Research On New Equipment Of Fault Line Selection In Small Current Grounding System

With the advantage of high reliability for power supply, low tripping and varyingdegree of protection for power grid and its equipment, The small current groundingsystem is widely used in the power of3kV~66kV voltage level in China. However, whengrounding fault occurs, fault line selection still remains a difficult technical problem dueto the fact that the single-phase grounding fault current of the small current groundingsystem is very little, and the fault feature isn’t distinctive. It is very necessary to develop anew equipment of the small current grounding system for fault line selection due to thedevelopment of fault line selection device is relatively backward, and being lack ofadvanced and mature technology products on the market.Firstly, focusing on the fault in the small current grounding power system, this paperanalysis the fault features and studies about all kinds of relevant fault line selectionprinciples and adopts a comprehensive decision-making criterion which is based on themulti-line selection algorithm. This criterion has improved the reliability and validity ofthe device.Secondly, to achieve functions of the fault line selection device, the paper detailedthe design of its hardware platform and software processes. As the amount of data that thecomprehensive decision-making criterion needed is great, the hardware structure of thedevice is advanced. To meet the demand, this paper designs a fault line selection devicewith a multi-CPU system, whose hardware platform is the combination of the ARM withstrong control ability and the digital processing DSP with high operating speed. This paperdetailed designs a central control module, an acquisition module, and a HCI module. Thecentral control module and HCI module centers on ARM, and the relevant software isresponsible for fault line selection, the overall internal control, providing synchronizationpulses, external communications and human-machine interface, etc. The acquisitionmodule centers on DSP, and the relevant software is responsible for the acquisition ofvoltage and current in power system, monitoring the grid fault, extracting zero sequencecurrents including transient and steady states and fault identification pretreatment, etc. Finally, the paper elaborates the functional verification of fault line selection devicevia a static distribution network simulation system, and analyzes the experimental data.The results show that this fault line selection device has good running stability, highadaptability and the fault detection is fast and reliable, which can be applied in practice.