Earth-Fault Protection Using Time-Based Body Current Estimation
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Solution Overview
Problem
Existing earth-fault protection systems fail to operate accurately and/or fast enough, posing a risk to personal safety in three-phase electric networks.
Innovation Solution
Determine an estimate of body current resulting from a detected phase-to-earth fault in a three-phase electric network based on the estimate of the earth-fault current and operate the earth-fault protection based on predetermined permissible body current values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If earth-fault protection operates based on fault current magnitude with predetermined operate time, then the protection system can detect and eliminate faults, but the operation may not be accurate or fast enough to ensure personal safety
Solution Approach 1:
The patent changes the parameter basis for protection operation from fault current magnitude alone to estimated body current magnitude. By calculating the actual body current that a person would receive during a fault (considering fault current, earth fault impedance, and body impedance), the system achieves more accurate and safety-critical protection decisions, enabling faster and more reliable operation.
2Adaptability or versatility
If earth-fault protection uses inverse time characteristic with threshold values, then the protection can adapt to different fault conditions, but it fails to accurately assess personal safety risk
Solution Approach 1:
The patent introduces an intermediary calculation step that estimates body current based on fault current and impedance values. This intermediary parameter (estimated body current) serves as a more direct measure of personal safety risk than fault current alone, enabling the protection system to accurately assess whether the fault poses a danger to human life while maintaining adaptability to different fault conditions.
Data Source
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AI summary
A method and apparatus for earth-fault protection in a three-phase electric network, the apparatus being configured to detect (100) a phase-to-earth fault in the three-phase electric network, determine (110) an estimate of an earth-fault current of the detected phase-to-earth fault, determine (130) an estimate of a body current as a function of time resulting from the detected phase-to-earth fault on the basis of the determined estimate of the earth-fault current and an elapsed time from the detecting of the phase-to-earth fault, compare (140) the determined estimate of the body current to a predetermined threshold for the body current defined as a function of time and operate (150) the earth-fault protection in the three-phase electric network in response to the determined estimate of the body current exceeding the predetermined threshold for the body current.