The increasing integration of inverter-based solar photovoltaic (PV) generation into medium-voltage (MV) distribution networks has introduced significant protection coordination challenges. Traditional overcurrent protection schemes, originally designed for radial feeders with unidirectional power flow and predictable fault current levels, become ineffective due to the limited and controlled fault current contribution of PV systems, leading to relay blinding, mis-coordination, nuisance tripping, and delayed fault clearing. This paper presents the modelling and simulation of an adaptive protection scheme for 11 kV and 33 kV distribution feeders with integrated solar PV, modelled after the ZESCO Limited network in Zambia. Detailed system models were developed using MATLAB/ Simulink, SolidWorks, and Power World Simulator to evaluate fault behaviour under varying solar penetration levels. An adaptive protection algorithm dynamically adjusts relay settings, including pickup current and time multiplier setting (TMS), based on real-time system conditions such as load variation, fault levels, and PV output. Simulation results demonstrate that the proposed scheme improves relay coordination, reduces fault clearing time, and enhances system reliability compared to conventional fixed-setting protection methods. The study confirms that adaptive protection is a practical and essential solution for enabling higher solar penetration in Zambian distribution networks.

Full text: IJEIR_2998_FINAL.pdf