Common-Mode Current Fault Detection in High-Impedance DC Feeders
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Solution Overview
Problem
Traditional current-based fault detection methods are no longer viable for high voltage DC systems with a rectifier midpoint high impedance ground, as they result in significantly reduced fault current levels, necessitating new methods for fault isolation and detection.
Innovation Solution
A system utilizing current sensors to detect net common mode current in DC feeders and AC feeders, with a controller determining fault location based on common mode current thresholds and phase angle, enabling isolation of faults in specific feeders or distribution loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a rectifier midpoint high impedance ground is used in high voltage DC systems, then fault current levels are significantly reduced and equipment damage is mitigated, but traditional current-based fault detection methods are no longer viable
Solution Approach 1:
The patent changes the detection parameter from fault current magnitude to common mode current characteristics. By monitoring the common mode current and its phase angle relationship with AC feeders, the system can detect faults even when fault current levels are reduced by the high impedance ground configuration.
Solution Approach 2:
The patent introduces common mode current as an intermediary measurement parameter. Instead of directly measuring fault current through traditional methods, the system uses common mode current sensors to detect the presence and characteristics of faults, which then inform the control system about fault conditions.
2Measurement precision
If traditional generator neutral grounding is used, then adequate current sourcing levels are available for fault detection, but aircraft weight increases and fault current levels are too high causing equipment damage
Solution Approach 1:
The patent replaces traditional current-based detection mechanisms with a new detection approach based on common mode current monitoring and phase angle analysis. This substitution enables sensitive fault detection without requiring high fault current levels, thus avoiding equipment damage while maintaining detection capability.
Solution Approach 2:
The common mode current monitoring system serves multiple functions: it detects faults in both AC and DC feeders, identifies fault locations through phase angle analysis, and works with the high impedance ground configuration. This multi-functional approach replaces multiple separate detection systems that would be needed with traditional grounding.
Data Source
AI summary
A system includes a generator. Three AC feeders are connected for feeding AC output from the generator. A rectifier is electrically connected to the three AC feeders and to a load via a first DC feeder and a second DC feeder. A first resistor connects between a the first DC feeder and ground. A second resistor connects between the second DC feeder and ground. At least one of a first current sensor is operatively connected to detect current in the first DC feeder and/or a second current sensor is operatively connected to detect current in the second DC feeder. A controller is configured to monitor for changes in common mode current based on the input from the at least one current sensor, and to determine presence of a fault if change in the common mode current exceeds a predetermined threshold.