Fault Line Selection And Fault Location Of Resonant Grounded System Based On The Transient Characteristics

With the development of the economic and the construction of cities in our country, the topology of the distribution network is becoming more and more complex. Due to a large number of cable lines have been used in the distribution network, the capacitance current to the ground has a sharp increase. Therefore, the resonant grounding system has been widely used in the distribution network with the low voltage in order to eliminate arc effectively. The ground current has been compensated using the arc suppression coil in the neutral point but it is easy to develop a short-circuit fault of single-phase ground to a multi-point ground for the permanent fault. At the same time, are grounding not only can cause over voltages of the system, but also can damage the equipment and destroy the safety of the system. Therefore, it is significant to find the fault line and fault location and remove the fault in time. Although the arc suppression coil improves the reliability of power supply, the steady-state characteristics of electrical quantities is not obvious because of the weak fault current due to the compensation effect of the coil when the distribution network has been in a single-phase ground fault. The traditional methods based on the magnitude and direction of the failure fundamental can not be applied to the resonant grounding system. Therefore, fault detection of the resonant grounding system is more difficult.The fault line selection and fault location of the resonant grounding system in the distribution network have been researched in this paper. Because the arc suppression coil compensated the amount of the fundamental, the transient contains a lot of fault information after a fault. Therefore, the transient characteristics are the focus of this study. Firstly, a model of a35kV distribution network with4feeders has been built in PSCAD/EMTDC. The characteristics of the spectrum during the charge transient process and discharge transient process have been analyzed when a single-phase ground fault occurred in the resonant grounding system.Secondly, a new approach to detect fault line in the resonant grounding system using curve fitting based on zero sequence transient voltage and integral charge has been proposed. Theoretical analysis shows that the relationship between the zero sequence transient voltage and zero sequence transient integral charge on the health feeders is straight-line, while it is an inegular curve on the fault feeder. The conclusion has been proved with the simulation in different fault location, different fault resistance and different fault phase angle by comparing the relationship of zero sequence transient voltage and integral charge in the two-dimensional image. Taking decreasing manual intervention and automation implementation into account, a method of fault line selection based on curve fitting of zero sequence transient voltage and integral charge has been proposed. This method achieves mathematical quantization of the criterion that is based on the relationship between transient voltage-transient integral charge by determining the slope coefficient and fitting of feeders. The results of simulations show that the method can find the fault line accurately in the conditions of high-impedance, high noise and arc fault.Finally, a method of fault location based on transient characteristics of charge-discharge transient has been investigated on the basis of the fault line selection. According to the change of the spectrum in the charging transient process and discharge transient process, it analyses the physical process theoretically that forms the transient frequency in the charge-discharge transient. Consider that the distribution network has many feeders, it has many refraction and reflection in the traveling wave during the charging transient. A method of fault location based on transient characteristics of charge-discharge transient has been proposed. Firstly, the program extracts the transient signals with charging frequency by wavelet filters. Secondly, it calculates the fault distance preliminarily to estimate the range of characterized path frequency. Finally, it can get the more accurate results through the relation between the characteristic path frequency and fault distance. The effectiveness of the method has been proved by the simulation in the different condition of the fault. Through the combination of the charge and discharge transient. It can identify the characteristic path frequency effectively during discharge frequency bands. This proposed method avoids the effection on the accuracy of the fault location with different fault resistance and fault distance during the charging transient.This paper aims to solve the problems of fault line selection and fault location in the single-phase ground fault of the resonance grounding system. It studies the transient characteristics of the resonance grounding system in order to identify the characteristic differences between the fault feeder and the health feeder, explain the physical relationships between transient characteristics and fault location of the feeder, and find the mathematical relationships between them. It is expected to form a set of scheme on the fault location in the resonant grounding system based on the transient characteristics.