Research On Earth Fault Identification And Arc-overvoltage Suppressor Operation Control In Distribution Networks

How to identify line single-phase-to-ground faults and transformer internal faults is an important subject in arc-overvoltage suppressor grounded power system. Arc suppression coils were not needed in arc-overvoltage suppressor grounded power system. When the line single-phase-to-ground fault occurs, the arc-overvoltage suppressor operates timely and the arcing ground fault is changing into ground fault with very low transition resistance. There is therefore no arc damage at the point-of-fault. Compared with arcing ground fault, the ground fault with low transition resistance is easier to tackle. When the line single-phase-to-ground fault occurs, the arc-overvoltage suppressor operates to make the ground-fault arc suppressed. But once the fault occurs in transformer windings, the arc-overvoltage suppressor still operates which may bring about short-circuit in the windings of transformers, and further more it could lead to transformer explosion. So how to identify line single-phase-to-ground faults and transformer winding faults and ensure the spark catcher operates correctly and rapidly is becoming an important subject to realize security and stability in arc-overvoltage suppressor grounded power system. The thesis aims to find the shortages of the traditional identification methods, and to develop some novel grounding faults identification methods in arc-overvoltage suppressor grounded power system. And according to the identification result, the arc-overvoltage suppressor is controlled to work.In order to improve the precision and reliability of traditional grounding fault identification methods for arc-overvoltage suppressor grounded power system, by analyzing the characteristics of zero sequence current and negative sequence current of the transformer and feeders, a novel fault identification method respectively based on the zero sequence current and negative sequence current is proposed. By calculating the amplitude ratio of feeders sequence current to transformer sequence current, the identification criterion is built to identify line single-phase-to-ground faults and transformer internal faults. Also the phases of zero sequence current and negative sequence current in the conditions of line faults and transformer internal faults are analyzed. The phase differences of feeders and transformer can identify line fault and transformer internal fault. What’s more, considering about the relationship of the zero sequence current and the zero sequence voltage derivative, a novel fault identification method based on correlation analysis is proposed. The method can make use of not only the steady state characteristics but also the transient characteristics. In order to describe the fault state fully, a novel identification method based on multi-information fusion is proposed. The method has advantages of the above four identification methods. Considering about the effects of asymmetric system, all kinds of disturbance, the probable wrong recognition may make arc-overvoltage suppressor act and bring about short-circuit in transformer windings. To make sure whether the action is right or wrong, the current of arc-overvoltage suppressor should be calculated. And the fault must be identified again based on the current of arc-overvoltage suppressor. Twice identifications have high precision and reliability.The proposed novel identification methods in arc-overvoltage suppressor grounded power system can effectively identify the line single-phase-to-ground faults and transformer internal faults and the arc-overvoltage suppressor is controlled to work. It can protect the total (100%) windings of a transformer and transformer burning resulting from wrong arc overvoltage suppressor operation is avoided. The line single-phase-to-ground faults and transformer internal faults simulation model is developed and the proposed identification methods are verified by MATLAB and EMTP simulation.