Research On Two-branch-current Optical Current Sensing Technology

With the construction of smart grid, as the key part of intelligent substation equipment, electronic current transformer becomes the mainstream of the future development trend. Optical current transformer(OCT) is a kind of electronic current transformer which has many advantages. It relies on Faraday effect to measure current, and transfers signal by fiber. So it has good insulation performance, relatively small size, wider dynamic range and digital output. OCT is the development direction of the future.But now, OCT still exist many problems, mainly concentrated in the measurement precision, anti-interference ability and long-term stability.This paper proposes a new OCT structure, two-branch-current structure, provides a new idea to solve problems upon.Firstly, this paper analyzes the merit and demerit of the bulk glass optical current transformer, and presents a new OCT structure which called two-branch-current optical current sensing unit. Established the two-branch-current optical current sensing unit’s mathematical model, gave its current measurement method.Secondly, according to the structure of two-branch-current optical current sensing unit, obtain parameters optimization scheme. Given the size of the diversion frame and the position of the sensors. Proposed methods to weaken the linear birefringence effect and external magnetic field interference effect in order to improve the measurement precision of the method.Finally, using the physical simulation experiment to verify the validity of the mathematical model. Perform magnitude measurement precision experiments under no-external magnetic interference and external magnetic interference. The experimental results show that two-branch-current optical current sensor unit reach a 0.2 magnitude measurement precision, validated sensing structure has a good ability to resist the external magnetic field interference.