Correlation Between Electroluminescence and Partial Discharges in Silicone Rubber Used for High Voltage AC Subsea Connectors

Abstract

Processing of oil and gas has been performed on topside installations close to the wells. In the future, wells will be further away from the infrastructure and more processing will be performed on the seabed. This will require more electrical power on subsea installations in deep waters and far away from the platforms and shore.

Large power cables are connected in subsea connectors at the subsea installations. Because of its good electrical abilities, flexibility and water repelling, silicone rubber is a good candidate as insulation material in these subsea connectors. As the industry looks towards deeper sea-levels and more challenging terrain, studies and research must be conducted on the materials to be used in order to estimate operation-time. Life time of the power system is crucial for the complete subsea processing plant and long term properties of the insulation materials must be known.

This study aims to find a correlation between partial discharges and electroluminescence in a pre-made cavity in silicone rubber. In total six samples have been tested; three samples with a pre-made crack in the surface wall of a cavity and three samples with a smooth surface wall in the cavity. A molding procedure in addition to a test-procedure of the samples has been found.

It has been found a clear correlation between partial discharges and electroluminescence in a pre-made cavity. If the dissipated energy is high, the emitted light is accordingly high, independent of the peak magnitude of a partial discharge. Partial discharges occur for voltages below 1 kV for all samples. Electrical tree growth was observed to occur at a lower voltage level in samples with a pre-made crack in the surface wall of the cavity. No electrical tree growth was seen in the three samples with a smooth cavity surface wall. All samples showed sign of degradation in the tip of the surface cavity.