DC Insulation Monitoring Circuit for Neutral-to-Earth Fault Detection
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Solution Overview
Problem
Conventional insulation resistance monitor devices for bipolar DC power systems are complex and costly, and they fail to measure insulation resistance between the neutral line and the protective earth, which is crucial for safety in systems without a neutral line.
Innovation Solution
A DC power system with a positive line, neutral line, negative line, and protective earthing terminal, equipped with a first resistor, sensing resistor, and detection circuit to measure insulation resistance between these lines and the earthing terminal, using sensing voltage to detect abnormalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional insulation resistance monitor devices use multiple resistors and switches to measure insulation resistance, then the measurement capability is provided, but the device complexity and cost increase
Solution Approach 1:
The patent merges the functions of multiple resistors and switches into a single integrated monitoring device that uses a microcontroller to control measurement switching and process data. This consolidation reduces the number of discrete components while maintaining the ability to measure insulation resistance between multiple lines and protective earth, thereby reducing device complexity and cost.
Solution Approach 2:
The monitoring device is designed to universally measure insulation resistance between any combination of positive line, neutral line, negative line, and protective earth. A single device performs multiple measurement functions that would traditionally require separate dedicated circuits for each measurement, achieving multi-functionality without proportionally increasing complexity.
2Adaptability or versatility
If conventional insulation resistance monitor devices are designed for DC power systems with only one DC source, then the measurement for such systems is provided, but the ability to measure insulation resistance between neutral line and protective earth is lost
Solution Approach 1:
The monitoring device is designed with universal adaptability to work in DC power systems regardless of whether they have one or two DC sources. The device can measure insulation resistance between any line (positive, neutral, negative) and protective earth, making it versatile for different system configurations while maintaining measurement capability for the neutral line to protective earth, which was previously unavailable in conventional single-source designs.
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
The system accurately detects and distinguishes insulation degradation or failure between the protective earth and any of the positive, neutral, or negative lines, enhancing safety and reducing complexity and cost.
Implementation Method 1
The first detection circuit is electrically connected to the first and second terminals of the first sensing resistor, and is configured to measure a sensing voltage across the first sensing resistor and detect whether an insulation resistance between the protective earthing terminal and any of the positive line, the neutral line and the negative line is abnormal according to the sensing voltage
Data Source
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Figure 3A
AI summary
A DC power system (1a, 1b, 1c, 1d, 1e, 1f) and an insulation resistance monitor device (14) thereof are provided. The DC power system (1a, 1b, 1c, 1d, 1e, 1f) includes positive, neutral and negative lines (11, 12, 13), a protective earthing terminal (PE) and a grounding resistor (Rgnd). The grounding resistor (Rgnd) is electrically connected between the neutral line (12) and the protective earthing terminal (PE). The insulation resistance monitor device (14) includes a first resistor (R1), a first sensing resistor (Rs) and a first detection circuit (141). The first resistor (R1) is coupled to the positive or negative line (11, 13). The first sensing resistor (R1) is coupled between a second terminal of the first resistor (R1) and the protective earthing terminal (PE). The first detection circuit (141) is electrically connected to the first sensing resistor (Rs), and is configured to measure a sensing voltage across the first sensing resistor (Rs) and detect whether an insulation resistance between the protective earthing terminal (PE) and any of the positive, neutral and negative lines (11, 12, 13) is abnormal according to the sensing voltage.