The Research Study And Design Of High Voltage Distribution Network Grounding Fault On-line Detection System

The operation of the small current grounding protection system can significantly improve the safety of power supply,thus is widely used in power distribution network in China.In distribution network operation,in the event of the small current grounding,generally easy to be found.Because small current are faint and difficult to detect,and fault occurring just line from the initial stage of the operation effect is not obvious.If run not to screen for a long time will cause more problems,such as line tripping and equipment destroyed,great impact on the use of the user.So the failure should be detected in a timely manner,inform the staff and find out the location of the fault line.There are many factors that can influence of fault line selection,but hasn't been very good to solve these problems.The above mentioned problems,many researchers have been carrying on the research a lot of line selection methods have been proposed one after another,all have their own advantages and disadvantages of each line selection method.Because of the existing fault line selection method is a lot of more phyletic,the paper also has carried on the summary and induction.Each line selection method has its own advantages,have some shortcomings.To select the best method is to first half wave method,but because of the high voltage line grounding fault of half wave signal is small relative to the high voltage amplitude,interfere with the big difficult to detect,it is not suitable for practical application.Through comprehensive comparison,this paper chose the method of harmonic component,using the Fourier change data for calculating and analyzing the data,set up a model of the small current grounding system,through the oscilloscope to observe the change of the zero sequence current waveform,single-phase earth fault in neutral point grounding system simulation was carried out.Through the analysis,the paper to fundamental wave and harmonic characteristic parameters for fault from 1 to 64 times,through calculating the harmonic amplitude,the two zero sequence currents obtained base harmonic of fault line selection criterion.Based on the STM32 series single chip microcomputer as the core has completed the small current grounding fault line selection of hardware system and software system design.Software system mainly includes the zero sequence current data sampling module,harmonic calculation module,fault diagnosis module,display alarm module,tripping module,data storage module.In the hardware system based on STM32 microcontroller built-in A/D converter as the core of analog input circuit,STM32 minimal system and fault alarm circuit and so on.Practical application results show that this line selection system,the protection device to select accurately capture the fault line,achieve the function of the small current grounding fault line selection.