Electrical properties of polymers: space‐charge behaviour in insulating polymers under high‐voltage direct current

The space‐charge distributions in various low‐density polyethylenes (LDPEs) under a high DC voltage were measured. They strongly depended upon the physical structure of the LDPE, additives, electrode materials, applied field and temperature. Both positive and negative carriers were injected more easily from the semiconductive (SC) electrode than the Al or Au electrode and, as a result, a larger amount of space‐charge was accumulated for the SC electrode. Space‐charge dynamics depended upon the density of LDPE. Injected space‐charge moves more easily toward the counterelectrode in LDPE with a lower density and it decays more quickly after short‐circuiting. Additives, such as antioxidants and by‐products of crosslinking and oxidation of LDPE, strongly affected the space‐charge distribution in LDPE. These results give a good guide for the development of high‐voltage DC (HVDC) extruded polyethylene cables.