Faulty Line Selection For Single Phase-to-earth Faults In Neutral Un-effectual Grounded System

The neutral un-effectual system grounded by Petersen-coil doesn’ttrip immediately in the event of single-phase ground fault, therefore thissystem is widely used in low voltage distribution grid because of its highreliability, smaller current at fault point arc and more safety. However, dueto the compensation of Petersen coil, zero-sequence current of the faultline is smaller which results in line selection difficulties. As therequirement of reliability becomes much higher, the study of the lineselection in Petersen coil grounded system is more important. This paperpresents many achievements including:(1)Line selection method using multi-level resistors parallelingPetersen coil. Via the analysis of transient circuit after a system failure, thepaper concludes that multi-level resistors has much influence on the faultyphase and zero-sequence current of the faulty line and less influence on thesound lines. The distribution law of zero-sequence power loss is alsoanalyzed. Based on this, it raises the proposed control strategy anddiscusses the closing time, change cycle and resistance selection.Compared with the traditional shunting resistor method this method has theadvantages of the maximum amplitude of the current existing for a shortertime, a smaller mutation, more line selection flexible and low powerconsumption. Simulation results verify the feasibility of the method.(2) Line selection method based on matrix pencil algorithm andcorrelation theory. Firstly it studies the line selection scheme based on thecorrelation theory, and analyzes the effectiveness and limitations from theory and simulation. The paper studies the modality model identificationmethod by matrix pencil algorithm and the noisy signal processing method.It presents the prediction model based on common high-frequencycomponents of each line which can be compared with the actualhigh-frequency electrical quantities of each line. Finally, simulation resultsvalidate this method.Finally, the paper made a further study summary and outlook.