Protective Relay Logic for Single-Phase Microgrid Islanding
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Solution Overview
Problem
Customers at the end of long distribution feeders experience frequent and prolonged outages due to upstream faults, with no cost-effective solutions available for improving reliability using traditional methods, as they lack nearby distribution lines, neighboring utilities, or transmission lines for transfers.
Innovation Solution
Implementing a protective relay control scheme that automatically isolates the grid, commands a Battery Electric Storage System (BESS) to form a microgrid, and synchronizes with the grid to restore service, or trips the BESS if synchronization fails, ensuring seamless restoration to normal grid supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional poles-and-wires methods are used to improve reliability, then infrastructure can be expanded, but cost becomes prohibitive in remote locations
Solution Approach 1:
The system segments the distribution system into isolated microgrid zones that can operate independently. The single-phase recloser is divided into control modules that can detect faults and coordinate isolation/synchronization operations, allowing remote taps to form self-sufficient microgrids without requiring extensive additional infrastructure.
Solution Approach 2:
A BESS (Battery Energy Storage System) acts as an intermediary energy source between the utility grid and remote customers. The BESS provides power during outages and enables microgrid formation, serving as a bridge that eliminates the need for costly traditional infrastructure extensions to remote locations.
2Loss of time
If automatic microgrid formation is implemented, then outage duration is reduced, but control system complexity increases
Solution Approach 1:
The recloser is pre-configured with control logic and communication capabilities before outages occur. During normal operation, the system continuously monitors grid status and pre-coordinates with the BESS, enabling immediate microgrid formation when outages happen without requiring complex real-time decision-making during the event.
Solution Approach 2:
The system implements continuous feedback loops where the recloser monitors grid voltage, frequency, and power flow, and automatically adjusts BESS charging/discharging operations. This feedback mechanism simplifies control by using real-time measurements to automatically maintain microgrid stability without complex manual intervention.
3Object-affected harmful factors
If safety checks are performed at all steps, then operator safety is ensured, but operational time increases
Solution Approach 1:
The system performs safety checks and isolates the microgrid from the utility grid before BESS discharging begins. The recloser opens isolation switches and verifies zero energy conditions in advance, ensuring operator safety is established before restoration operations commence, thereby preventing accidents without delaying the overall restoration timeline.
Data Source
AI summary
A system for improving grid reliability in remote or isolated locations includes a battery tripping module, the battery tripping module determining whether a microgrid zone may be formed upon a fault. The system further includes a microgrid formation module, the microgrid formation module forming a microgrid zone, the microgrid zone connected to a BESS (battery electric storage system), the BESS providing power to the microgrid.