Characteristic Study And Simulation Analysis Of Harmonic Wave For High Voltage Transmission Line

With the rapid economic development and the expansion of power grid in China, the society is demanding for a more quality and reliable power supply. In normal power system, the waveform of voltage and current ought to be sine wave under mains frequency. However, actually ultraharmonics often mingles in due to wave distortion. In recent years in particular, the wide application of commutation devices as well as the popularity of electronics, have resulted in a severe waveform distortion in power system, which produces a lot of ultraharmonics and brings harms to various power equipment, communication lines and users. On the other side, high-frequency signals caused by fault contain richer information than mains frequency signals, such as the type, direction,location and duration of the fault. Such information runs throughout the signals. Therefore, through analyzing and studying the rich high-frequency elements in fault signals, we can obtain more information and ensure the reliable action of protectors.After a review upon the transient state of power system, this paper figures out fundamental characteristics, harms and influences of harmonics when a fault occurs, gets hold of basic methods for analyzing harmonics and lays a theoretical basis for follow-up studies. Then the working principle and functions of common digital filters are elaborated. Digital filters (m file)are designed with MATLAB software and the filtering effect of the filters are comparatively studied with interactive signal processing window. Meanwhile, based on the analysis of zero-sequence current signals, the use of elliptic low-pass filter is suggested, and data analysis indicates that filters have reduced the influence of ultraharmonics upon traditional protections. Finally, traditional protection mode in high-voltage transmission line and the principle of transient-based protection is studied and analyzed,500kV long-distance transmission line is stimulated and digital high-pass filter is applied. Through data comparison, it proves that signals after filtering processing is conductive to the reliable action of protectors in a transient state.This paper takes the transmission and transformation project from Yang Cheng City, Shanxi Province to Jiangsu Province as an example, conducts analogue simulation with relevant parameters, and uses tools like wavelet analysis to calculate and analyze. Based on the result, several suggestions are put forward to provide a guide for the analysis and use for harmonics, as well as the relay protection in high-voltage transmission lines.