Space Charge Formation in LDPE/MgO Nano-composite Thin Film under Ultra-high DC Electric Stress

Nano-composite technology makes it possible to improve dielectric properties, such as resistivity, breakdown strength and so on, under high DC stress. However, the mechanism of the improvement in MgO nano-composite LDPE (LDPE/MgO) has not been clear, yet. We attempted to clarify the mechanism of the improvement on the electrical properties focused on the space charge formation. To investigate the influence of MgO nano-filler on space charge profiles, we measured the space charge distributions using PEA system under DC electric field of 50 to 250 kV/mm. In the case of LDPE without nano-filler, a positive packet-like charge injection with peak charge density of more than several hundred C/m³ were measured under more than 150 kV/mm. In the case of LDPE/MgO with MgO content of 0.2 phr, an oscillating behavior of packet-like charge was observed when the DC electric field of more than 200 kV/mm was applied to it. On the other hand, in the case of LDPE/MgO with MgO content of more than 0.5 phr, there is no remarkable charge injection. It is thought that space charge behavior is drastically changed by adding only more than 0.5 phr of MgO to LDPE. The nano-composite including more than 0.5 phr shows a superior property to prevent the injection of space charge into bulk