Rogowski Coil Current Transducer Online Calibration
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Solution Overview
Problem
Rogowski coil current transducers face challenges in achieving high accuracy due to unknown sensitivity changes from environmental conditions like temperature, mechanical constraints, humidity, and aging, which current signal processing cannot account for, leading to measurement errors and requiring additional calibration efforts.
Innovation Solution
Incorporating a third conductor winding for a calibration current signal that allows for continuous online calibration of the Rogowski coil sensitivity without interrupting the rated current measurement, using a calibration current that induces a voltage signal compatible with the rated current signal, enabling direct and accurate sensitivity adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ferromagnetic core based current transducers are used, then high measurement accuracy is achieved, but the device suffers from saturation effects and limited dynamic range
Solution Approach 1:
The patent changes the core material parameter from ferromagnetic to air-core (non-magnetic), fundamentally altering the magnetic properties of the transducer. This eliminates saturation effects and extends the dynamic range while maintaining measurement accuracy through the Rogowski coil principle and electronic integration.
Solution Approach 2:
The patent employs a composite structure combining an air-core Rogowski coil with electronic integration circuitry. This hybrid approach merges the advantages of air-core coils (no saturation) with electronic signal processing capabilities to achieve both high dynamic range and measurement accuracy.
2Reliability
If Rogowski coil current transducers are used, then high dynamic range and low weight are achieved, but measurement accuracy deteriorates due to sensitivity changes from environmental conditions
Solution Approach 1:
The patent implements a feedback mechanism where the transducer electronics continuously monitor the output signal from the Rogowski coil and apply correction based on integrated processing. This feedback loop compensates for sensitivity variations caused by environmental conditions, maintaining measurement accuracy while preserving the high dynamic range characteristics.
Solution Approach 2:
The patent replaces mechanical/physical compensation methods with electronic signal processing. Instead of using mechanical adjustments or additional physical sensors to compensate for environmental effects, the solution uses electronic integration and digital signal processing to correct sensitivity variations, thereby maintaining accuracy without adding mechanical complexity.
3Measurement precision
If temperature compensation is implemented using temperature sensors and calibration, then temperature effect compensation is achieved, but additional production effort and calibration requirements increase
Solution Approach 1:
The patent makes the transducer electronics multi-functional by integrating both measurement and compensation functions within the same electronic circuit. The electronics not only process the primary measurement signal but also inherently compensate for temperature effects through the integration process, eliminating the need for separate temperature sensors and complex calibration procedures.
Solution Approach 2:
The transducer electronics performs self-compensation for environmental effects through its inherent integration function. The system automatically corrects for temperature variations and other environmental conditions without requiring external temperature sensors or manual calibration interventions, thereby reducing production effort and device complexity.
4Ease of manufacture
If Rogowski coil current transducers are used, then lower production cost is achieved, but manufacturing precision requirements increase to ensure accurate sensitivity
Solution Approach 1:
The patent changes the approach to sensitivity determination from depending on precise mechanical winding parameters to being determined by electronic calibration factors. This allows for greater tolerance in the physical winding process while maintaining overall measurement accuracy through electronic adjustment, thereby reducing manufacturing precision requirements without increasing production cost.
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 precise and continuous calibration of the Rogowski coil sensitivity, enhancing measurement accuracy beyond conventional magnetic coil transducers and achieving IEC60044-8 class 0.2 or better without the need for additional measurement techniques or maintenance interruptions.
Implementation Method 1
When placed around a primary conductor carrying an electrical current, the Rogowski coil generates a voltage proportional to the derivative of the current according to the Ampere's law
Implementation Method 2
the secondary conductor winding (16) is adapted to induce between its pair of second terminals (17,18) a voltage signal VS′, said voltage signal VS′ being a superposition of a rated current voltage signal (VS), being characteristic for the derivative of the rated current (diR(t)/dt), and an additional calibration signal (Vcal) in response to the derivative of the calibration current signal (iCal (t))
Data Source
AI summary
The invention is about a current transducer of the Rogowski type, with a primary conductor winding having a first number of loops (N1) for carrying the rated current (IR) to be measured, with a secondary conductor winding having a pair of second terminals and a helical shape and a second number of loops (N2), said secondary conductor winding encircling the primary conductor in a toroidal manner, whereby a rated current voltage signal VS is induced between the pair of second terminals of the secondary winding, said rated current voltage signal being characteristic for the derivative of the rated current (dIR/dt), with a transducer electronics (IED) configured to receive the rated current voltage signal (VS), characterized in that the current transducer comprises a third conductor winding having a pair of third terminals with a third number of loops (N3), whereby the transducer electronics (IED) is configured to feed a calibration current signal (ICal) into the third conductor winding, whereby in response to the derivative of the calibration current signal (dl-Cal/dt) an additional calibration signal (Vcal) is created between the pair of second terminals of the second winding and whereby the transducer electronics (IED) is configured to process the rated current voltage signal (VS) and the calibration signal (Vcal) to derive a corrected voltage signal (VS,corrected) with a calibrated sensitivity Scal.