Potential distribution on the stress grading system of high-voltage rotating machines –I measuring system

A surface potential measuring system has been developed utilizing a Pockels sensor to measure the potential distribution of the stress grading (SG) system of form wound motor coils. A Pockels BGO crystal is positioned just above (<1 mm) the SG, and the capacitively-induced voltage on the surface of the BGO crystal adjacent to the SG is measured by using Pockels effect of the BGO crystal. The sensing system is applicable to surface potential measurement over wide frequency region from 0.001 Hz to 100 MHz. The spatial resolution of the measuring system after enhancement through deconvolution is discussed with the result that the -3 dB spatial frequency of the measuring system is 0.22 cycle/mm which implies a resolution in the range of 4 mm.