The use of stress-grading systems proved to be essential to suppress corona in the end-turn zone of high voltage machines. Moreover, power dissipation in the end-turn region is believed to be a major factor in the deterioration process of surface field grading systems. This paper introduces two novel techniques for the design and analysis of both linear and nonlinear corona-suppression systems of high voltage machines. The first technique is based on the design of linear stress-grading systems through power-loss minimization and equalization of electric field along the end-turn zone. The second technique is based on the simulation, modeling and analysis of nonlinear stress-grading systems in the time domain using the describing function method. This model generates the time variation of the resistances as well as the surface electric field and potential and ultimately converges to the optimal design parameters of the stress-grading system.

This paper introduces a new approach for the design and analysis of nonlinear stress-grading systems for high voltage rotating machines. The method is based on the simulation and modeling of stress-grading systems using a nonlinear lumped circuit model. The nonlinear model is analyzed in the time domain using the describing function method. The model generates the time variation of the resistances as well as the surface electric field and potential and ultimately converges to the optimal design parameters of the stress-grading system. The model is iterative and adaptive where a deviation from the nominal uniform field and the upper and lower bounds on the resistance values as well as bounds on the nonlinearity factor can be set to generate optimal design parameters of the stress-grading system.

Stress-grading systems are essential for the suppression of corona in the end-turn zone of high voltage rotating machines. Unfortunately, design of stress-grading systems in industry is almost entirely based on experimental trial-and error techniques. This paper introduces a novel graphical user interface (GUI) model for the selection and design of stress-grading systems of high voltage rotating machines. The GUI model is based on two major design approaches for stress-grading systems: i: minimization of power-loss and, ii: time-domain analysis of nonlinear stress-grading systems using the describing function method. Comprehensive codes written in both FORTRAN and MATLAB® were developed for the purpose of design and analysis of linear and nonlinear stress-grading systems of high voltage rotating machines. A GUI was developed to enable the design engineer to select analyze and optimize stress-grading systems. This graphical front-end to FORTRAN and MATLAB® codes utilizes built-in functionality of MATLAB® to create graphical interface objects, interface with compiled FORTRAN functions, and generate design and analysis reports based on the data gathered from the source codes.