Study Of Fault Line Selection Protection In Small Current Grounding Power System Of Substation Of GUIYANG HUAXI

The low current grounding mode of the neutral point in the power distribution network is adopted in Huaqi of Guiyang,which has a lot of advantages. However, the fault characteristics are not obvious with this kind of grounding mode when the single-phase grounding fault happens , as a result the selection of the faulty line is very difficult. If we can find out a way to select the faulty line as quickly as possible, it will do a lot of good in the reliability and continuances of the power supply. During these years, researchers put forward lots of schemes, and many types of equipments were applied in the operation too. But the effect is not so good from the applying situation at present; it is a difficult problem that has not been solved in recent years. This paper summarizes the principles of the existed faulty line selection methods and schemes, bases on them, the paper analyzes the limitation of the exited schemes and brings forward some questions need to be solved. This article analyses the transient character when the single-phase grounding fault happens in the low current grounding system, advances a faulty line selection method by using of wavelet transform that has nice time-frequency local characteristic to pick-up transient information. When the single-phase grounding fault happens, the transient component of the current of the grounding current transformer is several to decades times to its steady value. The wavelet analysis theory is able to process the mutational, weak, non-stationary faulty signals; by using this algorithm, the question of the low accuracy of traditional line selection methods can be solved. All kinds of fault situations are analyzed in the paper, according to the analysis results, the paper presents software and hardware design of the low current grounding faulty line selection equipment, puts forward some technique requirements of the hardware design. According to the applying expectations in practice, this paper decides to use industrial computer as the hardware platform for this line selection device. By using his scheme we can save developing time and mainly focus on the algorithm research and questions we may have to face in the application. When grounding fault happens at the time when current is zero, the transient value is too small, in order to prevent it, the paper brings forward the current increment method to select faulty line. It covers the shortage of single line selection ways and satisfies the need in the practice application. Theory analysis and lots of simulation experiments prove that the method presents in the paper is accurate, reliable and of nice effect. In order to improve the reliability and precision of the device, the paper presents some engineering processing methods and uses modular programming idea. It provides advantages for the programming debugging, linking, transplanting and updating, as a result the structure of the software is clear, compact and logical. The device realizes many functions, such as the real-time detection, faulty line selection, faulty recording and fault alarm and so on, it can meet the specifications in the practice operation. The device assembles basing on the industrial computer, it satisfies the specific requirements of the transient algorithm to the hardware, the experiments show that this device is of great applying value.