Non-Magnetic Inserts for Salient Rotor Windage Reduction
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Solution Overview
Problem
Salient rotors in electrical machines experience excessive windage losses due to their protruding structure, which also poses challenges in maintaining magnetic performance and mechanical robustness, especially at high speeds, and existing solutions either compromise magnetic saliency or increase mass through solid metallic inserts.
Innovation Solution
The use of electrically non-conductive and non-magnetic inserts, such as T-shaped, hollow, or dovetail-shaped inserts, are positioned between the rotor poles to smooth the rotor surface, reducing windage losses without affecting magnetic performance, and are assembled with mating features to withstand centrifugal forces, minimizing added mass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If magnetic bridges are positioned between rotor poles to smooth the rotor surface, then windage losses are reduced, but magnetic saliency is negatively affected and machine performance decreases
Solution Approach 1:
A non-magnetic material insert is introduced as an intermediary between the rotor poles to smooth the rotor surface. This insert reduces windage losses by eliminating air turbulence in the interpolar spaces while being magnetically inert, thus not interfering with the magnetic field and preserving magnetic saliency.
Solution Approach 2:
The material property parameter is changed from magnetic (magnetic bridges) to non-magnetic (non-magnetic insert). This parameter change allows the insert to fulfill the smoothing function without affecting the magnetic field distribution, thereby resolving the contradiction between reducing windage losses and maintaining magnetic performance.
2Loss of energy
If solid non-magnetic metallic inserts are used to smooth the rotor, then windage losses are reduced and magnetic saliency is maintained, but the overall mass of the electrical machine greatly increases
Solution Approach 1:
A porous non-magnetic material insert is used instead of a solid metallic insert. The porous structure significantly reduces the mass of the insert while maintaining its structural integrity and smoothing function. The porous material still effectively fills the interpolar spaces to reduce windage losses without the excessive weight penalty of solid metal.
3Reliability
If metallic inserts are welded to rotor poles or secured via notch formation, then the segments are retained between rotor poles, but the assembly may lack robustness and metallic inserts are subject to eddy current losses
Solution Approach 1:
The mechanical retention system is replaced by utilizing centrifugal force during rotor rotation. The non-magnetic porous insert is designed to be retained between the rotor poles through the action of centrifugal force, eliminating the need for welding or notch formation. This substitution eliminates eddy current losses associated with metallic inserts and their associated welds.
4Loss of energy
If a smooth rotor surface is created to reduce windage losses, then friction and windage losses are reduced, but the rotor must withstand centrifugal forces at high speeds requiring mechanical robustness
Solution Approach 1:
A composite structure is created by placing the non-magnetic porous material insert between the rotor poles. The insert material is selected to provide both the smoothing function for reducing windage losses and the mechanical strength to withstand centrifugal forces at high speeds, thus resolving the contradiction between energy loss reduction and mechanical robustness.
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 significantly reduces friction and windage losses, enhances mechanical robustness, and maintains magnetic efficiency by creating a smooth rotor surface while minimizing the added mass, thus improving the overall performance and longevity of the electrical machine.
Implementation Method 1
the salient structure of such rotors contributes to the creation of excessive windage losses due to the tendency of the protrusions to catch air as the rotor rotates
Implementation Method 2
Each of the plurality of inserts comprises a mating feature formed an axially inner edge thereof that is configured to mate with a respective opening being defined by the rotor core, so as to secure the insert to the rotor core against centrifugal force experienced during rotation of the rotor assembly
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
An electrical machine 1 exhibiting reduced friction and windage losses is disclosed. The electrical machine 1 includes a stator 2 and a rotor assembly 32 configured to rotate relative to the stator, wherein the rotor assembly comprises a rotor core including a plurality of salient rotor poles 12 that are spaced apart from one another around an inner hub such that an interpolar gap 3 is formed between each adjacent pair of salient rotor poles 12, with an opening being defined by the rotor core in each interpolar gap 90. Electrically non-conductive and non-magnetic inserts 88 are positioned in the gaps 90 formed between the salient rotor poles, with each of the inserts 88 having a shape that is configured to mate with a respective opening 86 being defined by the rotor core, so as to secure the insert 88 to the rotor core against centrifugal force experienced during rotation of the rotor assembly 32.