Resonant Grounding System Fault Analysis And Line Selection

The resonant earthed system is popular in power distribution networks. The problem of fault line selection for single-phase-to-earth faults in resonant earthed system is one of important topics to the protective relaying. In the neutral ungrounded system, The frequent ferroresonance over-voltage would seriously affect the operation safety in electric power system. Resonant earthed system can also partly become neutral ungrounded system because of improper operations. In this thesis, the problem of fault line selection and ferroresonance over-voltage in resonant earthed system are studied. The majority work and achievements in this thesis are as follows:(1) It is analyzed that the quench principle of arc suppression coil, the displacement of the neutral voltage and the fault transient course when single-phase-to-earth fault occurs in resonant earthed system. The paraphase of zero-sequence transient power is studied.(2) The unit length RLC parameters of three canonical aerial conductor arrangements are calculated, a typical radiate resonant earthed system is set up. Then MATLAB is employed for corresponding simulation.(3) The principle of ferroresonance over-voltage is introduced. The frequency division ferroresonance is laid emphasize to analysize. The frequency division ferroresonance has largest resonant extent, is easy to be exited and can cause most accidents. The primary measures to eliminate ferroresonance are introduced. MATLAB is employed for the simulation of ferroresonance over-voltage. The simulation results prove that the arc suppression coil is capable of efficiently eliminating the ferroresonance over-voltage.(4) The problem of line selection of single-phase-to-earth fault in the resonant earthed system has not been well settled for a long time, this thesis summarizes the present line selection techniques, analyzes their applicable conditions while expatiating the principle of line selection. Based on this, analyzes the development directions of line selection techniques in future.(5) Construct a 50Hz digital notch, filter out the power frequency component from the sampled signals of each feeder's transient zero-sequence current, obtain the transient component of each feeder's zero-sequence current. An adaptive line selection method and amethod with correlation analysis based on the transient component of zero sequence current have been proposed. Theoretical analysis and simulation results demonstrate that the result of fault line detection using the two methods are accurate and reliable and the protective margin has been further enhanced.(6) A method for distinguishing ferroresonance and single-phase-to-earth fault in the neutral ungrounded system or single-phase-to-earth fault and series resonance in resonance earthed system is studied. A integrative project is presented which integrate fault type distinguishing, automatic tuning of arc suppression coil and fault line selection. Once neutral voltage exceeds 15 percent of rated phase voltage, according to the result of fault type distinguishing, the equipment is capable of automatically taking the corresponding operations.