Reduction techniques of partial discharge, dissipation factor, and external corona for high voltage stator windings

High voltage stator windings in modern electric generators are subject to high electrical, mechanical, and thermal stress. Operation of these machines in both air and high pressure hydrogen results in different considerations. Operation in the air environment doesn´t offer the dielectric advantages of operating in high-pressure hydrogen. The two major design factors that are significant for the design of high voltage stator bars to be operated in air, are corona activity and PD activity. These of course are closely related. With the movement to increasing the power density of generators, which means operation at higher voltages and higher insulation stress levels, it has become more critical to be sure the design constraints are met in the stator bar design to minimize both partial discharge activity and corona activity involving the stator bars. The stator bar insulation system must be designed for minimum partial discharge activity and ideally is corona free at the stator winding operating stress levels, and at the operating conditions (temperature and pressure) the generator is subject to. This paper will present the findings associated with the development work in designing, testing and implementing a PD reduced and corona free design.