Advanced Relaying for DG-Penetrated Distribution System

The proliferation of renewable-based distributed generators poses protection challenges for the overcurrent relays due to the intermittent nature and control schemes. Converters present in the AC side restrict the fault current up to two per unit. Therefore, the overcurrent relay present in the AC microgrid maloperates during the fault. The proposed technique is based on the corresponding sum of the current samples obtained after every half-cycle (Ts/2), computed for each phase, and utilized to derive an index to detect the fault. The index thus derived is robust to noises, load variations, and other transients in the system. However, the technique requires removing transients and other noises before comparing the threshold for fault detection, which is resolved using the fast Fourier transform (FFT). Further, the magnitude of decaying DC (as another index) present in the signal is calculated using the least square technique for detecting the three-phase fault. The proposed algorithm is tested on an IEEE 14-bus system and a Real-Time Digital Simulator microgrid model. The fault detection technique is accurate for different faults under different operating conditions like noise, CT saturation, sudden load change, etc.