Rogowski Coil Current Measurement with Capacitive Interference Correction
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Solution Overview
Problem
Rogowski coils used for AC current measurement are susceptible to significant measurement errors due to capacitive interference from the conductor, especially in low-voltage networks, and conventional shielding methods increase space requirements or have drawbacks like higher costs and larger volume.
Innovation Solution
A measuring system using a Rogowski coil with a signal processing unit and a device for correcting current values through an approximation of capacitive interference injection, determined by calibration coefficients, which allows for efficient correction without increasing space requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If shielding surfaces are used to reduce capacitive interference, then measurement precision is improved, but device complexity and space requirements increase
Solution Approach 1:
The patent extracts the capacitive interference effect from the measurement system and addresses it through mathematical modeling and signal processing. By separating the interference component from the measurement signal and using calibration coefficients to characterize the interference, the system eliminates the need for physical shielding structures, thereby reducing device complexity while maintaining measurement precision.
Solution Approach 2:
The patent replaces physical shielding mechanisms with a computational approach. Instead of using expanded metal shields, shielding windings, or housing shields to block capacitive interference, the system uses signal processing units that mathematically model and correct the interference based on calibration data, substituting mechanical shielding with electronic/software-based interference rejection.
2Measurement precision
If larger Rogowski coils are used to measure larger currents, then measurement precision is improved, but volume and weight increase
Solution Approach 1:
The patent changes the operational parameters of the Rogowski coil system by introducing calibration coefficients that characterize capacitive interference specific to each coil. This allows the use of compact Rogowski coils with smaller diameters while maintaining measurement precision through mathematical correction of interference effects, rather than requiring larger physical coils to achieve better signal-to-noise ratios.
3Measurement precision
If coupling capacitance is reduced by increasing distance between winding and conductor, then measurement precision is improved, but installation space requirements increase
Solution Approach 1:
The patent implements a feedback mechanism through calibration measurements that characterize the capacitive interference of the specific Rogowski coil-conductor arrangement. By measuring the interference characteristics under known conditions and storing them as calibration coefficients, the system can later compensate for the interference effects, allowing the use of closer winding-conductor distances without sacrificing measurement precision.
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 improves measurement accuracy by correcting capacitive interference, enabling compact and efficient current measurement without additional hardware, suitable for power monitoring devices.
Implementation Method 1
Rogowski coils are used for measuring alternating currents (AC current measurement). That involves the voltage at the output of the measuring winding of the Rogowski coils being used as a sensory variable. The voltage at the output of the measuring winding of the Rogowski coils is influenced not only by the time-varying magnetic field of the current to be measured
Implementation Method 2
In general, the conductive winding of the Rogowski coil together with all conductive surfaces of the environment form a more or less complex capacitive structure. Due to the large distances—compared to discrete capacitors—between the winding of the Rogowski coil and the conductive surfaces (e.g. surface of the primary conductor), the corresponding coupling capacitances usually have only very low values.
Data Source
AI summary
A measuring system for measuring current values pertaining to an alternating current flowing through a conductor and for correcting the measured current values regarding capacitive interference injection, includes a Rogowski coil configured inducing a voltage by way of alternating current, a signal processing device acquiring and processing values of the voltage induced in the Rogowski coil, a device determining a current value by integrating the voltage processed by the signal processing device, and a device correcting the current value regarding capacitive interference injection. The device correcting the current value is configured to make the correction by using an approximation(UADCkap1(t))of a voltage drop caused by the capacitive interference injection. The correction improves measurement accuracy without additional hardware expenditure, permitting measuring instruments using Rogowski coils to be made smaller or more compact. A method for determining calibration coefficients is also provided.