Space charge characterization in aged LDPE amalgamated insulation regions from underwater telecommunication systems

The requirement of insertion of optical amplifier units and joints, into long-distance submarine telecommunication systems, results in regions of the polymeric insulation which have to be reinstated, using injection molding techniques. These techniques introduce internal amalgamated interfaces, which subsequently can be the sites of possible electrical insulation failure in the system. Studies [1-3] have proposed that the increased risk of failure is associated with the development of stress enhancing space charge at these interfaces. This paper reports on space charge measurements, (using the pulsed electroacoustic (PEA) technique [4]), from microtomed thin film samples taken from the interface region of typical system joints which have undergone accelerated aging tests under a de voltage at room temperature. The space charge distributions obtained for the samples are discussed with reference to the underlying mechanisms of both the bulk low density polyethylene (LDPE) and the surface (LDPE /electrode interface). The effect of varying the electrode material (i.e. Au and Al) is discussed with reference to previously published data. Finally the effects of long term aging on space charge accumulation within LDFE are considered briefly.