Inner Electric Field Analysis And Sensor Optimal Design Of New Optical Voltage Transducer

With the voltage level rising and the capacity increasing of the power systems, traditional voltage transformer has exposed some problems, such as bulky, not easy in insulation, very small linear measurement range, no digital interface, etc. So it is unable to meet the requirements of intelligent power systems. Although optical voltage transducer (OVT) can overcome those defects, but there are still many problems unresolved, such as small measurement range, seriously affected by temperature drift and crystal’s additional birefringence. In recent years, research on how to eliminate the birefringent and compensate temperature, like the double optical path method and the double crystal method, has been widely concerned, but these methods have failed to solve the problem from the root.For OVT based on the Pockels effect, the main issue is the limitations of polarization interference measurement model. Since the electro-optic phase delay can not be directly acquired, polarization interference measurement model is always employed. It converts an electro-optic phase delay into the voltage to be measured with a light intensity modulation. Such measurement model dependent on light power detection, can only realize approximate linear measurement in a limited phase delay. And also makes the stability and reliability of OVT seriously affected by temperature drift, an additional phase delay in the crystal and half-wave voltage, thus unable to meet the requirements of power systems. So, there is an urgent need to design some kind of new OVT which can realize direct and linear measurement of the electro-optic phase delay, and solve problems such as half-wave voltage’s limit and temperature drift.This paper analyses the limitations of polarization interference measurement model and proposes a new type of OVT based on convergent polarized light interference, this new OVT can realize direct and linear measurement of the electro-optic phase delay. It converts crystal electro-optical phase to spot image’s rotation angle. This new methodology is independent on light intensity, has a wide measurement range from 0° to 180°, and its measurement range is not restricted by the crystal half-wave voltage. This paper analyses the theory of this new OVT in detail and gives the method of how to read the spot’s rotation angle. The actual measurement results are also presented which show the new sensor being capable of sensing an angle up to 320° with a good linearity.Furthermore, this paper designs the structure of such new OVT for the 110 kV power grid, though simulation of Ansoft Maxwell. The designed structure will provide a reference for the development of the prototype.The article also analyses the influence of crystal’s shape and interference electric field on the voltage measurements. And proposes a method to improve the electric field distributions of electro-optic crystal used in the transverse modulation mode by attaching some kind of media on the crystal. Through the simulation of a 110 kV OVT, the method is proved being effective in improving the distributions of electric field in crystal and reducing the measurement errors caused by an optical path offset and interference field. The improvement can improve the accuracy and stability of the OVT.