| Recently, with the pace of economy, keeping power system stable becomes more and more important. As the lightning is the major cause of transmission line outage, the lightning online monitoring on the transmission lines and its related applications have been emerged as the research focus in the field of online monitoring, and the lightning current online monitoring study has attracted much attention from the lightning protection experts. The lightning current online monitoring method based on differential-integral loop has two unique advantages, namely, contactless safe measurement and accurate full-wave record, which can safely, reliably and disconnectedly obtain the lightning current waveforms on the phase wires with the promise of accurate measurement; in the meantime the lightning current full-wave measurement on the transmission line as the foundation of lightning protection study provide accurate original data and show great promise in the field of lightning strike fault identification, lightning parameters inversion calculation and making the differentiation lightning protection countermeasures of transmission lines, Insulation cooperation design and so on. Therefore, the modified methods based on differential-integral loop of lightning current monitoring fault Identification and inversion on transmission lines are investigated in this study, which can greatly boost the development of lightning current full-wave online monitoring and its application on the transmission line.However, the method of lightning current monitoring on transmission lines based on differential-integral loop has to be indicated before the extensive application.In response to the unique measurement of lightning current, it needs to search for the related lightning strike fault identification method and lightning parameter inversion method, which can hugely broaden the application field of lightning current online monitoring system based on differential-integral loop. For this purpose, this work has conducted the in-depth study on the methods based on differential-integral loop of lightning current monitoring fault Identification and inversion on transmission lines with the support of national natural science foundation in general project(grant No. 51177176) and the science and technology fund of Yunnan power grid corporation(grant No. K-YN2012-200). The major achievements are as follows:â‘ To make up the disadvantages of traditional differential-integral loop with large random winding density and the contradiction between sensitivity and frequency band, the modified lightning current sensor based on PCB differential-integral loop was indicated, which had theoretical bandwidth of 14 MHz, measured differential signal at a high sensitivity( up to 2V/ k A) and accurately restored the measured current waveform combined with the help of digital integration technology. The test results showed that with the contactless measurement distance of 1.4 m it can obtain the lightning current waveforms accurately(Average measurement error is only 3.05%). The lightning current online monitoring system based on differential-integral loop was established and installed on the 110 k V transmission lines so that some field current waveforms were obtained.â‘¡ The frequency analysis method for ADF-EMS software was used to study the effect of lightning channel speed, incident angle and tortuosity on the magnetic field of observation point where the were installed. Based on it, the three dimension multi-tower model system using ADF-EMS software was established. The magnetic field situations at the observation points under four classic lightning strike fault types and the effect of lightning channel on the measurement results obtained by differential-integral loop were analyzed and discussed, respectively. The multi-tower system model by using EMTP-ATP software considering the effect of impulse corona was established, and the time-domain waveform of lightning transient current at observation points under 13 kinds of different lightning strike fault types were acquired and analyzed.â‘¢ The lightning current waveforms at the observation points with 13 kinds of different lightning strike fault types were selected as the simulation experimental subject, the fault clustering fingerprint of lightning current signal energy characteristics was constructed, and the lightning current fault pattern clustering method based on Mahalanobis distance theory was indicated so that the lightning strike fault types could be classified into three classed preliminarily. The 3-D distribution figures of S-matrix and frequency spectrums based on S-Transform theory with all kinds of fault types analyzed so that the characteristic quantities were put forward. Therefore, the direct lightning strike fault identification method based on Mahalanobis distance and S-Transform was presented.and applied to the field lightning current waveforms successfully.The test show that the correct rate of the different types of lightning fault validation sample is higher than 90%, and this identification method were applied to the 4 cases of lightning current waveforms of lightning current online monitoring fault identification method based on differential-integral loops successfullyâ‘£ Combining with the existing lightning location algorithm for measured data by differential-integral loop, the numerical inverse transformation, time domain convolution and spline interpolation are adapted to establish the lightning waveform inversion method. And by using the simulation data, at the angle of statistics, the lightning current amplitude inversion method for different lightning strike type is established. Therefore, the lightning current inversion technology for transmission line which were made up by the amplitude inversion and the waveform inversion method was put forward. The simulation shows that the lightning current full-wave inversion method is effective and feasibleIn summary, this paper presented a modified lightning current monitoring senor based on PCB differential-integral loop, which can overcome the disadvantages of the original differential-integral loop. Then, the multi-tower model systems by using ADF-EMS software and EMTP-ATP software, respectively, which was used to study the effect of lightning channel on the magnetic field at the observation point where the differential-integral loop were installed, and the numerous lightning current at the observation points of direct lightning strike fault types were obtained. After that, the direct lightning strike fault identification method based on Mahalanobis distance and S-Transform and the lightning current inversion method for transmission line based on the differential-integral loop measurement were presented, respectively, which provided the necessary proof and technology support for the extensive application of lightning current online monitoring system based on differential-integral loop. |
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