Investigations of conductive particles in gas insulated Systems under DC-conditions

Gas insulated systems, have proven to be reliable for many years. But despite of a high availability some defects, in particular free moving particles can be very critical. Contamination with particles can result from mechanical abrasion or due to vibrations as well as the enclosures damages during the assembly. A further aspect is that power transmission with DC is getting more important. Therefore Gas Insulated Systems operated with DC will be required in the future. But particle behavior under DC-condition is much more different than under AC-condition. The aim of our investigations is a realistically determination of particle movement in a small scale set up with gas filled test vessel. An appropriate electrode arrangement was designed in order to achieve a similar utilization factor of a real size arrangement. To get an optimized field distribution, simulations by a FEM-program were undertaken as well as different electrode forms were used in the experiments. Experiments were carried out with different sizes of particles at different gas pressures with SF₆-gas. In order to get a correlation between particle movement and partial discharge activity, a camera was synchronized with the PD-measurement. Finally statistical evaluation of the lift-off field strength was made for both polarities.