Comparison study among the different existing loss of excitation protection schemes in synchronous generator

Synchronous generator is the most important element of a power system and its fast and reliable protection is crucial. One of the most abnormal conditions in a generator is loss of excitation (LOE) which is harmful to both the generator and the power system. This condition should be detected and the generator isolated from the system to avoid generator damage as well as power system instability. This work presents an experimental study and comparison of the two conventional LOE protection schemes, negative-offset and positive-offset mho element under different conditions. The results show that the two schemes can detect LOE fault under total or partial LOE conditions, however in terms of speed (fault detection time) the positive offset scheme is faster than the negative offset scheme under all loading conditions. Besides, the two LOE protection schemes are reliable and do not operate under power swing disturbances caused by any type of external faults.