Ground-Fault Threshold Calibration Using a Self-Injection Circuit
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Solution Overview
Problem
Conventional systems for ground-fault threshold calibration are bulky, costly, and require externally calibrated equipment, making them inefficient and resource-intensive.
Innovation Solution
A self-injection circuit and auto-monitoring system that uses existing circuit elements to calibrate ground-fault thresholds without external equipment, employing a self-injection of a half-cycle AC through the current transformer, measuring output voltage, and converting it to a digital value to determine a tolerance level for ground-fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ground-fault threshold calibration systems are used, then calibration can be performed, but the systems are bulky, costly, and require externally calibrated equipment
Solution Approach 1:
The system performs self-calibration using its own internal circuitry. The microcontroller generates a self-test signal that is injected into the current transformer, and the system measures its own response to determine calibration factors without requiring external calibration equipment.
Solution Approach 2:
The invention extracts and eliminates the dependency on external calibrated equipment (voltage sources, current sources) by implementing an internal self-test circuit that generates its own calibration signals and measures its own response, thereby removing the need for bulky external devices.
2Measurement precision
If conventional calibration equipment is used, then ground-fault threshold can be calibrated, but resource consumption and cost increase
Solution Approach 1:
The microcontroller serves multiple functions: it controls normal circuit operation, generates self-test signals, measures calibration responses, and calculates calibration factors. This multi-functionality eliminates the need for dedicated external calibration equipment, reducing resource consumption while maintaining measurement precision.
Solution Approach 2:
The calibration function is merged with the normal operation circuitry. The self-test signal generation, current transformation, voltage measurement, and calibration calculation are all integrated into the existing microcontroller-based system, eliminating the need for separate external calibration devices.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate and efficient ground-fault threshold calibration, reducing resource consumption and cost, while accounting for variations in current transformer output, thereby improving reliability and consistency in ground-fault detection.
Implementation Method 1
The self-injection circuit generates a half-cycle AC trigger pulse. The trigger pulse is applied at regular time intervals to a primary of the current transformer.
Implementation Method 2
measure, using the rectified voltage detection circuit, a rectified voltage, wherein the rectified voltage is based on an AC voltage powering the circuit board
Implementation Method 3
convert the expected current to a digital value using an analog to digital converter
Data Source
AI summary
A system for calibrating ground fault threshold using auto-monitoring circuit, the system is provided. The system includes a circuit board comprising a self-injection circuit, a rectified voltage detection circuit, and a controller. The controller is configured to provide, using the self-injection circuit, a trigger pulse as input to the self-injection circuit. The rectified voltage detection circuit is used to measure a rectified voltage from the current transformer, where the rectified voltage is based on an AC voltage powering the circuit board. Based on the rectified voltage a series resistor in a current path, an expected current through the current transformer is determined. The expected current is converted to a digital value using an analog to digital converter. A tolerance level of the current transformer is determined based on the digital value.