The Research On Differential Protection Device For Transformers Based On Double CPU

In recent years, with the accelerated pace of smart grid’s construction in China,the traditional relay protection devices have been difficult to meet the needs of the grid on intelligence and automation. We must furnish protection device of superior performance for transformers,especially in some hub substations.The device can act accurately,timely and reliably to guarantee electric power network running safely if falls. Therefore, the paper designs a differential protection device for transformers based on double CPU, which combines the analysis of the traditional differential protection device and the development of the current microcomputer protection.Firstly, this paper analyses the current development of differential protection for transformers at home and abroad. Summarizing and analyzing the technical problems that exist in the differential protection. On this basic, especially about how to differential magnetizing inrush current from internal fault current. Secondly, the advantages and disadvantages of various algorithms are discussed. On this base, Fast Fourier algorithm is used for the cored algorithm of the device. At the same time, the theory of phase space reconstruction is put forward in this paper.It proposes that using correlation dimension to identify the magnetizing inrush current and the internal fault current instead of means of second harmonic. And this paper verifies the feasibility of the theory by simulation.Thirdly, the paper adopts independent system consisting of DSP and ARM,which are responsible for the protection system and management system respectively and communicate by RS232.It takes the industry standard MODBUS protocol as data communication protocol standards CRC check can guarantee the accuracy of the data transmission.Protection board reserves the remove communication interface of RS485for real-time monitoring of substation automation.Management board has developed two sets of circuit for communication interface of Ethernet and RS485.At last,this paper also gives programs of software design.From the above-mention,the paper adopts Fast Fourier algorithm as the cored algorithm of the device,which ensure quick response and high calculation accuracy.Meanwhile,the theory of phase space reconstruction is applied in the device to identify the transformer magnetizing inrush current and the internal fault current.The two algorithms provide a strong support for theoretical analysis of collecting data.The complementary advantages of double CPU design provide hardware support for the accomplishment of differential protection device.The software uses module architecture to design,making the flowchart clear.All the designs make the performance of protection device greatly improved,which has a certain realistic significance for transformer running safelys and steadily.