| Measuring accurately, transmitting optical-fibredly, and output digitized are the three main features of electronic transducer, and it is also the development directions of transducer. OCT is the perfect transducer for these three features, but the temperature excursion problem and the no operating stability problem have baffled its utility in power system.The Optical Current Transducer following Faraday magneto-optic effect has been totally researched and developed only by our teams. OCT has no saturation phenomenon, has good dynamic response ability and insulating property, it also can measure the non-periodic component and the various alternating current harmonic components accurately. Aiming at the temperature excursion problem that OCT faced, the Adaptive Optical Transducing Principle has been presented to solve it, and the precision of steady state measurement can be upper to 0.2s degree, so that it can completely meet the demands of the development of modern power system. This paper has researched the defending magnetic-field interference principle of OCT to solve the question of no operating stability and has also studied the digitized technique of OCT.To obtain the ability of defending magnetic-field interference, this paper has put forward Solenoid Three Phases Magnetism Orthogonal Principle and Bucking Magnetism Optical Transducing Principle, and has designed bucking magnetism optical sensing head. This kind of sensing head has simplified light path structure thoroughly, the long time operation stability has been improved greatly. This sensing head can meet the demand of the ability of defending magnetic field interference in power system, and it is conditional duality with polarized light around electrify conductor. Compared with solenoid gathering magnetism optical sensing head, the volume is smaller and the cost is lower of bucking magnetism sensing head. 25 months continuous operation in field indicates that OCT which has used this structure can operate stably in practice.IEC60044-7/8 prescribes that merging unit is the digital interface of electronic transducer and secondary equipment. In the standard of substation automation IEC 61850, 9-1 and 9-2 prescribe the transmission of bay level and process level, they all relate to the implement goal of merging unit(MU). Comparing and studying these three standards deeply, it is very important to realize and improve merging unit. This paper divides MU to three function module based on IEC61850-9-1. According to the multitask parallel characteristic of MU and OCT interface, the scheme to realize MU used FPGA is confirmed, and the idea to set up optical measurement system(OMS) is put forward.Monitor and control of power system is moving from time section to time process, and protection and control of power system is moving from spot and local to global of electric network. To avoid the severe destroy of power system accident, safety defense system of power system has been set up. Wide area measurement system (WAMS) which based on phase measurement unit (PMU) supplies the accurate dynamic process datum to electric network, and will become the base measurement system of electric network protection and control. Ferromagnetic coil current transducer can't measure dynamic process of electric network accurately, when accident comes, it saturates quickly because of non-periodic component, this induces PMU measures unsafely, the reliability of WAMS is descending. According to those characteristics of OCT, this paper has built up wide area optical measurement system (WAOMS).OCT based on Faraday magneto-optic effect conquers the shortcomings of electromagnetism current transducer and Pogowski coil current transducer, has wide dynamic measurement range and frequency response range, it can not only measure line-frequency alternating current signal, kinds of harmonic signals and non-periodic signal, but also recur transient signals of electronic network exactly, it has better dynamic response ability. This kind of OCT can get hold of the entire current of transmission lines completely, according to this characteristic, this paper put forward the entire current differential protection arithmetic of extra high voltage (EHV) base on OCT.
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