Insulation Resistance Measurement Under Line Voltage Fluctuations
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Solution Overview
Problem
Existing methods for determining insulation resistance and leakage capacitance in ungrounded power supply systems are time-consuming and prone to interference from low-frequency line voltage changes, particularly in AC and DC systems, making accurate and rapid measurements challenging.
Innovation Solution
A method utilizing unipolar or bipolar coupling of a measuring voltage with a measured resistance, combined with recursive QR decomposition of a linear difference equation, allows for continuous measurement of insulation resistance and leakage capacitance, minimizing the need for filtering and reducing computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional active insulation monitoring methods are used with square-shaped measuring voltage pulses, then insulation resistance can be determined, but the measurement takes several minutes for larger leakage capacitances due to settling time requirements
Solution Approach 1:
The patent applies sinusoidal measuring voltage at line frequency instead of static square pulses, enabling dynamic continuous measurement. The sinusoidal excitation allows determination of insulation resistance and leakage capacitance during the ongoing AC cycle without requiring the system to settle, thus reducing measurement time from several minutes to continuous real-time monitoring.
Solution Approach 2:
The patent changes the measuring voltage from DC square pulses to AC sinusoidal voltage at line frequency. This parameter change enables the use of frequency-domain analysis and Fourier transformation to separate the measuring voltage response from line voltage variations, allowing rapid determination of insulation parameters without settling time.
2Reliability
If low-frequency line voltage changes are filtered out to enable measurement, then measurement interference is reduced, but the filtering process is complex and may still not fully eliminate interference effects
Solution Approach 1:
The patent uses periodic sinusoidal measuring voltage at line frequency that synchronizes with the power grid frequency. By locking onto this known periodic frequency, the measurement system can naturally reject other frequency components including low-frequency line voltage variations, eliminating the need for complex low-pass filters while maintaining measurement reliability.
Solution Approach 2:
The patent replaces physical analog filtering mechanisms with digital signal processing techniques. By using Fourier transformation and frequency-domain analysis on the measured voltage and current signals, the system can selectively extract the sinusoidal measuring voltage components and reject other frequency components, substituting complex hardware filtering with computationally efficient digital methods.
3Loss of time
If matrix inversion is used to determine model parameters for predicting settling, then insulation resistance can be identified before voltage settles, but the computational complexity and time required for matrix inversion remains high
Solution Approach 1:
The patent replaces complex iterative mathematical optimization methods (matrix inversion for model parameter adaptation) with direct frequency-domain calculation using Fourier transformation. The sinusoidal excitation allows direct computation of insulation resistance and leakage capacitance from the amplitude and phase of the measured voltage and current at the excitation frequency, eliminating the need for iterative settling prediction and reducing computational complexity.
Data Source
AI summary
A method for determining an insulation resistance and a discharge capacitance to earth of an unearthed DC power supply system, wherein a linear differential equation is implemented with a measured voltage as a function of the measurement voltage and the grid voltage and with grid parameters formed from the shunts (RM), from the insulation resistances to be determined and from the discharge capacitances to be determined. N linear differential equations are used to implement a measured value equation system with the sample sequences and the grid parameters for k=1, 2 to N measurement times with the sampling period T.