Induction Rotor Groove Chamfer for Lower Eddy Current Loss
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Solution Overview
Problem
In induction machines, particularly those with a squirrel cage-type rotor assembly, magnetic flux harmonics induce eddy currents at the radially outer corner areas of rotor bars, leading to increased losses and reduced efficiency, which previous attempts to mitigate through corner reshaping have not optimally addressed.
Innovation Solution
The introduction of a chamfer region at the radially outer internal corner of the rotor groove with low magnetic permeability and high electrical resistivity effectively reduces eddy current induction while maintaining magnetic saliency for torque creation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If rotor bars are closely fitted within rotor grooves to maintain structural integrity and magnetic saliency, then torque creation is improved, but eddy currents are induced at radially outer corner areas leading to increased losses
Solution Approach 1:
The patent applies local quality by introducing a chamfer region specifically at the radially outer internal corner of the rotor groove, while maintaining the close fit elsewhere. This localized modification creates a region with different magnetic properties (lower permeability, higher resistivity) precisely where eddy currents are induced, without altering the overall structural integrity or magnetic saliency of the rotor bar-groove assembly
Solution Approach 2:
The patent changes the magnetic and electrical parameters at the corner region by introducing the chamfer. The chamfer region has lower magnetic permeability and higher electrical resistivity compared to the main rotor bar material, which directly addresses the eddy current issue by increasing resistance to eddy current flow while maintaining the necessary magnetic properties for torque generation in the main body
2Loss of energy
If corner reshaping is attempted to attenuate eddy currents while maintaining close fit configuration, then eddy current losses are reduced, but optimal results are not achieved
Solution Approach 1:
The chamfer region acts as an intermediary element between the rotor bar and the rotor groove at the corner area. It provides a transition zone with intermediate magnetic and electrical properties that mediate between the need for close fit (for torque) and the need to reduce eddy currents. The chamfer material or structure serves as a buffer that reduces eddy current induction without compromising the magnetic coupling
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 solution significantly reduces losses caused by eddy currents without compromising the performance of the induction machine, enhancing efficiency and maintaining starting torque performance.
Implementation Method 1
magnetic flux harmonics, which have been found to induce eddy currents not contributing towards the operation of the induction machines, but increase losses and reduce efficiency thereof
Implementation Method 2
the chamfer region has a relatively low magnetic permeability with respect to the rotor frame and a relatively high electrical resistivity with respect to the rotor bar
Implementation Method 3
The magnetic flux used to induce a current in the rotor bars and consequently magnetize the rotor
Data Source
AI summary
The disclosure relates to an electric induction machine in which a chamfer region is provided between each respective rotor groove and rotor bar at a position corresponding to a radially outer internal corner region of the rotor groove. Suitably, the chamfer region has a relative magnetic permeability less than that of the rotor frame, and an electrical resistivity higher than that of the rotor bar. Moreover, a minimum diameter of the chamfer region is suitably larger than a manufacturing-tolerances derived maximum clearance between the respective rotor groove and robot bar, if any.