Analysis and Suppression of Voltage Transformer Fusing Mechanism in 20 kV Distribution Network
Yang Ming1, Shi Yifeng1, Sima Wenxia1, Liu Yao2, Xia Zipeng2
1. State Key Laboratory of Power Transmission Equipment Technology Chongqing University Chongqing 400044 China; 2. Zhuhai Power Supply Bureau of Guangdong Power Grid Co. Ltd Zhuhai 519000 China
Abstract To cope with the rapid growth of urban power load and density, 20 kV distribution networks have been put into use in Suzhou, Shenzhen and other places, becoming the development trend of medium voltage distribution networks in major cities in China. The frequent occurrence of voltage transformer (VT) fuse blowing accidents in 20 kV distribution networks affects the safe and stable operation of the system. Due to power supply requirements, the length of cables in 20 kV distribution networks is extremely long, and the capacitance to ground is large. The ratio of capacitive impedance to inductive impedance in the system is much smaller than the range specified in the Peterson resonance criterion, resulting in a fundamental change in the electromagnetic energy interaction mechanism of the system. Ferroresonance will no longer occur, which is significantly different from the fault transient in traditional 10 kV distribution networks. However, existing research has overlooked the nonlinear excitation characteristics of VT, and has not yet conducted in-depth analysis of the electromagnetic energy interaction mechanism and influencing factors in this process, making it difficult to support research on suppression measures and leading to difficulties in preventing VT fuse blowing accidents. Therefore, this article aims to reveal the mechanism of fuse blowing accidents on VT primary side in large-scale distribution networks and propose targeted suppression measure. Based on a actual 20 kV distribution network, the fault energy interaction circuit is extracted, and the process of cable to ground capacitance discharge after a short circuit is analyzed. Establish a nonlinear differential equation for the process of cable capacitance discharging to VT, characterize the nonlinear excitation characteristics of VT based on the principle of piecewise linearization, obtain segmented time-domain analytical solutions of VT primary side current for the equation under different states, and compare the error between analytical calculations and simulation results to achieve accurate analysis of the process. Based on the analytical formula of VT primary side current, calculate its angular frequency and time constant, and then analyze the law of VT current characteristics changing from "quantitative" to "qualitative" during the process of increasing the ground capacitance in system, revealing the mechanism of electromagnetic energy interaction throughout the entire process of system fault. Construct a 20 kV system electromagnetic transient simulation model, reproduce the fault waveform of the fuse accident, analyze the waveform characteristics through analytical calculations, reveal the influence of system operation mode on current, and study the risk of VT fuse blowing. Based on mechanism analysis, targeted suppression measures are proposed to suppress the amplitude of VT primary side overcurrent through discharge circuit topology reconstruction. Build a high-voltage test platform in the laboratory, conduct suppression measures verification experiment, further prove the effectiveness and feasibility of the suppression measure proposed in this paper. Research has shown that the analytical calculation results in this article are accurate and can analyze the VT high-voltage side fuse mechanism in large-scale distribution networks. The proposed suppression measures have significant effects and high feasibility, and the research results can support the safe and stable operation of 20 kV distribution networks.
Yang Ming,Shi Yifeng,Sima Wenxia等. Analysis and Suppression of Voltage Transformer Fusing Mechanism in 20 kV Distribution Network[J]. Transactions of China Electrotechnical Society, 2024, 39(23): 7577-7591.
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