Influence of protection on power quality for system with distributed generation units

Power quality is extensively affected by power system faults. One of the power quality events is the voltage sag. The depth of the voltage sag is determined by the types of fault, fault location, system configuration, and load representation, while the duration of voltage sag can be distinctly impacted by protection systems. In the paper, the accelerated protection strategies are presented to reduce the voltage sag duration. The fixed time delay zone of the relay on the system side can be accelerated depending on the second variations of the current sequence components; which on the distributed generation units side can be accelerated by the undervoltage. Simulation results show that the acceleration of the directional overcurrent protection scheme can effectively reduce the duration of fault, thus reducing the voltage sag duration, and the reasonable micro-grid operation may benefit the voltage recover to avoid the large scale loss of load.