  To solve the problems of instability and thermal stress birefringence of
voltage divided medium in optical voltage sensor (OVS), a half-wave voltage
regulation method based on a central symmetry electrode and an arbitrary
directional electric field is proposed in this paper. The method uses a
center-symmetric copper foil electrode or the ITO (Indium Tin Oxide)
transparent electrode to apply voltage, which can arbitrarily adjust the
direction of the average electric field in the crystal, so as to improve the
half-wave voltage of the bismuth germanate (Bi4Ge3O12, or BGO) crystal directly
without additional SF6 gas or quartz glass. The internal electric field of the
BGO crystal is simulated by the finite element method, and the half-wave
voltage is calculated by the coupling wave theory of electro-optic effect. The
results show that the maximum regulated half-wave voltage, considering the
1{\deg} angle, can reach 2.67e3 kV. And this is consistent to the experimental
results 1.72e3 kV with difference of 35.6%. For the measurement of 110kV line
voltage, that is, 63.5kV phase voltage, to ensure a 0.2 accuracy class, the
angle error of incident light, and the polarization direction and the electric
field direction is required to be less than 3.9', which can be achieved by the
existing technologies.
