Impact analysis of flexible interconnection devices in distribution networks and a setting calculation method for overcurrent protection scheme

The integration of flexible interconnection devices (FIDs) into distribution networks introduces complexities in power flow management under both normal and transient/fault conditions, thereby decreasing the selectivity, sensitivity, and reliability of common current protection schemes. This article examines the impact of FIDs on existing current protection arrangements and proposes a novel method for recalculating the overcurrent protection setting. The AC output characteristics of the FID for a short period after AC fault occurrence are first investigated. It is followed by an analysis of FID's impact on the three-stage current protection scheme in flexible interconnected distribution networks, conducted through theoretical calculations in MATLAB and simulations in PSCAD/EMTDC. A quantitative assessment of the mal-operation and non-operation of current protection caused by FIDs of varying capacities, power flow directions, and locations, with a focus on the typical 10 kV 10MVA FID, is also performed. Based on the above findings, a calculation and modification method for Stage III overcurrent protection setting is presented to address mal-operation issues in FID-based distribution networks, with its feasibility validated through electromagnetic transient simulations.