Research On Combined Optical Voltage & Current Transformer

Compared with conventional voltage transformers and current transformers, combined optical voltage & current transformers (COVCT) have many advantages, such as simple insulation structure, immunity to electromagnetic interference, no saturation effect, no flammable materials such as oil, and light weight etc. A COVCT can measure high voltage and large current simultaneously. The emphasis of this dissertation is put onto the study of the COVCT without capacitor divider, the reflection-type transverse modulation optical voltage sensor and the orthogonal dual-total-reflection optical current sensor by summarizing and analyzing the results obtained in literature. A novel 220kV COVCT has been developed.The principle of an optical voltage sensor based on the Pockels electro-optic effect is described in detail. The basic norms of constructing an optical voltage sensor are proposed. The effect of birefringence on optical voltage sensor is analyzed, and the principle of dual-light-channel compensation is described.The reflection-type transverse modulation optical voltage sensor is analyzed in detail for the first time in this dissertation, and a novel optical voltage sensor with dual-light-channel temperature compensation is proposed. Experiments showed that the stability of the novel optical voltage sensor was improved distinctly.The reasons of affecting the stability of the optical voltage sensor are analyzed in detail by analyzing the devices, structure and electronics. The methods of improving the stability of optical voltage sensor are proposed. Some experiments about the stability of the optical voltage sensor have been done. These experiments showed that the stability of the optical voltage sensor is excellent.The principle of an optical current sensor based on the Faraday magneto-optic effect is described in detail. The mathematics model of the effect of reflection and birefringence on the optical current sensor is constructed and simulated. The reasons of affecting the stability of the optical current sensor are analyzed in detail. Some experiments about the temperature characteristics and linearity of the optical current sensor have been done. These experiments showed that the characteristics of the optical current sensor are excellent.The insulation structure of the COVCT is designed by analyzing the insulation characteristics of SF6 gas. The electric field distribution of the COVCT is calculated using the Finite Element Method (FEM). A series of tests including ratio error, stability, and insulation characteristics have been done to test the COVCT system.