Insulation Resistance Calculation Under Variable DC Mains Voltage
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Solution Overview
Problem
Existing methods for calculating insulation resistance in ungrounded DC power supply systems with variable DC mains voltage are prone to measurement errors due to interference from fluctuating DC grid voltages, leading to inaccurate results.
Innovation Solution
The method involves recording total measuring currents at steady and fluctuating DC mains voltage states, calculating a correction factor, and using it to determine the insulation resistance from measured pulse currents and resistances, allowing for accurate insulation resistance calculation even with changing DC mains voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DC measurement voltage is applied to measure insulation resistance in an ungrounded DC power supply system, then the measurement can be performed continuously, but measurement errors occur due to interference from fluctuating DC grid voltages
Solution Approach 1:
The patent applies periodic rectangular pulse voltage with alternating positive and negative pulse amplitudes to measure insulation resistance. By using periodic pulse measurements instead of continuous DC measurement, the system can distinguish between the measurement current and the interfering DC grid voltage current, eliminating measurement errors caused by voltage fluctuations.
Solution Approach 2:
The patent uses feedback by measuring the total current during pulse application and comparing it with the expected current based on the pulse amplitude and known circuit resistances. The difference (error signal) is then used to calculate the insulation resistance, compensating for the interference from fluctuating DC grid voltages.
2Measurement precision
If adaptive measurement pulses are used to distinguish mains leakage current from measurement pulse current, then measurement accuracy improves, but incorrect measurements occur when DC mains voltage changes between steady states
Solution Approach 1:
The patent employs periodic rectangular pulse voltage with alternating polarities applied at different steady states of the DC mains voltage. By taking measurements at multiple steady states and using the alternating pulse pattern, the system can accurately distinguish measurement current from interference current even when the DC mains voltage changes, ensuring correct insulation resistance calculation.
Solution Approach 2:
The patent changes the pulse amplitude parameter to create distinct measurement conditions at different DC mains voltage steady states. By using different pulse amplitudes (first and second pulse amplitudes) corresponding to different voltage states, the system can accurately separate the measurement current component from the interference current component, maintaining measurement correctness under varying voltage conditions.
3Measurement precision
If iterative calculation with correction values is used to compensate for operating voltage differences, then measurement accuracy improves, but calculation complexity increases
Solution Approach 1:
The patent uses periodic pulse measurements at different steady states to obtain multiple current measurements. By applying the pulse voltage and measuring current at different steady states of the DC mains voltage, the system can directly calculate the insulation resistance without complex iterative corrections, simplifying the calculation process while maintaining accuracy.
Solution Approach 2:
The patent creates a simplified calculation model by measuring the total current during pulse application and using the known relationship between pulse amplitude, circuit resistances, and current to directly compute insulation resistance. This approach replaces complex iterative correction calculations with a direct measurement-based calculation, reducing computational complexity.
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
This approach enables precise determination of insulation resistance by correcting for interference from varying DC mains voltage, ensuring reliable and accurate measurements.
Implementation Method 1
This measuring current causes a corresponding voltage drop across a measuring resistor in a measuring path within the insulation monitoring device. This voltage drop is evaluated by the electronics
Implementation Method 2
When an insulation fault occurs, the measuring circuit between the network and earth closes via the fault, resulting in a measuring current that depends on the insulation resistance
Data Source
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AI summary
The invention relates to a method for calculating the insulation resistance (Rf) in an ungrounded DC power supply system (2) with a variable DC mains voltage (Un1, Un2). In two successive measurements taken at the time of steady-state conditions of a first and second pulse amplitude (Ug1, Ug2) of a measurement pulse voltage (Ug) superimposed on the DC power supply system (2), the insulation resistance (Rf) is calculated while the DC mains voltage (Un1, Un2) is changing. A correction factor K is derived from a measured first and second total measurement current (Im1, Im2) and from the respective current first and second DC mains voltage (Un1, Un2) to determine a measurement pulse current (Ig1, Ig2) required for calculating the insulation resistance (Rf).