Smart grids have become an inevitable choice for international power development. State Grid Corporation of China has proposed to fully build a smart grid by 2020. In order to adapt to the functional requirements of the smart grid with information and automation characteristics, this project carries out key technical research and engineering practice in online monitoring methods and system development, which is an important characterization of the power grid operating state-transient (process) overvoltage.

1. Main research contents

1. A back-calculation method based on the monitoring system transfer function, FFT and IFFT is established to realize the back-calculation of transient overvoltage waveform signals using the monitoring voltage or current signals. The transient voltage dividing system established based on digital simulation module, MOA and counters shows that the back-calculation method can be applied to practical projects.
2. Based on the 500kVCVT of Wuxi Rixin Factory, the overvoltage transfer was tested and studied. The output from the outgoing terminal of the intermediate transformer secondary winding under the action of lightning impulse, the output from the terminal with harmonic measurement, and the series connection of the self-made large-capacity high-frequency non-inductive capacitor C3 The waveform characteristics of the output at both ends were analyzed in the time and frequency domain. The results show that the overvoltage waveform distortion output from both ends of the homemade C3 in series is small, and the peak voltage division ratio and the system transfer function of the voltage divider formed with the traditional CVT are stable. This voltage dividing method is suitable for transient overvoltage monitoring in ultra-high voltage power grid systems. In addition, the impulse test data of the voltage dividing system was used to verify the back-calculation method, and the analysis results once again confirmed the practicality of the back-calculation method in transient overvoltage monitoring technology.
3. Based on CVT, a 500kV transient overvoltage online monitoring system network and data processing and analysis center has been established. It mainly consists of a single-wire three-phase monitoring subsystem in the substation, network transmission and a central computer. The single-wire three-phase monitoring system consists of a CVT with a C3 transient overvoltage monitoring unit, a transmission cable, and an intelligent transient monitoring and data analysis system.
4. Build power frequency and operating impact test equipment in the laboratory, switch action simulation tests (three-phase single division and single closing, reclosing and dividing, three-phase live single-phase single division and single closing, reclosing and dividing, and three-phase live single-phase coupled operating waves), and conduct performance test on the transient monitoring system.
5. Finally, the on-site installation and screen erection were carried out in conjunction with the "Pingyao 500kV Substation String Allocation and Adjustment Project", and the start-up and debugging of Yaoyang 5438 Line was carried out to verify the functions of the system and the reliability of field operation. Since its operation, the device has monitored and recorded a large number of rich transient overvoltage waveforms of the power grid.

2. Main results
   The main achievement of this project-the intelligent power grid transient insulation coordination real-time analysis system has been installed and put into operation on East China 500kV Pingyao Transformation Line 5438.
   The key technical problems solved, technological breakthroughs and core technologies achieved during the research and development process of this project are all independent innovation technologies. Among them, 8 utility models have been authorized; 2 invention patents have been accepted and 1 software copyright has been authorized. Published 5 papers at home and abroad, and searched 1 article by SCI.

3. Acceptance status
   On February 28, 2012, State Grid Corporation of China entrusted the East China Branch to hold a project acceptance meeting in Shanghai. The expert group headed by Professor Wang Xifan (academician of the Chinese Academy of Sciences), an expert on power systems at Xi'an Jiaotong University, listened to the project's work, technology, scientific and technological inquiry and application certification reports. After discussion, it was agreed that the research results of the project had reached the international advanced level.