Bridgeless Squirrel-Cage Rotor for High Overload Capacity
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Solution Overview
Problem
The existing methods for producing squirrel-cage rotors in electric induction machines, particularly those using die-casting with a bridge to facilitate the process, reduce the overload capacity of the machines, especially at high revolutions due to increased leakage flow through the bridge.
Innovation Solution
The method involves making circumferentially separated cuts in the steel sheets forming the rotor body, allowing for die-casting of rotor conductors without a bridge, thereby reducing leakage flow and enhancing the rotor's overload capacity by creating a bridgeless design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a bridge of sheet material is used to separate the rotor conductor from the air gap during die-casting, then the die-casting process can be performed while keeping the cast material within the slots, but the overload capacity of the electric machine is reduced due to increased leakage flow through the bridge
Solution Approach 1:
The bridge of sheet material is completely removed from the rotor body after die-casting. The method involves making circumferentially separated cuts in the steel sheets before stacking, then removing the bridge material after casting, thereby eliminating the source of leakage flow that reduces overload capacity while maintaining the benefits of die-casting
Solution Approach 2:
Cuts are made in the steel sheets before stacking and die-casting to prepare for subsequent bridge removal. This preliminary action enables the bridge to be easily removed after casting without compromising the integrity of the rotor conductors or the die-casting quality
2Ease of manufacture
If the bridge is present in the rotor body, then the die-casting can be performed, but at high revolutions the leakage flow saturates the bridge and part of the leakage flow passes through the air gap, reducing machine performance
Solution Approach 1:
The bridge is extracted from the rotor body after die-casting by making circumferentially separated cuts in the steel sheets before stacking and then removing the bridge material. This eliminates the leakage path through the bridge that becomes saturated at high revolutions, allowing all leakage flow to pass through the air gap where it does not affect machine performance
Solution Approach 2:
The bridge material is discarded after serving its temporary purpose during die-casting. The method enables the bridge to be used during manufacturing to facilitate die-casting, then removed afterward since it no longer serves a functional purpose and actually harms performance at high revolutions
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 approach results in a significant reduction of total leakage flow, improving the overload capacity and pull-out torque of the electric induction machine by allowing easier passage of leakage flow through the air gap rather than the bridge, thus enhancing the rotor's performance.
Implementation Method 1
die-casting of the rotor body in the sense that a stack of said sheets aligned with openings so as to form rotor slots will have said rotor slots filled by conducting material, such as of Al, for forming said rotor conductors while die-casting said rotor body
Implementation Method 2
the efficiency of the machine is increased thanks to a considerable reduction of eddy current losses in the rotor body having such sheets mutually electrically insulated
Data Source
AI summary
A squirrel-cage rotor for an electric induction machine comprises a rotor body comprising a laminated assembly of steel sheets (30) axially stacked with respect to an intended axis of rotation of the rotor. A plurality of rotor slots extend substantially axially through the rotor body and are each filled with a casted rotor conductor (36). A further slot (37) is located radially outside each rotor conductor in the peripheral surface of the rotor body and extend in parallel with the rotor conductor while forming an air gap separating peripheral steel sheet portions (38, 39) of the rotor body. Each further slot (37) extends radially to the respective rotor conductor (36) so as to extend said air gap to that location.