This paper describes the construction of an optical voltage transformer for measuring A.C and D.C hihg potential based on the electro optical Pockels effect. Sensor element, we tested two types of photorefractive crystal, crystal Bi12SiO20 (BSO) and crystal Bi4Ge3O20 (BGO), for each obtained characterization curves, which were obtained by changing the potential level of the crystal and measuring the amount of light coming from this. It also briefly describes the opto mechanical design that makes it possible to unite in a single light source system with different optical components to pre – treatment of light before and after passing through the sensor element.