Proposal of GF (Gas Filled) Insulation for Rotating Machines

Gap or void discharge and Creeping discharge were measured in several kinds of gases at different pressures with model specimens, such as a gap model between two parallel plates of glass, a model of single plate of glass, epoxy-mica insulation coils, and a motorette degraded by a series of functional test., From the experimental results, it is made clear that discharges in open type (ventilated) void and creeping discharges are remarkably suppressed with increasing the gas pressure, and discharges in high voltage rotating machine winding are also suppressed in compressed gas due to the transition of included voids from closed type to open type. The latter was confirmed by the measurements of a turbine generator after long service. These effects are most distinguished in SF6 gas and hydrogen gas above 1.5 atg was superior in the discharge suppression effect to the air at O atg. Moreover, the breakdown voltage of epoxy mica insulation containing many ventilated voids rises remarkably with increasing gas pressure, approaches to that of epoxy vacuum-pressure impregnated coil when SF6 gas at 6 atg is filled. Based on these data, the authors proposed the availability of GF (gas filled) insulation system in the rotating machine.