Analysis And Application Of Transformer Logic Protection Device Based On ARM

When a fault occurs in the power system and endangers the safe operation of the power system,it is necessary to analyze the fault type through the relay protection device,select the best treatment method and quickly deal with the fault,so as to restore the stability of the power system and achieve the optimal benefit.Because of the complexity and diversity of electrical faults,the logic of relay protection in power system is complex and the amount of data is large.The microcomputer relay protection device has the advantages of high efficiency,flexibility and reliability,small volume,low power consumption,simple maintenance and debugging,universal hardware,convenient function expansion and so on,it occupies the leading position of relay protection device.In the power system,the transformer takes the role of voltage and current conversion,in order to achieve the purpose of reasonable power transmission,it is an important equipment in the power system.When the auxiliary transformer of thermal power plant has electrical fault,if the relay protection device of transformer misoperates or refuses to operate,the power equipment will be damaged.For example,when the transformer load is heavy,the load current exceeds the protection current threshold value,causing unnecessary over-current protection maloperation.When two-phase short-circuit fault occurs in the transformer,the amplitude of over-current caused by external fault is similar,which often can not be distinguished,resulting in transformer internal protection misoperation.The south is rainy and lightning weather,often lightning will produce over-voltage phenomenon,if the lack of over-voltage identification,will cause damage to the insulation of the transformer.The processor is the core part of the hardware of the microcomputer relay protection device.It is just like the brain of the whole device.The sampling algorithm and protection logic are the main contents of the brain.In order to solve the problems encountered in the practical work of these relay protection devices,we first analyze the processor of microcomputer relay protection devices.Through a brief comparison of Cortex-M series processors,this paper puts forward the reasons for choosing Cortex-M3 processor for analysis.By analyzing the system clock unit,DMA controller,memory unit,architecture bus and peripheral module,we can understand the overall architecture design of arm Cortex-M3 processor,so as to better understand how the "brain" of the protection device is composed.Then let’s see how the protective device "brain" thinks.By comparing and analyzing the basic AC sampling algorithm and Fourier transform,the advantages and disadvantages of each sampling algorithm are shown,and then the Fourier transform related to the actual power plant is emphasized.When the transformer has different faults,after sampling the time domain signal of fault voltage and current,using Fourier transform,the frequency domain signal of electrical quantity will be obtained,and these electrical quantity data will be used for logical judgment,so as to calculate the operation state of a certain link of the system,identify the fault type,and make the corresponding export action according to the calculation results,so that the transformer can avoid damage caused by failure.Taking Nanning Power Plant as an example,this paper analyzes the actual faults,reasonably combines the protection logic of transformer longitudinal differential protection,over-current protection and zero sequence protection,and reasonably optimizes the protection setting,so as to make the protection device more suitable for the field equipment and the actual working environment.Finally,the analog circuit model is built,and the sampled electrical signal and protection logic algorithm are written into the processor.Through the test,the accuracy of the sampling algorithm and the feasibility and correctness of the protection logic are verified.The content of transformer microcomputer relay protection is combined with the actual work,and the problems encountered in the actual work are solved,from which a deeper understanding is obtained.