High Impedance Fault Line Selection Method Based on Inner Product Projection of Different Time Periods for Flexible Grounding Systems
Wang Xiaowei1, Liu Weibo1, Guo Liang2, Liang Zhenfeng1
1. School of Electrical Engineering Xi’an University of Technology Xi’an 710048 China; 2. Electric Power Research Institute State Grid Jiangxi Electric Power Co. Ltd Nanchang 330000 China
Abstract：High impedance faults are a common form of distribution network faults, accounting for about 5% to 10% of medium voltage distribution network faults, often accompanied by arcing, which can easily cause safety hazards. Due to the weak fault characteristics of high impedance faults, most faulty feeder detection methods only have high accuracy for low-impedance faults. This is insufficient to support the principle of proximity and fast isolation of ground faults. Recently, some high impedance fault line selection methods have been proposed, but most of them suffer from complex principles, single criteria, and equipment measurement accuracy that does not meet the demand. To address these problems, this paper proposed high impedance fault line selection methods based on inner product projection of different time periods for flexible grounding systems. It can accurately detect the faulty feeder at high impedance faults through the characteristic quantities of voltage and current before and after small resistance input. Firstly, the inner product projection of each feeder’s zero-sequence current after small resistance input onto the bus zero-sequence voltage before small resistance input is constructed as criteria 1. Secondly, the inner product projection of each feeder’s zero-sequence current after small resistance input onto the neutral point zero-sequence current before small resistance input is constructed as criteria 2. Finally, when the results of the faulty feeder determined by criterion 1 and criterion 2 are the same, the final faulty feeder result is obtained. The fault detection method fully uses the fault characteristics under different time periods, solves the influence of bus zero-sequence voltage drop after small resistance input and a single criterion on the detection accuracy, and greatly simplifies the faulty feeder detection principle, resulting in a highly accurate faulty feeder detection method. The simulation results using a flexible grounding system show that. Firstly, the faulty feeder can be accurately determined under high impedance fault conditions considering different fault feeders, fault distance, fault initial phase angle, overcompensation, ground resistance and noise interference. Second, considering asynchronous sampling and missing data, where asynchronous sampling is up to 11ms and data missing is up to 85%, the proposed method still has good stability. Then, the accuracy of the proposed method is verified under three arc parameters. Finally, the proposed method is compared with two flexible grounding system methods under four complex operating conditions, where a current transformer reversal was considered, the proposed method takes the shortest time of 0.05 s, and there is no misjudgment. The following conclusions can be drawn from the simulation analysis: (1) Compared with existing methods, the proposed method greatly simplifies the principle of detection criterion and effectively overcomes the bus zero-sequence voltage reduction problem. Therefore, it is appropriate to use different time periods of fault characteristics. (2) The proposed method combines the inner product projection of each feeder current after small resistance input onto the bus voltage and neutral point current before small resistance input. It uses two types of criteria, both of which complement each other to improve the accuracy of fault feeder determination. (3) The proposed method is more capable of adapting to complex working conditions, and the calculation time of the criterion is short. In addition, the faulty feeder can still be accurately determined when the current transformer is reversed.
王晓卫, 刘伟博, 郭亮, 梁振锋. 基于不同时段内积投影的灵活接地系统高阻故障选线方法[J]. 电工技术学报, 2024, 39(1): 154-167.
Wang Xiaowei, Liu Weibo, Guo Liang, Liang Zhenfeng. High Impedance Fault Line Selection Method Based on Inner Product Projection of Different Time Periods for Flexible Grounding Systems. Transactions of China Electrotechnical Society, 2024, 39(1): 154-167.
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2024, Vol. 39 
