This article proposes a real-time, setting-free out-of-step (OOS) protection strategy for a single synchronous generator (SG) connected to a multimachine power system. To do so, the fundamental frequency phasor of the voltage at the generator terminal is measured. It will be shown that at the point of OOS, the imaginary part of the voltage crosses the zero point and becomes negative, whereas the real part of the voltage holds a negative value. On the other hand, it will be shown that during stable power swings, the imaginary part of the voltage behaves as per an OOS event, whereas the real part of the voltage becomes positive. Therefore, this principle can be used as the criterion to detect an SG OOS. Moreover, it will be shown that the proposed principle can count the number of SG pole slip occurrences so that it can trip the generator after a certain number of pole slips. The proposed scheme is a response-based algorithm and uses only locally measured voltage at the relay location. F