Ferroresonance Identification Technology Based On Rrough Set Theory And Research On The Effectiveness Of Harrnonic Elimination Measures

Ferromagnetic resonance caused by saturated Electromagnetic Voltage Transformers often occur in the system neutral point isolated. It can endanger the voltage stability and safety of electric equipments.PT core saturates easily in the power system over-voltage conditions, inductance is nonlinear and reduces quickly, then resonant with capacitor. The resonance can occur at high frequency, basic frequency and low frequency. Ferromagnetic is easy to burn high voltage fuse, or leads the PT seriously overheating, burning and explosion. But long time ferroresonance makes the three-phase voltage rise too long, line arrester explosion phenomenon is common and the line insulation breakdown phenomenon also happen from time to time. The PT resonance which makes neutral point voltage displacement and products zero sequence voltage, is similar to the single-phase-to-earth fault, and is easy to make the small current grounding system insulation and monitoring device send wrong signal. The wrong signal would bring the operating personnel wrong results for processing as single-phase-to-earth fault line selection, lead to the expending of the fault. Besides, the identification technique for ferromagnetic resonance fault,single-phase-to earth fault and PT disconnection fault is not perfect.This paper briefly analyzes the reasons of ferroresonance resonance generated conditions, characteristics of single-phase grounding fault and basic characteristics of PT disconnection fault, puts forward a method of distribution network fault identification based on rough set theory.PT current can not be monitored, which affects the identification of the ferromagnetic resonance and other faults, so according to different PT phase current features under different faults, this paper designed and developed a PT monitoring-and-diagnosis system.In this paper, we compared the most commonly used three kinds of harmonic elimination measures (primary winding neutral point voltage transformers series resistance grounding harmonic elimination,4PT method, open delta winding is connected with a damping harmonic elimination resistance) with simulation and analysis in detail using ATP simulation program, found that the current harmonic elimination measures are not perfect, so we need to develop better techniques and equipments. Based on ATP simulation, this paper designed and developed a new harmonic elimination device, mainly introduces the CPU chip, FPGA chip, the signal acquisition system, device anti-interference design etc.. The device overcomes the traditional small current device product defects, and this paper introducts the design schemes of device modules.