Partial discharge detection technique using electro-optic effect

In this work, a possible new PD detection technique, based on the electro-optic effect (Pockels effect), has been proposed. Generally, commercialized nonlinear electro-optic (EO) crystals have some defects and hysteretic characteristics of which the loop is shifted downward ascribed to the microscopic change of polarization ΔP in these defects. The refractive index ellipsoid of EO crystal, such as LiNbO₃, is changed by both the externally applied electric field and its hysteresis loop of which the effect gives rise to a discrepancy of index variation. Therefore, considering the influence of hysteretic characteristics an equation is newly proposed in connecting with the phase variation of modulated laser beam through LiNbO₃ crystal under applied electric field. For this purpose, PD generated from needle-plane electrode in air has been detected by use of LiNbO₃ cell and our proposed equation is experimentally approved. As a result, it is observed that PD measurable phase intervals are limited by the crystal characteristics such as asymmetrical P-E hysteresis and half-wave voltage. The number of PD pulse occurrence and its magnitude were observed to be increased with applied voltage, which may imply that it is possible to detect PD by this newly proposed electro-optic method