Magnetic Keeper Element Prevents Stator Magnet Demagnetization
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Solution Overview
Problem
Stator permanent magnet machines face a risk of demagnetization during the high temperature Vacuum Pressure Impregnation (VPI) process, especially when using low cost, low thermal stability Dysprosium-free or Reduced Dysprosium permanent magnets, as the high temperature cure can expose these magnets to demagnetization if no special precautions are taken to ensure their load line remains above the demagnetization knee.
Innovation Solution
A magnetic keeper element is positioned on the stator during the VPI process, formed as a ring-shaped element or other shapes, made of soft magnetic material with high permeability, to close the magnetic flux path of the permanent magnets through a low reluctance path, setting their operating points above the demagnetization threshold, thereby preventing demagnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature VPI process is performed to improve thermal conductivity and dielectric strength, then thermal performance and reliability are improved, but permanent magnets may undergo demagnetization
Solution Approach 1:
A magnetic keeper element is introduced as an intermediary component between the permanent magnets and the environment. This keeper element provides a low reluctance path for magnetic flux, acting as a mediator that prevents demagnetization during high temperature VPI processing while allowing the thermal benefits of the process to be realized.
Solution Approach 2:
The magnetic keeper element is positioned on the stator before the VPI process begins. This preliminary placement ensures that the permanent magnets are protected from demagnetization before the harmful high temperature exposure occurs, allowing the VPI process to proceed without risk to the magnetic properties.
2Ease of manufacture
If Dysprosium-free or Reduced Dysprosium magnets are used to reduce cost, then manufacturing cost is reduced, but thermal stability and resistance to demagnetization are reduced
Solution Approach 1:
The magnetic keeper element serves as a protective intermediary that compensates for the reduced intrinsic thermal stability of Dysprosium-free or Reduced Dysprosium magnets. By providing external magnetic support during the vulnerable VPI process, the keeper enables the use of these lower cost magnets without sacrificing reliability.
Solution Approach 2:
The invention changes the magnetic circuit parameters by introducing the keeper element, which alters the operating point of the permanent magnets. This parameter change allows the use of magnets with lower inherent thermal stability by externally controlling the magnetic flux path to prevent demagnetization.
3Reliability
If magnetic keeper element is positioned on stator during VPI process to prevent demagnetization, then demagnetization is prevented, but device complexity increases
Solution Approach 1:
The magnetic keeper element is a simple intermediary component that can be easily positioned and removed. Its straightforward function of providing a low reluctance path makes the process addition minimal, despite the protective function it provides against demagnetization.
Solution Approach 2:
The magnetic keeper element is a temporary component used only during the VPI process. After the impregnation is complete and the stator is cooled, the keeper element is removed. This temporary use minimizes the impact on overall device complexity while providing necessary protection during the critical processing window.
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 magnetic keeper element effectively prevents demagnetization of permanent magnets during the VPI process by maintaining internal flux density levels above the demagnetization threshold, even at elevated temperatures, allowing for the use of low cost Dysprosium-free or Reduced Dysprosium magnets and enhancing the thermal performance and reliability of electrical machines.
Implementation Method 1
the magnetic keeper element closing the magnetic flux path of the permanent magnets by providing a low reluctance flux path to magnetic flux generated by the permanent magnets
Implementation Method 2
A magnetic keeper element is positioned on the stator during the VPI process, formed as a ring-shaped element or other shapes, made of soft magnetic material with high permeability
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A permanent magnet electrical machine includes a stator 12 having conductive windings wound thereon and one or more permanent magnets 26 embedded in the stator. A magnetic keeper element 34 is positioned on the stator so as to form a magnetic flux path with the permanent magnets, with the magnetic keeper element 34 closing the magnetic flux path of the permanent magnets 26 by providing a low reluctance flux path to magnetic flux generated by the permanent magnets. A vacuum pressure impregnation (VPI) process is performed on the stator 12 to increase a thermal conductivity of the windings, with the VPI process including a curing step that is performed at a selected temperature. The magnetic keeper element 34 sets an operating point of the permanent magnets to an internal flux density level above a demagnetization threshold associated with the selected temperature at which the curing step is performed.