Study Of Optical Transformer Merging Unit In Digital Substation

Digital substation which is based on the using of non-tranditional transducers like optical transducer,establishment of IEC 61850 standard, and the rapid develepment of network communication technique,is the future of the substation automation system.Optical transducer and it's Merging Unit are the important devices to implement the digital substation.Power supply is one of the essential parts in the active photoelectric transducer. Floating type DC power supply which is used commenly nowadays has many shortages. So a new method to supply the energy to the optic-electric transform device set on high voltage side of active photoelectric transducer, by means of laser has been introduced here.The MU(Merging Unit) is the bridge from high-speed data sampling system to measurement and control device in bay level.The definition of MU and its international standards-IEC 60044 7/8 standard and IEC 61850 standard are introduced,and the main functions of MU and its implementation are researched.It divides MU into three different functional modules which are analyzed in detal. That is, receiving station-wide unitive synchronous signal and providing synchronous signal for A/D transformer; collecting the multi-channels data stream from electronic transformer,and then processing and coding the data after packing total frame based on the IEC 61850 standard; transmitting these data to bay level using fiber ethernet.A scheme using CPLD XC95288CL and motorola Coldfire MCF5272 processor is proposed.XC95288CL have the advantages of high running speed and many I/O ports ,combining the inside program coded by very high speed integrated circuit hardware description language(VHDL),so it's used to realise the function of synchronization, CRC check , serial to parallel transformation and sorting of multiple datas from electronic transducers.Coldfire MCF5272 processor and its embedded MCU(Media Control Unit)realise the packing , processing,coding and transmitting of the data.To achive the compatibility and interoperability among MU and other intelligent elctronic devices(IED) in digital substation, the MU must be modeled on the basis of object-orientede methed in the standard of IEC 61850.Here,firstly the basic features of standard IEC 61850 and the general approach to realize this standard are presented;on the basis of researching the intension of IEC 61850 information model and starting with the function analysis of MU,the attribute of MU information model and abstract communication service interface are researched,and the method to construct information model of MU is expounded.Then,the communication mapping method for abstract function service of MU and the frame format are analyzed.Finally,the basic format of the configuration file for the self-description of devices by SCL is birefly introduced.