# Wide-Area Protection System for Radial Smart Distribution Networks
## 1 Introduction  
The integration of Distributed Energy Resources (DERs) has gained attention and popularity in modern energy-efficient electricity distribution networks. Despite the valuable advantages of DERs in distribution networks, they can be a great challenge for the safe and reliable operation of power distribution systems. Safe operation of distribution networks is directly dependent on the accurate and reliable operation of protection systems. The presence of DERs in distribution networks introduces dynamic bidirectional fault currents that can be challenging for the detection and accurate location of faults, specifically for traditional overcurrent schemes. To overcome these challenges, numerous protection schemes are proposed in the literature. The proposed methods are either dependent on data transmission systems or independent from any communication system. The methods using communication systems can be further classified into hierarchical methods and horizontal methods. In hierarchical methods, a Central Processing Unit (CPU) manages coordination between relays by updating relay settings [1, 2] or monitoring network signals and issuing trip commands for fault isolation [3]. Horizontal methods involve distributed data processing units that utilize data transmission between relays [4, 5] or agents [6, 7]. The approaches independent of data transmission networks can be classified into standard overcurrent formulations and heuristic formulations for fault detection and location. Standard overcurrent schemes account for various network operating modes and configurations, utilizing optimization techniques to coordinate relays for accurate fault determination [8, 9, 10, 11]. Heuristic methods which employ non-standard functions for fault detection, incorporating a mixture of voltage [12] and/or current measurements, in addition to data mining based methods, are also suggested for fault diagnosis applications [13]. Wide-area protection serves as an effective tool within smart grids, primarily utilized for monitoring and management purposes. In recent years, these systems have also found application in protection strategies for smart grids, offering flexibility in addressingthe challenges posed by the integration of DERs. In [14], a differential-based wide-area protection system is proposed for meshed networks which is capable of detecting both high-impedance and low-impedance faults. Reference [15] proposes a method for the detection of high-impedance faults in radial networks using the phase difference of the network relays. A method focusing on modeling the non-recursive phasor estimation method aiming to accurately detect fault zones by analyzing positive-sequence voltage measurements before and after faults is presented in [16] for power transmission networks. A reliability modeling and assessment method is proposed in [17] for wide-area protection systems, considering the decision accuracy of protection algorithms and tripping reliability of protection devices to form the operation accuracy of wide-area protection systems. Ref. [18] introduces a dynamic approach to wide-area cooperative protection, employing cooperative control of distributed multi-agent systems and graph theoretical techniques to oversee the cooperation of each agent within designated protection areas and adjust to changing power system configurations. Simultaneous optimization of partitioning and optical communication link placement in wide-area protection systems is presented in [19] to minimize construction costs while ensuring reliable and real-time data transmission. Ref. [20] proposes a new integrated backup protection algorithm for distance relay based on wide-area measurements to address challenges in conventional protection caused by stressed power system conditions and the presence of offshore wind farms. While most of the wide-area protection systems are designed for power transmission networks, there are some approaches that developed wide-area systems for the protection of smart distribution networks.