Loss of Excitation (LOE) is one of the most critical faults in synchronous generators, which, if not detected promptly, can lead to power system instability and severe damage to the generator. The main challenge in distinguishing LOE from Stable Power Swings (SPS) lies in the time delay, which is a common issue in most recent protection methods. This paper presents a novel method for LOE detection in synchronous generators. The method utilizes a new criterion based on the variation of the generator rotor speed, where this criterion increases above one per unit after the occurrence of LOE and remains in this state. Unlike traditional methods that require complex settings, this approach operates without the need for threshold adjustments, ensuring accurate and fast performance under various conditions. In the simulations, generators of various sizes were subjected to various loads and network scenarios. The results of the simulations, which were carried out in MATLAB/Simulink, verify that the suggested approach not only diminishes the detection time but also preserves high accuracy when system disturbances occur, protecting system stability under severe conditions.