Protection solutions and their performance assessment for MV embedded microgrid networks

Numerous innovative protection schemes involving a combination of overcurrent relays (OCRs) and directional overcurrent relays (DOCRs) have been investigated for a distribution network with distributed generators (DGs) and microgrids (MGs) governed by existing anti-islanding regulations. However, the protection solutions for the embedded microgrids (EMGs) have not been thoroughly investigated, where conventional overcurrent and islanding protection implemented at a single point-of-common-coupling (PCC) proves inadequate. The analysis in this paper shows that EMG supply reliability can deteriorate by up to 34% more than that of the distribution network itself. To address this issue, this paper proposes a suite of protection solutions designed for future embedded networks, aiming to minimize supply disruption through isolation of faulty network segments and maintaining supply to the rest of the network from the grid and EMG. The proposed protection solutions involve the addition of new DOCRs and their coordination among themselves and with the existing conventional OCRs to ensure adequate protection. A simple framework employing two strategies, based on feeders’ radial distance and connected load power is proposed for the placement of additional DOCRs, resulting in numerous solution scenarios (SSs) with different combinations of OCR and DOCRs. A comprehensive techno-economic performance analysis is conducted by estimating the improvement in reliability indices, the associated cost savings, and the deployment cost of each SS to determine its economic viability. The findings reveal that the most cost-effective solution have enhanced system reliability by up to 67%, demonstrating that the proposed simple-yet practical framework provides highly effective and viable protection solutions for EMGs.