Active Conductor Interruption Detection in Unearthed DC Systems
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Solution Overview
Problem
In ungrounded DC voltage power supply systems, direct contact with two active conductors poses a significant risk of electric shock, which existing safety measures, such as residual current devices, cannot reliably detect, and alternative safety methods like SELV or PELV are not feasible due to energy and material efficiency requirements.
Innovation Solution
Implementing methods that include connecting a resistive minimum load to generate a minimum load current, determining if the current falls below a threshold, and signaling a drop in current to indicate an active conductor interruption, or using high-impedance resistors between active conductors and earth to monitor insulation resistance or residual voltage, and switching off the power supply if safety limits are exceeded.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an ungrounded DC power supply system is used to ensure operational safety and continuous power supply, then fire safety and contact safety are improved, but the risk of electric shock from direct contact with two live conductors increases
Solution Approach 1:
The patent applies preliminary action by continuously monitoring the current in the DC power supply system before a fault can develop. The monitoring device detects interruptions or abnormal current conditions proactively, allowing the system to maintain safe operation and prevent electric shock hazards before they can affect users.
Solution Approach 2:
The patent implements feedback through a monitoring device that continuously measures current flow and provides real-time information about system status. This feedback mechanism enables the system to detect conductor interruptions or abnormal conditions and respond appropriately, maintaining both continuous power supply and safety.
2Difficulty of detecting and measuring
If residual current devices are used to detect faults, then fault detection capability is improved, but they cannot reliably detect direct contact with two active conductors in DC IT systems
Solution Approach 1:
The patent replaces the traditional residual current device mechanism with a monitoring device specifically designed for DC IT systems. Instead of relying on residual current measurement that fails in two-conductor contact scenarios, the system uses direct current monitoring that can detect any abnormal current condition, including simultaneous contact with both active conductors.
Solution Approach 2:
The patent changes the detection parameter from residual current (which is zero in two-conductor contact) to direct current monitoring. By monitoring the actual current flow through the conductors and detecting interruptions or abnormal patterns, the system achieves reliable detection of all fault types including two-conductor contact.
3Object-affected harmful factors
If protective measures like SELV or PELV are implemented, then electric shock protection is improved, but energy and material efficiency requirements cannot be met
Solution Approach 1:
The patent introduces a monitoring device as an intermediary between the DC power supply system and the load. This intermediary continuously assesses system safety through current monitoring and can disconnect or alert when hazards are detected, providing protection equivalent to SELV/PELV without requiring voltage reduction or additional protective infrastructure that would compromise energy efficiency.
Data Source
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AI summary
The invention relates to a method for detecting a break in a live conductor in an ungrounded DC power supply system. Five alternative methods are presented, each based on determining a current load current, a current total insulation resistance, a current displacement voltage, a current total capacitance, or a current total impedance. Each of these methods minimizes the hazard of accidental contact between two live conductors in an ungrounded DC power supply system.