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Investigations on the basic electrical properties of Polyurethane foam material

The Polyurethane (PU) foam materials have increasingly been used as a new kind of solid insulation material, which are always inserted into post hollow composite insulators as their inner insulation section. PU foam with PU as a base material which is homogenously filled with pores, PU foam material is a possible substitute material of the air, SF6 and N2. In order to achieve a better electrical performance, the electrical properties of PU foam should firstly been studied and understood in depth. In this paper, the electrical strength, volume resistivity, permittivity and partial discharge property of PU foam have been investigated. It is the porous structure characteristic with low density that distinguishes itself from other dielectric materials. Because of the pores distributed in the PU material, the partial discharge (PD) characteristics have been put more emphasis. Four kinds of PU foam materials with different pore size and pore geometry and one kind of PU elastomer have been used in our research. The micro-pore structure of PU foam was characterized by scanning electron microscopy (SEM) method. For PD property, we mainly focus on the PD inception voltage, PD extinction voltage, discharge magnitude with applied voltage as well as its relationship with physical structure of pores. Experimental results indicated that the electrical properties of PU materials have a closely relationship with pore structure, especially for the electrical strength and PD characteristics. The electrical properties with stress on the PD behavior of PU foam were discussed in depth by combing the electrical test result and the physical property of PU foam.