Research On High Precision Optical Current Transducer

With the development of State Strong Smart Grid, optical current transducer based on Faraday magneto-optical effect will become an ideal transducer to service the grid. Because it has many advantages, such as high measurement accuracy, optical fiber transmission, digital output and so on. However, due to the impact of external factors such as temperature drift in practice, optical current transducer can not work in the long-term stable situation, making it having not been used in a large range. To solve the problem caused by temperature drift, the double closed-loop self-tuning method is proposed in this paper for the first time. It has theoretically demonstrated the mechanism how temperature change affect the optical current transducer based on Faraday magneto-optical effect. And the mechanism has also been verified by a large number of experiments. On this basis, a new type of optical current transducer system has been designed. That is the double closed-loop self-tuning system. This system includes two independent systems, the inner and outer loop system. For the inner loop system, a beam splitter is added to the optical source output port to separate the initial light intensity according to a certain percentage. And part of the initial light intensity is fed back to DC source control system to form the inner loop system, making the initial light intensity stable. For the outer loop system, in the original optical current transformer basic structure, the photoelectric conversion electric signals are processed by the high-precision weak signal processing method, and then separated by the high-precision AC and DC signals separation method. The DC signal affected by temperature change is extracted as outer loop component. After DC signal is compared with the basic light intensity that is set by optical source, the compared value is input into the high-stability optical source with controllable DC source and the DC source current is provided to the optical source of optical current transducer. Thus, the double closed-loop self-tuning system is formed. At the same time, DSP system is used to analyze and process signals realtimely. So it has realized dynamics negative feedback adjustment and the experimental results have reached expected targets. And the influence, caused by temperature change, is also offseted, which will further enhance the measurement accuracy and operational stability of optical current transducer.