A Simple Overcurrent Scheme for Distribution Networks with High Penetration of Inverter-Based Generators

The number of inverter-based generators (IBGs) connected to electrical networks has increased significantly over the past two decades. Some IBGs are connected to the distribution networks close to customers to minimize transmission losses. IBGs can be designed to operate in grid-connected and islanding modes to improve the continuity of the power supply. The fault current contribution of conventional generators reaches more than eight p.u. while the fault current of IBGs is limited to less than twice the rated current. The change in the system configuration from grid-connected operation to islanding operation creates different system fault current magnitude. Accordingly, the setting of conventional overcurrent protection to detect faults during both operating modes is a real technical challenge. The paper proposes a simple and economic overcurrent protection scheme with two different settings groups to detect electrical faults in distribution networks with high IBGs penetration. The instantaneous overcurrent function is included in the proposed scheme to automatically select the required overcurrent settings group based on the fault current of the operating mode. The impact of the fault current variation on conventional overcurrent protection and the proposed scheme effectiveness were demonstrated on a modified IEEE 13-bus distribution system using the MATLAB/SIMULINK software.