Micro-grid Relay Protection Settings Adaptation
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Solution Overview
Problem
The existing systems for micro-grids face challenges in distinguishing between normal and fault currents when transitioning between grid-connected and islanded states, leading to inadequate protection during transitions due to the difference in fault current magnitudes and power system characteristics.
Innovation Solution
A system and method that staggers the switching of protection settings groups for relays in a micro-grid, where a switch relay sends a signal to a controller to change the settings group of power source and load relays before disconnecting from or reconnecting to the utility grid, ensuring continuous protection during transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the fault current detectors in the micro-grid are set for detecting a fault current well above the normal current levels of the utility grid, then they can detect faults when the micro-grid is grid-connected, but they may not detect a lower fault current when the micro-grid is islanded
Solution Approach 1:
The relay protection settings are made dynamic by automatically switching between grid-connected settings group and islanded settings group based on the operational state of the micro-grid. This allows the detection thresholds to adapt in real-time: using higher thresholds when grid-connected and lower thresholds when islanded, thereby resolving the contradiction between detecting high fault currents in utility mode and low fault currents in islanded mode.
Solution Approach 2:
The invention changes the detection parameters (fault current thresholds) based on the micro-grid's operational state. By switching between two distinct settings groups with different parameter values, the system maintains high measurement precision for both grid-connected and islanded conditions without requiring a single fixed threshold that would compromise detection capability in either state.
2Measurement precision
If the fault current detectors in the micro-grid are set for detecting a fault current typical of fault currents when the micro-grid is islanded, then they can detect faults when the micro-grid is islanded, but they may detect a fault current that is a normal current when the micro-grid is grid-connected
Solution Approach 1:
The relay automatically adjusts its detection characteristics dynamically based on the micro-grid's operational state. When grid-connected, the system uses settings group configured for higher fault current thresholds, preventing false detection of normal utility-sourced currents. When islanded, it switches to settings group with lower thresholds appropriate for micro-grid generator fault currents, thereby maintaining detection accuracy while avoiding false positives in either state.
Solution Approach 2:
The invention implements parameter changes by switching between two distinct settings groups with different detection thresholds. The grid-connected settings group uses higher current thresholds to avoid false detection of normal utility currents, while the islanded settings group uses lower thresholds to detect micro-grid generator fault currents, thus resolving the contradiction between detection sensitivity and false positive rate.
3Ease of operation
If all relays in the micro-grid switch settings groups simultaneously during transition, then the transition is simple to control, but there is a period where the relay cannot adequately protect the micro-grid components
Solution Approach 1:
The invention segments the relay settings group switching process by implementing a staggered transition approach. Different relays (power source relays and load relays) switch settings groups at different times during the micro-grid transition. This segmentation ensures that at least some relays maintain appropriate protection settings throughout the transition period, preventing a complete protection gap while still allowing automated control of the overall transition process.
Data Source
AI summary
A system and method for changing protection settings groups for relays in a micro-grid between a grid-connected settings group and an islanded settings group. The method changes a power source relay from the grid-connected settings group to the islanded settings group before the micro-grid is disconnected from the utility grid, disconnects the micro-grid from the utility grid, and then changes a load relay from the grid-connected settings group to the islanded settings group after the micro-grid is disconnected from the utility grid. The method also changes the load relay from the islanded settings group to the grid-connected settings group before the micro-grid is connected to the utility grid, connects the micro-grid to the utility grid, and then changes the power source relay from the islanded settings group to the grid-connected settings group after the micro-grid is connected to the utility grid.