Split-Core Current Transformer Self-Calibration via Dual Secondary Coils

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Solution Overview

Problem

Split-core current transformers (CTs) face significant measurement inaccuracies due to air-gap variations, manufacturing tolerances, and environmental factors, making them unsuitable for high-accuracy applications like revenue-grade utility metering, and existing calibration methods are complex and difficult to maintain.

Innovation Solution

A self-calibration system for CTs, comprising two secondary coils with analog-to-digital converters and processing circuitry, samples signals to determine and update calibration parameters, reducing measurement errors by accounting for air-gap variations and other environmental factors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If split-core CT is used for non-intrusive installation, then ease of installation is improved, but measurement precision deteriorates due to air-gap variations

Engineering Contradiction:

Improveease of installationVSAvoidmeasurement precision

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The system dynamically adjusts calibration parameters based on detected air-gap variations and environmental conditions. By continuously monitoring measurement signals and adjusting parameters such as coupling factor and phase shift compensation, the system maintains high measurement precision despite physical changes in the split-core assembly.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The CT system performs self-calibration by automatically detecting its own measurement errors and adjusting its internal parameters without external intervention. The processing circuitry analyzes the relationship between primary and secondary signals, identifies deviations caused by air-gap variations, and autonomously corrects these errors through parameter adjustment.

Inventive Principle:

Principle #25Self-service

2Measurement precision

If manual calibration with passive components is used, then measurement precision is improved, but device complexity and ease of maintenance worsen

Engineering Contradiction:

Improvemeasurement precisionVSAvoiddevice complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system replaces manual mechanical calibration procedures with automated electronic parameter adjustment. Instead of physically assembling matrices of passive components or adjusting mechanical variable resistors, the system uses digital processing circuitry to automatically calculate and apply calibration parameters, significantly reducing device complexity and maintenance requirements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The CT system performs self-calibration by automatically detecting its own measurement errors and adjusting its internal parameters without external intervention. This eliminates the need for manual calibration procedures and reduces device complexity while maintaining high measurement precision.

Inventive Principle:

Principle #25Self-service

3Manufacturing precision

If traditional CT calibration methods are used, then manufacturing precision is improved, but ease of operation and productivity worsen due to complex manual tuning

Engineering Contradiction:

Improvemanufacturing precisionVSAvoidproductivity

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The CT system performs self-calibration by automatically detecting its own measurement errors and adjusting its internal parameters without external intervention. This eliminates time-consuming manual calibration procedures, allowing for rapid deployment and commissioning while maintaining high manufacturing precision through automated parameter optimization.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

Inventive Principle:

Principle #35Parameter changes

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 provides improved accuracy and ease of maintenance by automatically adjusting calibration parameters, enhancing the precision of current measurements and reducing the need for manual tuning.

Implementation Method 1

a current transformer (CT) that comprises the primary winding as the power line conductor and the secondary providing an output current inversely proportionate to the number of windings

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

the cores are made of one or more ferromagnetic materials

Methodology Applied

Scientific EffectFerromagnetism: Ferromagnetism

Data Source

PatentUS11705275B2Self calibration by double signal sampling

Publication Date: 2023.07.18 PANORAMIC POWER

AI summary

A current transformer (CT) for the purpose of, for example, current measurement, that uses a power line as a first coil and a second coil for measurement purposes, is further equipped with a third coil. Circuitry connected to the third coil is adapted to measure a signal therefrom. The measured signal from the third coil is compared to a signal measured from the second coil and based on the results, internal CT parameters are determined allowing calibration of actual results to expected results thereby providing an improved accuracy. This is especially desirable when using the CT for measurement of the like of current or phase of the primary coil when measurements are adjusted using the newly determined calibration parameters.