Performance comparison of LOE protection of synchronous generator in the presence of UPFC

Generator loss of excitation (LOE) protection is a principal protection of power system which operate based on impedance measurement. This relay calculates impedance by measuring voltage and current at the generator terminal. On the other hand, the presence of unified power flow controller (UPFC) in transmission lines changes measured voltage and current signals during loss of excitation. In this paper, the impact of UPFC on the performance of LOE protection has been analytically investigated. Afterwards, using modeling results, it has been attained that the presence of UPFC leads to the drastic delay on the performance of LOE relay. This delay results to the overloading and damaging of armature winding of generator. It is also shown that in partial LOE presence of UPFC causes under-reach of the relay. Finally, the phasor measurement units (PMUs) based method has been proposed to reduce the effect of UPFC on the LOE protection. The results indicate that using this new method, the delay of LOE relay has been reduced. In the surveys conducted, various conditions of the power system have been considered.