A Research Of Relay Protection Of EHV Transmission Line

Rapid removal of the fault is a main factor for the safety and stabilization of power system. With the pace of construction of smart grid speeds up, in the future, EHV/UHV transmission lines will share the most part of the grid of our country. Because of its special power environment, when the conventional means of protection applied to the EHV transmission lines, it will be easily affected by many factors, such as load current, transition resistance, capacitance current and so on. Fault current protection, because of the advantage on its own principle, it can avoid the influence of many traditional factors, at the same time also have high sensitivity and good reliability. Although it is a good choice to put the fault current protection to be used as the main protection for the EHV transmission lines, it still need some backup protection measures.As a new means of signal analysis and processing, HHT is very suitable for nonlinear signal analysis. A multiple frequency signal can be easily decomposed into a series of single frequency signals by HHT. So we can use HHT to extract the fault signal form the signal which contains a large number of harmonic components. So HHT can be very useful when it applied to transmission line relay protection. But because of HHT’s own method of defects, it is easy to produce modal aliasing. This thesis proposes a way to solve this problem based on EEMD.By the end of the article, this thesis proposes an adaptive protection scheme which combines artificial neural network and traditional current protection. This method can change the protection performance by testing system’s different operation modes and the types of faults to improve the sensitivity of the relay protection.