Induction Machine Rotor Cooling Ducts via Slot Depth
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Solution Overview
Problem
In induction machines, the heat transfer from rotor bars to the ferromagnetic core is limited due to the stack of electrically insulated ferromagnetic sheets, restricting effective cooling, and using hollow rotor bars compromises the design flexibility of the cross-sectional profiles, affecting both cooling and electrical properties.
Innovation Solution
The rotor design features slots with a greater radial height than the rotor bars, allowing the bottom portions of the slots to serve as cooling ducts for air or fluid, with the shaft and ferromagnetic core structure incorporating bores to facilitate fluid flow, eliminating the need for hollow rotor bars and enhancing cooling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If hollow rotor bars are used to increase cooling efficiency, then heat transfer is improved, but design flexibility of cross-sectional profiles is compromised
Solution Approach 1:
The invention divides the cooling function into separate components: the rotor bars remain solid for electrical functionality, while dedicated cooling ducts (formed by slot extensions) provide the fluid flow path. This segmentation allows each component to optimize its specific function without compromise.
Solution Approach 2:
The invention introduces cooling ducts as intermediary structures that mediate between the rotor bars and the cooling fluid. These ducts serve as the interface for heat transfer, eliminating the need to hollow out the rotor bars themselves while still enabling effective cooling.
2Reliability
If the ferromagnetic core structure uses electrically insulated sheets, then electrical insulation is improved, but heat transfer capability in the axial direction is limited
Solution Approach 1:
The invention segments the heat transfer path from reliance on axial conduction through insulated sheets to radial conduction through solid rotor bars and dedicated cooling ducts. This separates the electrical insulation function (handled by sheet insulation) from the heat transfer function (handled by metal bars and ducts).
Solution Approach 2:
The invention shifts the primary heat transfer direction from axial (through insulated sheets) to radial (through rotor bars and cooling ducts). By extending cooling ducts radially and positioning them to receive fluid from the air gap, heat is efficiently removed in the radial dimension rather than being constrained by axial conduction through insulated layers.
3Temperature
If cooling fluid flow path is extended through the rotor, then cooling efficiency is improved, but structural complexity increases
Solution Approach 1:
The invention makes the slot extensions serve multiple functions: they provide mechanical support for the rotor bars (structural function) and simultaneously form dedicated cooling ducts (thermal function). This multi-functionality reduces overall structural complexity compared to adding separate cooling components.
Solution Approach 2:
The rotor structure serves its own cooling needs by using its existing slot geometry extended radially to form cooling ducts. The rotor bars and slot extensions themselves become the cooling system, eliminating the need for separate hollow structures or additional cooling components.
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
This design enhances heat transfer and cooling efficiency by direct fluid contact with rotor bars without compromising the electrical properties, allowing for effective heat removal through the air-gap surface and shaft, while maintaining mechanical strength and design flexibility.
Implementation Method 1
A rotor according to the invention comprises a ferromagnetic core structure and a cage winding which comprises: rotor bars located in slots of the ferromagnetic core structure... The radial height, i.e. the depth, of the slots of the ferromagnetic core structure is greater than the radial height of the rotor bars so that the bottom portions of the slots of the ferromagnetic core structure which are closest to the geometric rotation axis of the rotor are free from the rotor bars. Therefore, the bottom portions of the slots of the ferromagnetic core structure can be used as cooling ducts for conducting air or some other cooling fluid.
Implementation Method 2
air or other cooling fluid which flows in the cooling ducts has a direct contact with the rotor bars
Data Source
AI summary
A rotor of an induction machine includes a ferromagnetic core structure and a cage winding. The cage winding includes rotor bars and end-rings. The rotor bars are located in slots of the ferromagnetic core structure. The end-rings connect the ends of the rotor bars to each other at the ends of the ferromagnetic core structure. The radial height of the slots of the ferromagnetic core structure is greater than the radial height of the rotor bars so that the bottom portions of the slots are free from the rotor bars. Therefore, the bottom portions of the slots constitute cooling ducts for conducting cooling fluid through the rotor. As the rotor bars constitute one wall of each cooling duct, the cooling fluid has a direct contact with the rotor bars.