Carbon-based semi-conductive materials (corona armor tape or CAT), and SiC-based nonlinear grading materials have been used widely to reduce the electric field in the region where the stator bar exits from the slot in form-wound rotating machines. Recent studies show that electric field and local heating in the end-turn stress grading system become severe under PWM waveforms and high frequency repetitive pulses. In this paper, methods for accurate measurement of CAT conductivity as well as selecting the appropriate conductivity to control both the electric field and local heating were investigated, based on transient nonlinear FEM computation. The methods proposed in this paper should be adequate to optimize end-turn stress grading system of the rotating machines.