Research Of Resonant Ground System Fault Line Detection Technology Can Be Applied To HIF

When single-phase grounding fault happens in small current grounding system, ground current is small and the line voltage remains constant, so power can be continued in 1 to 2 hours, which is the reason why it is widely used in Chinese 6-66KV medium voltage distribution network. Recent years, with the continuous expansion of the distribution network scale, increase of the total length of line and widely use of cable, the capacitive current of system and single-phase grounding fault current increases, which makes resonant grounded system become the mainstream of Chinese distribution network gradually.Non-fault-phase voltage rise to (?) times that in normal when single phase grounding fault happens in small current grounding system, which threatens the insulation of system. Therefore, it is of great importance to find fault line timely. Currently small current grounding fault line selection system can be roughly divided into two categories:passive and active method. The passive method detects the fault line according to certain features generated by single-phase grounding fault while active method determines fault line by injecting signals to system. The compensation of Peterson-coil in resonant grounded system makes detect fault line more difficult for passive method by diminishing fault current. Active methods make use of external signals to reduce the difficulty of fault line selection which overcomes the limitations of the system structure. But active methods also have drawbacks such as need additional equipment and single frequency of fault line detection signal. Especially for large fault impedance, the active methods are unable to do as well as common fault because strength of fault line detection signal decreases and shunting effect of non-fault is obvious.A resonant grounded system fault line detection method without additional signal injection device is proposed in the paper. When single-phase ground fault occurs in a feeder, a disturbance signal with various frequency components is generated by controlling thyristors switching damping resistor in series with Peterson-coil which equals to switch on damping resistor for a short time. The fault line is determined by analyzing the disturbance current of every line with the detection criterion proposed in the paper. This method requires no additional signal generating device and has rich frequency components in pulse signal. And most important of all, it can be applied to high impedance fault line detection. Theoretical analysis, simulation analysis and laboratory experiments all verify the reliability of the method.In Chapter I, the background, significance and current research status of resonant grounded system fault line detection are introduced. Chapter II theoretically analyzes the proposed fault line detection method and derives the analysis circuit and mathematical expression of pulse signal, which makes it possible to compare the disturbance current expressions and frequency components of fault line and normal line. Chapter III verifies the effectiveness of the propose fault line detection in overhead line system and cable mixed system in Simulink, MATLAB respectively. The influence of the method to fault current and the selection of delayed triggering angle are analyzed with the simulation results. The affecting factors of fault line detection pulse signal frequency components are also demonstrated. Chapter IV further verifies the effectiveness of the proposed method by laboratory experiments. Chapter V summaries the research work.