Squirrel-Cage Rotor Slots for High-Speed Thermal Expansion Relief
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Solution Overview
Problem
Rotors with squirrel cages in dynamoelectric machines face limitations in maximum rotary speed and permissible temperature due to shear stresses at the connection between conductor bars and short-circuit rings, which are exacerbated by thermal expansion and centrifugal forces.
Innovation Solution
Designing the slots at the ends of the rotor's laminated core with a specific geometry that allows the conductors to move radially outward, using additional bodies connected to the base body to accommodate thermal and centrifugal forces, and optionally using cap rings for further speed enhancement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the rotor uses a cast squirrel cage with fixed conductor bars, then the manufacturing cost is reduced and production is simplified, but the maximum rotary speed and permissible temperature are limited due to shear stresses at the connection between conductor bars and short-circuit rings
Solution Approach 1:
The patent applies the dynamics principle by designing the slot geometry to allow the conductor bars to move dynamically within the slots during operation. The slots are designed with specific geometric features (such as enlarged openings or gaps in the slot walls) that enable the conductor bars to shift position radially outward when subjected to centrifugal forces at high speeds, thereby accommodating the dynamic requirements of high-speed operation while maintaining the simplicity of cast manufacturing
Solution Approach 2:
The patent applies parameter changes by modifying the slot geometry parameters (such as slot width, slot wall thickness, or introducing gaps) to create space for conductor bar movement. This geometric parameter modification allows the cast squirrel cage to accommodate thermal expansion and centrifugal displacement of conductor bars, enabling higher operating speeds and temperatures without increasing manufacturing complexity
2Ease of manufacture
If the rotor uses a cast squirrel cage with fixed conductor bars, then the manufacturing process is simplified, but the permissible temperature is limited due to thermal expansion constraints
Solution Approach 1:
The slot geometry is designed to allow conductor bars to move dynamically in response to thermal expansion. The geometric features (enlarged openings, gaps, or non-rigid slot walls) enable the conductor bars to shift position when heated, accommodating thermal expansion without generating excessive shear stresses, thus allowing higher permissible temperatures while maintaining simple cast manufacturing
Solution Approach 2:
The patent modifies slot geometric parameters (width, wall thickness, or introducing gaps) to create expansion space for the conductor bars. This parameter change allows the cast structure to accommodate thermal effects, increasing the permissible operating temperature without complicating the manufacturing process
3Speed
If cap rings are added to the short-circuit rings to achieve higher rotary speeds, then the maximum speed increases, but shear stresses caused by heat cannot be avoided and the structure becomes more complex
Solution Approach 1:
The patent extracts or removes the harmful constraint by designing the slot geometry to eliminate the fixed constraint on conductor bars. Instead of adding cap rings to constrain the short-circuit rings, the invention allows the conductor bars to move freely within the modified slots, thereby eliminating the source of shear stress without adding structural 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
Enables higher rotary speeds and temperatures while maintaining a cost-effective production method, reducing shear stresses, and allowing for a compact dynamoelectric machine design.
Implementation Method 1
Due to thermal expansion and/or centrifugal force loads during operation of the dynamoelectric machine, the short-circuit rings extend radially more than the laminated core of the rotor with the bars cast in
Implementation Method 2
Due to thermal expansion and/or centrifugal force loads during operation of the dynamoelectric machine, the short-circuit rings extend radially more than the laminated core of the rotor with the bars cast in
Data Source
AI summary
A rotor of a rotary dynamoelectric machine incudes a magnetically conductive body, having substantially axially running slots distributed around the circumference. A squirrel cage includes electrical conductors which are arranged in the slots. The electrical conductors are electrically contacted at the two end faces of the rotor by short-circuit rings. The magnetically conductive body includes a base body and at least two further additional bodies, which axially adjoin the base body. A first one of the at least two additional bodies directly axially adjoins the end face of the base body, and a second one of the at least two additional bodies and optionally any further additional body axially adjoin the first additional body. The slots have radially exposed slot portions in the axial end regions of the rotor such that the conductors can be moved radially outward.