Flexible-Core Current Transformer for Accurate Low-Current Sensing
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Solution Overview
Problem
Current current transformers with flexible magnetic cores lack uniform flexibility in all directions, leading to accessibility issues and low accuracy in measuring low-amplitude, low-frequency currents, while solutions with high manufacturing costs or rigid structures compromise performance.
Innovation Solution
A current transformer with a magnetic circuit composed of multiple wires twisted together to form a strand, using high-permeability materials like iron-nickel alloys, and mechanical insulation to ensure flexibility and accuracy, along with a coil wound around the magnetic circuit and protected by insulating sheaths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnetic circuit with two rigid portions is used, then measurement performance is improved, but flexibility and accessibility are worsened
Solution Approach 1:
The magnetic circuit is divided into multiple thin, flexible laminated portions stacked together to form the toroidal core. Each lamination is thin and flexible, allowing the core to be bent and wrapped around conductors of various shapes and sizes while maintaining magnetic circuit integrity and minimizing air gaps through precise stacking.
Solution Approach 2:
The magnetic circuit uses laminated composite structure with thin magnetic sheets stacked and bonded together. This composite approach combines the magnetic properties needed for accurate measurement with the flexibility of thin laminated layers, resolving the contradiction between rigid magnetic circuit requirements and flexible installation needs.
2Measurement precision
If the cross section of the magnetic circuit is increased to limit air gap effects, then measurement performance is improved, but bulk and rigidity are worsened
Solution Approach 1:
Instead of using a single thick magnetic core that would be bulky and rigid, the magnetic circuit is segmented into multiple thin laminations. These thin layers are stacked to achieve the required magnetic circuit cross-section while maintaining flexibility and minimizing air gaps between layers through precise stacking and bonding.
Solution Approach 2:
The magnetic circuit employs thin laminated sheets that can be flexed and wrapped around conductors. These thin films maintain adequate magnetic circuit cross-section through stacking while remaining flexible enough for installation in confined spaces and around various conductor configurations.
3Ease of operation
If a magnetic core made of polymer filled with super-paramagnetic particles is used, then flexibility is improved, but manufacturing cost is worsened
Solution Approach 1:
The magnetic core is constructed from thin laminated sheets that can be manufactured using conventional metalworking techniques and then stacked and bonded. This segmented lamination approach achieves flexibility through the thin-layer construction rather than requiring expensive polymer-filled super-paramagnetic particle composites.
Solution Approach 2:
The invention uses conventional, inexpensive magnetic laminations instead of expensive specialized magnetic materials. The thin laminated structure provides sufficient flexibility and magnetic performance at lower manufacturing cost compared to polymer-filled super-paramagnetic particle composites.
4Ease of operation
If magnetic strips are lightly retained and fastened at each end, then flexibility is improved, but displacement variations in cross section occur, worsening measurement accuracy
Solution Approach 1:
The magnetic laminations are pre-cut to precise dimensions and pre-stack with controlled spacing and alignment. Bonding elements are pre-positioned to maintain consistent spacing between laminations, ensuring uniform magnetic circuit cross-section before the core is wrapped around the conductor and fastened at the ends.
Solution Approach 2:
The thin laminated structure allows the magnetic core to flex and conform to the conductor shape while maintaining consistent lamination spacing through bonding elements. This prevents cross-sectional area variations that would occur with loosely retained strips, ensuring measurement accuracy while preserving flexibility.
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 uniform flexibility, high sensitivity, and accurate measurement of low-amplitude currents with reduced manufacturing costs, enabling easy installation and precise measurements in confined spaces.
Implementation Method 1
The voltage induced in the winding it proportional to the rate of change (derivative) of the current in the conductor
Implementation Method 2
Devices are known with ferromagnetic cores, rather than air cores, allowing this disadvantage to be mitigated
Data Source
AI summary
An openable toroidal current transformer is intended to close over at least one electrical conductor in which an electrical current to be measured circulates. The current transformer includes a magnetic circuit, and an electrically conducting coil wound around the magnetic circuit and electrically insulated from the magnetic circuit. The coil comprises a single winding or several distinct windings coupled in series. The magnetic circuit comprises a set of wires of magnetic material assembled in the form of a strand, allowing having uniform flexibility in all directions for the magnetic circuit.