Insulation Resistance Measurement with Changing DC Line Voltage
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Solution Overview
Problem
Existing methods for computing insulation resistance in ungrounded DC power supply systems fail to accurately account for changes in DC line voltage, leading to measurement errors and inaccuracies.
Innovation Solution
The method involves measuring total current at two settled states of different pulse amplitudes, calculating a correction factor, and using it to isolate the measuring pulse current from the line voltage current, thereby enabling precise insulation resistance computation even at changing DC line voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a periodic square measuring pulse voltage is used to counteract measuring faults caused by external DC voltages or large system leakage capacitances, then measurement reliability is improved, but measurement precision deteriorates when DC line voltage changes occur
Solution Approach 1:
The patent applies feedback by measuring the total current at two different settled states (with different pulse amplitudes), calculating a correction factor based on the ratio of current differences to voltage differences, and using this correction factor to compensate for line voltage changes in the insulation resistance computation. This feedback mechanism eliminates measurement errors caused by DC line voltage fluctuations while maintaining the benefits of periodic pulse measurement
Solution Approach 2:
The patent changes the pulse amplitude parameter between two measurements (first pulse amplitude and second pulse amplitude) while keeping other measurement conditions identical. By varying this parameter and analyzing the relationship between current changes and voltage changes, the method isolates the line voltage effect and enables accurate correction, thereby resolving the contradiction between using periodic pulses for reliability and maintaining precision under voltage changes
2Reliability
If adaptive measuring pulses with variable clock cycles are used to differentiate between system leakage current and measuring pulse current, then measurement reliability is improved, but device complexity increases
Solution Approach 1:
Instead of using complex adaptive pulses with variable clock cycles, the patent simplifies the approach by using periodic square measuring pulse voltages with two different fixed amplitudes. This parameter change approach achieves the same goal of differentiating measuring current from leakage current while significantly reducing device complexity and ease of implementation
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 allows for accurate insulation resistance measurement by correcting for line voltage changes, reducing measurement errors and ensuring reliable computation.
Implementation Method 1
When an insulation fault has arisen, the measuring circuit closes between the network and ground via the insulation fault, meaning a measuring current dependent on the insulation resistance arises. This measuring current causes a corresponding voltage drop, which is evaluated by the electronics and leads to an alarm signal when a presettable threshold is exceeded
Implementation Method 2
In order to counteract measuring faults caused by external DC voltages or large system leakage capacitances, it is known from the state of the art to connect a periodic square measuring pulse voltage as a measuring voltage instead of a direct measuring voltage
Data Source
AI summary
A method is provided for computing an insulation resistance (Rf) in an ungrounded DC power supply system (2) at a changeable DC line voltage (Un1, Un2). In two consecutive measurements at the point in time of the respective settled state of a first and second pulse amplitude (Ug1, Ug2) of a measuring voltage (Ug) superposed on the DC power supply system (2), the insulation resistance (Rf) is computed at a changed DC line voltage (Un1, Un2). In this context, a correction factor K is derived from a measured first and second total measuring current (Im1, Im2) and from the respective current first and second DC line voltage (Un1, Un2) in order to determine the measuring pulse current (Ig1, Ig2) required for computing the insulation resistance (Rf).