Research And Development Of Fault Line Selection Device For Small Current Grounding System Based On ADSP

Small current grounding mode is a commonly used neutral point grounding mode in medium and low voltage power distribution network in China.It has the advantages of high reliability and certain protection for electrical equipment and personal safety,etc.But single-phase grounding fault occurs frequently in medium and low voltage distribution network,followed with the issue of fault line selection.To solve this problem,the aim of this article is to develop a device that has high accuracy and better performance on fault line selection.Firstly,the embedded algorithm and the hardware structure of several common kinds of line selection device were summarized.This paper analyzed the steady state and transient characteristics of the lines’ current after the breakdown occurred,which proved the feasibility of fault line selection algorithm based on Prony fitting method and the transient feature of zero sequence component.The transient feature is informative but non-persistent because its high-frequency part attenuated rapidly.The parameters of the high-frequency part can be extracted conveniently by Prony fitting method.Base on this,a criterion for the grounding fault line selection can be educed.Secondly,because of the algorithm with enormous computation,the ADSP21369 with powerful calculation ability and rich on-chip resources was chosen as core processor.The CPLD3256 was chosen for simplifying the logic that peripheral devices controlled by ADSP.With that and 51MCU’s excellent control performance,this paper put forward the hardware frame of a multi-processor device with ADSP+CPLD+51MCU structure.The central control and data acquisition module,with the core of ADSP and CPLD,realized the acquisition of zero sequence voltage and current,the extraction of high-frequency part within zero sequence transient,the selection of fault line and the recording of the waveform.The human-machine interaction module,controlled by 51 MCU,realized the device settings,displaying the information,external communication and other interactions between the human and machine.Besides,the design of switch output module,switch input module,signal-conditioning module and backboard are presented detailedly in this paper.Information exchange interfaces for RS232 serial port,Ethernet,GPS and 485 equipment networks were designed as well.Finally,parts of the function of the fault line selection device were tested according to the design requirements and specifications.The results illustrated that the line selection algorithm based on Prony method has definite practicability.It also showed that the device has good operability and can select the fault line rapidly and accurately,that means the device meets the design requirements.