The new frequency difference based Out of Step protection for multiterminal transmission system

The paper presents the novel method of Out of Step protection in multiterminal HV transmission system. The new approach takes advantage of synchrophasor measurements dispersed within the system. The measuring data are used to execute multi point-to-point detection algorithm. The method based on the phenomena that during loosing of system stability, the difference of voltage and current frequency in each affected system point appears. Additionally, the frequency difference is variable according to the distance of the measurement point from the electrical system centre during out of step condition. This feature allows for exact determination of the position of the electrical system centre within the protected power system. It is also important to notice the prediction features of the new method. It reflects in great speed of the phenomena detection. During investigations, the main efforts were focused on the development of new protection techniques to ensure better (faster and more selective than currently known) detection of Out of Step phenomenon. The method was fully tested with utilization of IEEE 14 bus system, simulated in almost 2000 cases. In the article the new approach with exemplary results is presented.