An Adaptive and Scalable Protection Coordination System of Overcurrent Relays in Distributed-Generator-Integrated Distribution Networks  
[PERSON]  
1 Department of Electrical and Computer Engineering (ECE), Faculty of Engineering, Vietnamese-German University (VGU), Thu Dau Mot City 7  
decrease in fault-currents contributed from the utility, which can reduce the sensitivity and selectivity of OCRs on feeders of the distribution network [4; 5; 6; 7; 8]. Malfunction issues of OCRs in the DG-integrated DN could be over-reach or under-reach of OC relays, loss of sensitivity/selectivity, blinding of overcurrent protection, false tripping or sympathetic tripping of overcurrent protection [9]. Several studies are performed on protection coordination of overcurrent relays in a DG-integrated DN. In [10], risks of protection miscoordination of OCRs or reclosers are indicated in each fault isolation and service restoration (FISR) plan when the DN needs to change its topology due to faulted events. In [11], the authors point out that the allowable fault-current contribution of IBDGs can significantly impact a DN's overcurrent protection system. In [12; 13; 14; 15], the threshold setting of OCRs is only valid for typical DG capacities. In [16], the authors have introduced a hybrid PSO-based protection coordination method to adjust TDS parameters of directional overcurrent relays. The paper [17] proposed an optimization function to calculate tripping and pick-up thresholds of OCRs in a range of pre-defined values. In [18], an adaptive overcurrent protection system is developed for fault detection and isolation in a DG-penetrated distribution network. The research paper [19] has proposed an ANN-based method to divide a distribution network into multiple zones, and then an overcurrent protection scheme for each zone is developed. In [20], an effective overcurrent protection system is developed to protect a distribution network when considering two on-grid and off-grid operation modes of DGs. From the above references, it could be generally concluded that the accurate calculation of fault-current values can strongly impact the protection coordination results of OCRs on a DN having DGs. That assumption could be more considered in this study by contributing a novel proposal to determine the min-max confidence interval of fault currents according to each different fault type. The estimated confidence interval of fault currents will then be the basis for properly selecting tripping and pick-up thresholds of the OCRs in the DN. The DG-integrated distribution networks mostly use digital relays with overcurrent and sequence-component-based protection functions. Accordingly, overcurrent-based protection functions, e.g., 50, 51, 67, or sequence-component-based protection functions, e.g., 46, 47, 50 REF, 46 BC, 3l0, 3V0, can be properly re-adjusted when the topology of DN is changed under fault events. As presented in [18], a low-voltage microgrid (LVMG) protection system using directional overcurrent protection functions in digital relays is developed along with its coordination strategies. The paper [21] presents a protection coordination solution based on symmetrical and differential current components to detect faults in a grid-connected microgrid. In [22], the authors propose a definite-time overcurrent protection model regarding the placement of DGs in a distribution network. In [23], a novel protection coordination algorithm is developed to improve the selectivity of the protection system through using a three-level communication network, directional overcurrent protection functions, and under/overvoltage-based protection functions, which are available in digital relays. On the other hand, references [24; 25] have considered sequence-component-based protection functions, e.g., positive-, negative-, zero-sequence components, along with a GOOSE (Generic Object Oriented System Event) solution for detecting, classifying and isolating symmetrical and asymmetric faults in microgrids or DG-penetrated distribution networks.