Current Transformer Secondary Disconnection Detection Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current transformers (CTs) face a critical safety issue as the secondary side must remain connected to a load; if disconnected, the primary side current can cause hazardous high voltage, necessitating a method to detect disconnection.
Innovation Solution
A circuit and method involving a sampling circuit, a pull-up circuit, and a processor to monitor and determine the connection status of the secondary side by sampling signals, storing calibration data, and using a detector to assess signal information during a diagnostic phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the secondary side of the current transformer is left open for measurement, then the CT can generate proportional current for safe measurement, but if the secondary side is disconnected, the primary side current will push the secondary voltage to extremely high values which is harmful and dangerous
Solution Approach 1:
The patent implements a monitoring system that continuously samples the secondary side voltage and compares it against reference values stored in memory. The processor receives sampled signals, determines whether the CT is in measurement or diagnostic mode, and generates alerts when disconnection is detected. This feedback mechanism enables real-time detection of secondary side disconnection conditions, allowing the system to respond before hazardous voltage levels develop.
Solution Approach 2:
The patent introduces a pull-up circuit as an intermediary component that is switchably coupled to the secondary side. During diagnostic mode, the pull-up circuit is activated to create a controlled load on the secondary side, preventing voltage buildup in case of disconnection. This intermediary circuit acts as a protective measure that can be engaged when measurement is not actively being performed.
2Reliability
If the secondary side must remain connected to prevent hazardous voltage, then safety is improved, but the ability to perform accurate measurement and diagnostics is limited
Solution Approach 1:
The patent implements dynamic switching between measurement mode and diagnostic mode. The system can transition between these modes based on operational requirements. During measurement mode, the secondary side remains connected for normal operation. During diagnostic mode, the system switches to activate the pull-up circuit and perform disconnection detection tests. This dynamic approach allows the system to optimize for either measurement accuracy or safety diagnostics at different times.
Solution Approach 2:
The patent employs periodic diagnostic phases where the system temporarily switches to diagnostic mode to check for secondary side disconnection. During these periodic intervals, the pull-up circuit is activated and voltage sampling is performed to detect potential issues. This periodic action allows the system to maintain normal measurement operations most of the time while periodically verifying safety conditions, thus balancing measurement capability with safety monitoring.
3Reliability
If voltage sampling is performed to detect disconnection, then safety monitoring is improved, but the system complexity increases due to additional circuits and processing requirements
Solution Approach 1:
The patent designs the voltage sampling circuit to serve multiple functions. The same sampling circuit is used both during normal measurement operations to capture secondary side voltage for measurement purposes and during diagnostic operations to detect disconnection conditions. The processor similarly handles both measurement data processing and diagnostic evaluation. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in system complexity.
Solution Approach 2:
The system uses its existing measurement infrastructure to perform safety diagnostics. The processor that already exists for measurement purposes is utilized to evaluate diagnostic data. The memory structure is designed to store both measurement reference values and diagnostic threshold values, allowing the system to self-verify its own operational status without requiring external monitoring equipment. This self-service approach minimizes additional complexity.
Data Source
AI summary
An apparatus for detecting disconnection of a secondary side of a current transformer includes a sampling circuit coupled to the secondary side of the current transformer that samples signals from the secondary side of the current transformer. A pull-up circuit is switchably coupled to the sampling circuit in response to a coupling signal in a diagnostic phase. A processor is coupled to the sampling circuit for receiving sampled signals from the sampling circuit. The processor extracts corresponding signal information from the sampled signals and stores the extracted signal information in a memory. The extracted signal information corresponds to statuses that the secondary side of the current transformer is connected or disconnected to a load. A detector is coupled to the processor and the memory, and accesses the memory using the signal information of the sampled signals.