Research On Identification Of High-voltage Lighting Overvoltage On Transmission Lines Based On Wavelet Transform

Lightning overvoltage is a major cause of line fault, as it may lead to insulator breakdown in high-voltage transmission lines. Different types of lightning overvoltage shall resort to different lightning protection measures, the identification of which provides a crucial reference to the arrangement of lightning-proof devices to ensure the economy of grid construction, and is of great significance to the configuration, failure forecast, and maintenance of relay protection in high-voltage transmission lines.Based on the method of power system transient stability analysis, the thesis analyzed the reasons of fault in transmission lines caused by lightning, classified different types of overvoltage accordingly, and developed a mathematical model of lightning electromagnetic pulse. Besides, a model of high-voltage transmission line with corona was established by employing ATP-EMTP software. Then, a wavelet transform filter was developed with the help of MATLAB software to analyze and process transient signal. According to both the energy ratio of wavelets and wavelet modulus maxima, seven distinguishable values were extracted. Therefore, the identification of different types of overvoltage falls into the following three steps:1. The identification of lightning overvoltage that caused fault or didn’t and the overvoltage result from short-circuit;2. The identification of direct lightning stroke overvoltage and lightning-induced overvoltage in lightning overvoltage that caused fault;3. The identification of back striking and shielding failure in direct lightning stroke overvoltage.The thesis introduced a comprehensive identification system by referring to the distinguishable values, and proposed an adaptive threshold correction strategy on the basis of rich practical operating experience. At last, by applying the system to the analysis of overvoltage signals detected in real circumstance, the effectiveness and reliability of the strategy was testified. Compared with previous identification strategies, it is easier to operate as guided by simple principles, and has high accuracy by comprehensive identification. Moreover, it is adaptive to different operation conditions and environment.