE film with a 30 m-thick. In this study, we measured the space charge distribution in thin LDPE film of 30 mu m-thick. The measurement was carried out using an improved PEA (Pulsed Electro-Acoustic) system with the positional resolution of less than 3 mu m. Using this improved system, we investigated the influence of sample thickness on packet-like charges behavior and dielectric breakdown. As the results, we found while the packet-like charges behavior in 30 mu m LDPE films showed a similar tendency to Matsui's results, the dielectric breakdown was not observed in the thin sample. In this report, we tried to understand the influence of the sample thickness on the dielectric breakdown.