Research And Design Of Micro-computerized Differential Protection Measurement And Control Device For Transformer

Power transformer is a key equipment in the whole power system, along with thecontinuous production of power transformer and the scale enlargement of power grid,transformer protection technology is still an urgent problem to be researched anddeveloped. With the rapid development of electronic technology and computertechnology, the traditional measurement and control device for transformerdifferential protection is gradually being replaced by microcomputer type devices,therefore, many related researches and applications of micro-computerizeddifferential protection measurement and control device for transformer is also rapidlyemerging, at home and abroad.In the background of the research and development of microcomputer protectionand in the basis of analysis of the characteristics and requirements of microcomputerprotection for transformer, a micro-computerized differential protection measurementand control device for transformer, which integrates protection, measurement, control,communications and other functions together, is researched and designed in this paper.The floating-point DSP chip TMS320F28335with high performance is chose ascontrol core in this device, the programmable logic device CPLD is used to simplifythe design of peripheral interface circuit of CPU and to share such function asfrequency measuring, the allocation of CAN interface and RS485series interface is tomeet the networking demand in the substation automation system.Firstly, through theresearch on the principle and characteristics of transformer differential protection, thesecond harmonic principle is used as a method to discriminate inrush current in thesystem; Secondly, by the analysis of measurement and protection algorithm, the basicelectrical parameters computing method and full-wave Fourier calculation method ispresented in this paper, and in the concrete, the effective FFT is adopted to accomplish the harmonic calculation; Finally, it is the flexible modular softwaredesigning that realized such functions as the basic electrical parameters calculation,the instantaneous overcurrent differential protection, the percentage differentialprotection for the second harmonic restraint and other logic judgments.The results prove that the micro-computerized differential protectionmeasurement and control device for transformer designed in this paper can not onlyaccurately measure the electrical parameters such as voltage, current, frequency andso on, but also it can realize the following functions: the transformer instantaneousovercurrent differential protection, the percentage differential protection for thesecond harmonic restraint and the fault alarming and interlocking function forcomputed tomography (CT) disconnection. Experimental data show that the devicecan measure parameters accurately and has rapid and reliable protection operation, itmatches the desired design requirements very well.