Ultra-fast FLISR in practice

Fault location, isolation, and service restoration (FLISR) have evolved from manual processes to automated systems through the introduction of remote-controlled switching and advanced communication networks. Automated FLISR enhances grid reliability by minimizing stress on primary equipment and ensuring high service availability. Traditional implementations rely on centralized systems, where decision-making typically is semi-automated and dependent on communication networks. A fully distributed FLISR system leverages adjacent devices in open-loop and radial configurations to autonomously identify and isolate faults and restore power. By eliminating centralized decision-making, such systems are capable to reduce restoration time and improve overall system availability. Accurate and cost-effective fault detection in the distribution network is crucial for a commercial success. This paper introduces a fault detection approach capable of reliably identifying high-ohmic earth faults using only three phase current measurements without requiring zero sequence current or polarizing voltage. This method provides sensitive and robust fault detection suitable for secondary substations, forming the foundation for dependable and ultra-fast FLISR. This paper presents data and experiences from commercial installations of distributed FLISR, including primary earth fault tests in open-loop configurations with both circuit breakers and load disconnector switches. Optimization strategies for distributed FLISR are discussed, addressing network characteristics and communication capabilities.