Computer aided design of an end corona protection system for accelerated voltage endurance testing at increased line frequency

Abstract

Due to highly nonlinear material characteristics the design of end corona protection systems (ecp-system) is a time consuming process. In order to accelerate this process a finite element model is developed. The model takes the nonlinear electrical and thermal coupled material properties into account. Furthermore it is able to calculate the electric and thermal behaviour of a painted or taped ecp-system. In this paper a special model is used to design a 500 Hz ecp-system. The paper quantifies why it is not possible to apply the ecp-system that was designed for power frequency also at a ten times higher frequency. Such a system is needed to accelerate the determination of the voltage endurance characteristics enabling the qualifying process of new or modified stator groundwall insulation of large turbine generators. In the first step the electrical and thermal behaviour of the insulation system with an existing ecp-configuration (50 Hz and rated voltage of 27 kV) is recalculated for an increased frequency of 500 Hz and 33 kV. In the next step an optimized layout is calculated with a new numerical algorithm, which is implemented in the finite element calculation and being efficient with calculation time. The newly developed design is verified by a test setup operating at 500 Hz and the electrical field strength distribution and temperature profile is measured.