Permanent Magnet Rotor Air Gaps for Thermal Expansion in LNG Motors
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Solution Overview
Problem
Permanent magnet pump motors used in LNG environments face challenges with magnet and rotor deformation or damage due to temperature changes and fluid friction, as existing designs do not adequately account for linear expansion and stress caused by temperature fluctuations and fluid friction.
Innovation Solution
A permanent magnet rotating electric machine design featuring a rotor with air gaps at both ends of the magnet insertion holes and a shoulder portion to accommodate linear expansion, along with a small-diameter rotor to reduce fluid friction, and optional protective coatings or liners to prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the permanent magnet is inserted tightly into the magnet insertion hole without air gaps, then the magnetic coupling is improved, but the magnet and rotor are deformed or damaged due to thermal expansion stress at low temperatures
Solution Approach 1:
Air gaps are intentionally designed at both end portions of the permanent magnet in the magnet insertion hole to serve as cushioning spaces. These air gaps accommodate thermal expansion and contraction of the permanent magnet when temperature changes from room temperature to low temperature (−162° C. for LNG), preventing excessive stress that would deform or damage the magnet and rotor while maintaining reliable magnetic coupling through the connecting portion
2Object-affected harmful factors
If the rotor diameter is increased to reduce fluid friction, then the fluid friction is reduced, but the rotor becomes larger and more complex
Solution Approach 1:
The permanent magnet is divided into two separate magnets arranged with the magnetic pole center and magnetization direction extending in parallel. This segmentation allows for a more compact rotor design that reduces fluid friction while maintaining the necessary magnetic field strength and avoiding excessive rotor diameter
Solution Approach 2:
The magnet insertion hole is designed with non-uniform features including air gaps at end portions and a connecting portion with different dimensions. This local variation in structure allows optimized magnetic coupling in critical areas while maintaining overall rotor compactness to reduce fluid friction
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 design effectively prevents magnet and rotor deformation, reduces fluid friction, and enhances the operational efficiency of the motor under extreme low-temperature conditions by managing stress and linear expansion, while maintaining the motor's structural integrity.
Implementation Method 1
Rare-earth magnets, such as neodymium magnets and praseodymium magnets, in particular, have a property that the permanent magnet contracts in a magnetization direction and expands in a direction perpendicular to the magnetization direction at low temperatures.
Implementation Method 2
when the machine is used under an extremely low temperature condition, such as with the LNG, air bubbles present in the filling portion expand and contract as affected by a sudden change in temperature from room temperature to low temperature or vice versa.
Data Source
AI summary
A permanent magnet rotating electric machine includes a rotor and a stator. The rotor includes: a permanent magnet forming a single pole within a rotor core of the rotor, the permanent magnet being divided into two divided permanent magnets; a connecting portion assuming an electrical steel sheet disposed between the two divided permanent magnets; and magnet insertion holes in which the permanent magnets are inserted. In the rotor, the magnet insertion holes are shaped to include: air gaps at both end portions in a width direction of the permanent magnet, each air gap being formed between a surface of the permanent magnet extending perpendicularly to the magnetization direction and a surface of the electrical steel sheet facing the surface of the permanent magnet; a shoulder portion disposed on the facing surface; and another air gap extending toward a rotor outside diameter side and the magnetic pole center side.