Generating steadiness of synchronous generators is highly dependent on their exciter, as the direct current from excitation system sustains generator stator and rotor windings magnetically coupled. However, any excitation system failure grades generator loss of excitation and suspends power transmission from generating unit to customers. It is typically characterized by high active power flow out of the generator with large reactive power flow into the generator. And this power imbalance increases rotor speed of generator beyond synchronous speed which result in voltage and current instability in the grid connected with the generator. At this state, excitation loss protection must isolate the faulted generator from the remaining system to avoid any damage that can possibly happened due to excitation loss. This thesis work studies generator excitation loss relay detection ability on IEEE 9-bus test system and Tana Beles-I power plant on various excitation loss events. The proposed schemes have simulated and evaluated using MATLAB/SIMULINK software. The simulation results show that the relay tripping duration is highly dependent on initial loading condition of the generator, type of excitation loss and reactive power support from interconnected systems. Comparatively excitation loss relay shows a good performance in full loss of excitation than in partial excitation loss. The relay is able to detect any full excitation loss in less than 6.4second after failure initiated. But it detect partial excitation loss long after the failure for heavily loaded generators and not detect at all for lightly loaded generators. On the other hand, the relay has mal-operated for stable and unstable power swings which are failures outside the exciter. To overcome mal-operation of excitation loss relay, a back-up protection scheme has proposed based on study of field voltage, quadrature-axis voltage and generator reactive power variation in excitation loss event. The proposed algorithm limits the reactive power consumption of excitation loss generator considering system stability. The backup protection has improved the excitation loss detection length to twice less for heavily loaded generators and 16% less for medium and lightly loaded generators. It has also differentiate system failures and excitation loss events successfully.