Generator Out-of-Step protection using the trajectory of estimated relative speed

Abstract

The condition where the load angle of a generator changes rapidly with respect to another generator or portion of a system is called Generator Out-of-Step (OOS). The traditional way of detecting an OOS condition is to analyze the trajectory of the impedance seen from the generator terminals. Therefore, setting calculations for these impedance-based methods become more challenging and time consuming. Detailed time domain simulations, which required both generator and system data, are necessary to set up these relays. This paper proposes a novel method to detect an OOS condition of a generator using its relative rotor speed. The inputs for the proposed algorithm are the terminal voltage, current and machine parameters which are readily available for typical synchronous generators. The proposed algorithm monitors the change of relative rotor speed following a fault and declares the OOS condition if the relative speed tends to increase during a swing cycle. This technique is computationally simple, easy to implement, and fast compared to impedance-based methods. The application of the proposed method is investigated using time domain simulations. Also, the sensitivity and security of the proposed method are analyzed under various power system conditions.