Adaptive Distance Protection Principle for Distribution Lines with T-Connected Inverter-Interfaced Distributed Generators
The proliferation of inverter-interfaced distributed generators (IIDGs) connected via T-taps in distribution networks degrades the reliability of conventional distance protection, causing maloperation or failure due to the low-voltage ride-through (LVRT) control strategy that dynamically adjusts IIDG output currents. This paper analyzes the fault output characteristics of IIDGs and the resulting impedance measurement errors in traditional distance protection. Based on fault equivalent networks, the evolution of electrical quantities in IIDG-T-connected distribution lines is derived. A complete adaptive distance protection scheme is proposed for three-phase and two-phase short-circuit faults. The scheme iteratively solves the IIDG short-circuit current using only local measurements, computes an adaptive setting coefficient, and dynamically updates the distance protection setting every 5 minutes. Simulation results on PSCAD/EMTDC demonstrate that the proposed scheme is immune to IIDG-T capacity, output fluctuations, fault location, and fault type. It eliminates the need for communication infrastructure, reduces costs, and maintains high reliability under solar irradiance variations, overcoming the limitations of prediction-based methods that suffer from large errors when irradiance deviates from forecast samples.