Current Transformer Magnetic Circuit Thermal Gap Control
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Solution Overview
Problem
Current transformers experience significant heating due to energy losses in the magnetic circuit when operating at higher frequencies or with high-frequency currents, leading to temperature increases that can damage adjacent electrical or electronic components.
Innovation Solution
Incorporating a device that varies the magnetization of the magnetic circuit in response to temperature increases, such as bi-metal strips or materials with a lower Curie temperature, to create gaps and limit magnetic flux, thereby reducing iron losses and heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the current transformer operates at higher frequencies or with high-frequency currents, then the energy transfer capability is improved, but the iron losses increase causing significant heating of the magnetic circuit
Solution Approach 1:
The magnetic circuit incorporates a movable element that can dynamically adjust the gap size in response to temperature changes. When temperature increases due to high-frequency operation, the element shifts to increase the gap, automatically reducing magnetic flux and iron losses without manual intervention or external control systems
Solution Approach 2:
The invention changes the physical parameter of the magnetic circuit by introducing a variable gap that adjusts with temperature. This parameter change modifies the magnetic reluctance, thereby controlling the magnetic flux density and reducing iron losses at elevated temperatures while maintaining efficient energy transfer at normal operating conditions
2Power
If the current transformer operates at higher frequencies, then the energy transfer capability is improved, but the temperature of the magnetic circuit increases
Solution Approach 1:
The magnetic circuit employs a self-regulating mechanism where temperature-induced thermal expansion or thermal stress automatically adjusts the gap size. The system serves itself by using the temperature change as the actuating force to reduce magnetic flux and consequently reduce further heating, creating a self-balancing thermal management system
Solution Approach 2:
The invention converts the harmful effect of temperature increase into a beneficial automatic protection mechanism. The thermal expansion or thermal stress that would normally be considered a problem is instead utilized as the driving force to open the gap and reduce magnetic flux, thereby converting the harmful temperature rise into a self-protective response that limits further heating
3Temperature
If a device for varying magnetization is added to the magnetic circuit, then the temperature control is improved, but the device complexity increases
Solution Approach 1:
The temperature control function is achieved through a self-actuating mechanism that uses thermal expansion or thermal stress of materials already present in the magnetic circuit. No external actuators, sensors, or control systems are required - the thermal effects themselves drive the gap adjustment, maintaining simplicity while achieving effective temperature control
Solution Approach 2:
The invention utilizes thermal expansion of materials within the magnetic circuit to automatically adjust the gap size. As temperature increases, the thermal expansion of specific components causes the gap to open, reducing magnetic flux and iron losses. This approach achieves temperature control through a passive physical effect rather than an active control system, minimizing added complexity
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 effectively limits magnetic flux and reduces heating by up to 50% without significantly impacting energy transfer at nominal current levels, ensuring the magnetic circuit operates safely and efficiently.
Implementation Method 1
the mechanical device comprises bi-metal strips, which are mounted head-to-tail and are housed in a recess in order to effect a separation of the magnetic circuit, generating a gap
Implementation Method 2
the static device being made up of a magnetic material having a Curie point or a Curie temperature that is lower than that of the magnetic material of the magnetic circuit
Implementation Method 3
When the fundamental frequency of the electricity grid increases and exceeds 100 Hz or when a high-frequency current or current harmonics are superposed on the load current circulating in the primary conductor 3, energy losses are generated in the iron of the magnetic circuit
Implementation Method 4
The material of the static device comprises cutouts for avoiding current losses through eddy currents
Data Source
AI summary
The current transformer includes a magnetic circuit made of magnetic material that is intended to be placed around a primary conductor, and a secondary winding that is wound onto a portion of the magnetic circuit in order to deliver a secondary current to processing circuits. In this current transformer the magnetic circuit includes at least one device for varying the magnetization of a portion of the magnetic circuit according to the temperature in order to limit or to decrease the magnetic flux in the magnetic circuit when the temperature of the magnetic circuit increases. The protection device and the electrical circuit breaker include such a transformer.