Space charge dynamics in LDPE

Now a days HVDC cables with polymeric insulation such as LDPE (Low Density Polyethylene), XLPE (Cross Linked Polyethylene) are widely used as compared to conventional oil impregnated HVDC cables. The polymeric insulation, despite its numerous advantages, suffers from the space charge effects whenever it is subjected to high DC voltage. It is believed that space charge causes pre-mature breakdown of cable insulation. Therefore measurement of space charge in cable insulation is considered very important in view of it´s use in HVDC transmission. The Pulsed Electroacoustic (PEA) method is generally used in the measurement of space charge in polymeric insulation. All the experiments were performed using PEA system developed in authors´ lab. In the present work authors have investigated the effect of history of voltage application on the formation of space charge in the LDPE (Low Density Polyethylene). The experiments were performed repeatedly on various film samples (100μm) taken from same lot, charge profile for all samples were similar.