Surface potential measurement of model stator bar with stress grading system by field sensor

This paper proposes a novel method for measuring the potential distribution along the stress grading system of a model stator bar whose voltage is over several tens kV. The technique uses a Pockels field vector sensor by introducing an inverse calculation process from the measured field profile to the potential profile on the measured stator bar. With this system, a potential distribution along a model bar under 50 kV_p, 50 Hz voltage is successfully measured. In principle, it is possible to estimate the potential either by measuring the horizontal or vertical component of the field. The utilization of the vertical component is preferable in measuring a model bar due to robustness against optical alignment errors. Through the potential distribution measurement of the model bar, although the maximum value of the electric field increases slightly with the applied voltage, it is confirmed that the electric field grading function was working due to the non-linear resistive material.