The new frequency-difference-based out-of-step protection for multiterminal transmission systems

This presentation describes the novel method of out-of-step protection in a multiterminal HV transmission system. The new approach takes advantage of synchrophasor measurements dispersed within the system. The measurement data are used to execute a multipoint-to-point detection algorithm. The method is based on the phenomena that during losing of system stability, a difference in the 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 the out-of-step condition. This feature allows for the 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 the 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 the out-of-step phenomenon. The method was fully tested with utilization of an IEEE 14 bus system, simulated in almost 2000 cases.The new approach is presented with exemplary results.