Analysis Of Power Distribution System Abnormal Operation State And Research On Fault Line Selection Method

The large amounts of power distribution networks take on the basic task of mains power supply to the widespread consumers. Along with the development of society and economy, the demand for power supply and its quality has increased rapidly in recent years. Consequently, it is necessary to analyze the abnormal state and find out the insulation hidden trouble of distribution networks. Besides, faults should be detected rapidly and effectively in order to guarantee the security, stabilization and reliability. Along with the extensive use of power cable lines in power distribution system, the probability of fundamental frequency resonance has greatly increased. It may endanger the normal operation of the power system. On the basis of theoretical analysis and numerical calculations using MATLAB language combined with a real instance, it is indicated that the improper electrical parameter coordination caused by the abundance of power cable lines result in fundamental frequency current resonance, in addition, the countermeasures based on SVC to solve the problem are put forward. Digital simulation results have proved the effectiveness and practicability of the scheme.Small current grounding power system is a popular neutral grounding mode around the world and is widely used in our country. The fault line selection matter in such system is one of the problems, which have not solved successfully for many years.Wavelet analysis theory and its application in power system have been introduced briefly. This paper gives a general overview of various neutral grounding modes. Some existing theories schemes on the fault line selection have been summarized systematically. Then, it presents problems, which should be solved, and conclusions have been made.The fault transient characteristics of single-to-earth fault for small current grounding power system are analyzed in detail, and then a novel algorithm for fault line selection is put forward. This method uses wavelet transform to pick up the transient fault information because of its multi-resolution characteristics and time-frequency localization nature. Fault line is detected based on the modulus maxima or energy comparison under some scale of wavelet transform of phase currents orβcomponent current. This method is applicable for such power system as only furnished with CT on two phases, so the shortcoming of other methods presented in recent years is overcome. Some issues associated with the algorithm such as wavelet function selection, analysis level, and boundary treatment and so forth have been discussed. The stein self-adapting threshold denoising method is used to the signal pretreatment, thus the SNR and resolution are improved. The influences of several factors such as harmonics, intermittent arc grounding, CT, load and fault resistance have been thoroughly analyzed, therefore, it is fundamental work for its application.Theoretical analysis and a variety of simulation results show that the proposed method is accurate and reliable, its applicability and sensitivity are better than the steady method. It is suited for various small current grounding system, furthermore, the robustness and feasibility of this scheme is also testified.