Rogowski Current Sensor With Segmented Coils And Common-Mode Filtering
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Solution Overview
Problem
Existing current measurement technologies, such as optical fiber sensors and current transformers, are bulky, sensitive to direct currents, and struggle with high frequency and low current measurements, while Rogowski type sensors face issues with temperature accuracy and high frequency resonances.
Innovation Solution
An electrical circuit with 2xN coils, where N is greater than or equal to 2, connected in series and featuring common mode filtering elements, a weakly magnetic core, and a guard ring, which improves common mode rejection and reduces differential mode capacitance to maintain bandwidth, using capacitive filtering elements and a shielding braid for immunity to electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high load resistances are used in Rogowski sensors to reduce thermal drift impact, then temperature accuracy is improved, but high-frequency resonances are enhanced which degrades measurements
Solution Approach 1:
The single coil is segmented into multiple coils (2xN coils) connected in series. This segmentation allows the use of lower individual resistances while maintaining the required voltage output, thereby reducing high-frequency resonances without compromising temperature accuracy.
Solution Approach 2:
The invention changes the resistance parameter by using multiple coils with lower individual resistances instead of a single high-resistance coil. The total resistance is distributed across multiple elements, reducing the impact of thermal drift and high-frequency resonances while maintaining measurement precision.
2Reliability
If common mode filtering is enhanced in Rogowski sensors, then immunity to voltage drifts is improved, but bandwidth is reduced
Solution Approach 1:
The filtering is segmented across multiple coils, each with its own common mode filtering element. This distributed filtering approach provides better common mode rejection while maintaining bandwidth because the filtering action is spread across multiple stages rather than a single heavy filtering stage.
Solution Approach 2:
The invention introduces intermediary common mode filtering elements (capacitors) for each coil that act as mediators to reject common mode voltages while allowing differential mode signals to pass through with minimal attenuation, thus maintaining bandwidth.
3Measurement precision
If fiber optic sensors are used for high-frequency current measurement, then measurement capability is achieved, but device size increases and DC measurement capability is lost
Solution Approach 1:
The invention replaces the fiber optic mechanical system with an electrical coil-based system. The Rogowski coil uses electromagnetic induction principles with air-core or weakly magnetic core coils, eliminating the need for bulky fiber optic components while maintaining high-frequency measurement capability.
4Reliability
If current transformer sensors with high permeability cores are used, then galvanic isolation is achieved, but sensitivity to DC currents increases causing core saturation
Solution Approach 1:
The invention changes the core permeability parameter from high (in current transformers) to low or zero (air-core or weakly magnetic core). This parameter change eliminates DC sensitivity and core saturation issues while maintaining galvanic isolation through the electromagnetic coupling of the Rogowski coil.
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 solution provides a compact, high-frequency current measurement device that is immune to rapid voltage and temperature variations, maintaining measurement accuracy and bandwidth, and is capable of measuring currents above 10 kHz with improved common mode rejection.
Implementation Method 1
Rogowski current sensors can also measure high-frequency currents. These sensors determine the value of a current flowing in a conductor from a voltage generated by the current in air-core coils or coils with a weak magnetic or even non-magnetic core.
Implementation Method 2
at high frequencies, common-mode filter elements are capacitive. Therefore, the common-mode capacitance (equivalent capacitance of the filter elements) that attenuates the output current of the 2N coils is equivalent to the capacitance formed by all the filter elements connected in parallel.
Implementation Method 3
To measure high-frequency currents, typically above 10 kHz, fiber optic sensors based on the Faraday effect can be used.
Data Source
Figure 1
Figure 2~3
AI summary
An electrical circuit for measuring (100) a current (I) flowing through a conductor (COND) comprising: - 2xN coils (110 to 113), N being an integer greater than or equal to 2, connected in series with one another; and - an element for filtering (120 to 123) a common mode associated with each of the 2xN coils, each filtering element being placed in parallel with the associated coil and being able to perform common-mode filtering for the 2xN coils, a core (180) of the 2xN coils having a relative permeability lower than 10, and from among the 2xN coils, N coils are wound in a direction opposite the direction of winding of the N other coils.