Software Design Of Feeder Protection For Digital Traction Substation

With the IEC61850 standard drafted,promoted,the development of IEDs, especially the appearance of electrical and mechanical integration equipments, substations is about to enter a new stage of digital. Currently, a number of digital substations has been put into operation in our country.but the digital substation and the related technologies have not been applicated in our country traction power supply system.so the research on the protection equipments of digital traction substation is of great significance.Based on analysis of IEC61850 standard technical features, the IEC61850-9-2 standard,GOOSE Message transmission and the Network Solutions in Process level have been analyzed in the paper. The influence of the IEC61850 standard, non-conventional transformers and other digital substation key technology that may bring to software and hardware of the protection has been studied,and the hardware platform of feeder protection device has been discussed, then the configuration of the feeder protection and it's basic principle have been researched. Base on this, the feeder protection information model based on IEC61850 standard has been established.Because the sampling rates are not equal between the MU sampling rate and the sampling rate of of protection devices used in our country now, and the sample frame may be lost in transmission, the interpolation error of the linear Lagrange interpolation algorithm and the Parabola Lagrange interpolation algorithm has been analyzed. And interpolation error of different MU sampling rates is simulated and analysied. For the sample that may be abnormal, a method by amplitude comparison has been analyzed.And other measures in software design to eliminate the influence of abnormal datas have been summarized.Based on the specific functional module divided in feeder protection, the specific features of each functional module, the relationship and data exchange among functional modules have been designed. The software of feeder protection is devided into samples processing task, protection task and communication processing task. Then all functional module of the software have been designed in detail, the main function of protection is realized in the Windows operating system.Finally,the software test platform by PWF-3 optical digital relay tester has been built. The measurement function and protection function of the software have been tested under the normal circumstances, fault condition and the operation condition when put in No-load transformer. The test results show that the division of functions and tasks of the software is reasonable, the accuracy of the algorithm can satisfy the requirements, the logical judgement of the protection software is correct and reliable.