Offset Pole Shoe Rotor Lamination for Alternator Harmonic Reduction
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Solution Overview
Problem
Synchronous alternators produce harmonic voltages due to variations in magnetic permeability caused by stator slotting, which are detrimental to equipment and require mitigation techniques to reduce harmonic content in output voltage.
Innovation Solution
The design incorporates a rotor core lamination with unskewed salient poles, where each pole body has a central axis in a radial direction and a pole shoe extending radially outward with a pole shoe arc, and the central point of the pole shoe arc is offset from the central axis, reducing harmonic voltages by minimizing variations in magnetic flux patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional rotor design with centered pole shoe arc is used, then manufacturing is simpler, but harmonic voltages are increased due to variations in magnetic permeability
Solution Approach 1:
The patent applies asymmetry by intentionally offsetting the central point of the pole shoe arc from the central axis of the pole body. This asymmetric configuration creates a more uniform magnetic flux distribution across the air gap, reducing the variation in magnetic permeability that causes harmonic voltages. The offset amount is specifically designed to compensate for the slotting effects in the stator, thereby minimizing ripple voltages and improving output voltage quality.
2Object-affected harmful factors
If skewed rotor core laminations are used, then harmonic voltages are reduced, but manufacturing complexity and difficulty increase
Solution Approach 1:
Instead of skewing the entire rotor core lamination which complicates manufacturing, the patent applies a localized asymmetric feature only to the pole shoe arc. The rotor core laminations themselves remain straight and easy to manufacture, while the pole shoe arc is designed with an offset central point. This approach achieves harmonic reduction through the asymmetric magnetic flux distribution without requiring complex skewed lamination construction.
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 configuration effectively reduces harmonic voltages in the output voltage of synchronous alternators, improving the quality of the electrical waveform and meeting stringent harmonic distortion standards, while maintaining manufacturing flexibility and avoiding the need for skewed stator cores.
Implementation Method 1
Rotating magnetic fields on the spinning rotor create electric voltages in stator windings of the stationary stator. The variation in magnetic permeability between the openings of stator slots and the steel cores causes harmonic output voltages.
Data Source
AI summary
A rotor core lamination is provided. The rotor core lamination includes a plurality of salient poles. Each of the salient poles includes: a pole body having a central axis in a radial direction of the rotor core lamination; and a pole shoe extending radially outward from the pole body, wherein the pole shoe has a pole shoe arc, and a central point of the pole shoe arc is offset from the central axis.