Electric Machine Solid Stranded Conductor Skin Effect
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Solution Overview
Problem
Electric machines with high winding density suffer from increased AC copper losses due to the skin effect, particularly at high speeds and frequencies, as larger conductors have more area removed from the outer surface, reducing efficiency.
Innovation Solution
The electric machine design incorporates a combination of solid and stranded wires, where the stranded wire is positioned closer to the rotor with a total cross-sectional area within 80% to 100% of the solid wire's area, optimizing the distribution of conductors to minimize AC copper losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conductors with larger cross sectional area are used to increase winding density, then slot fill factor is improved, but AC copper losses increase due to skin effect
Solution Approach 1:
The conductor is divided into multiple parallel strands instead of using a single solid conductor. This segmentation allows current to distribute across multiple smaller surfaces, reducing the skin effect impact while maintaining the same total cross-sectional area and winding density.
Solution Approach 2:
The patent employs flexible stranded conductors that can be dynamically positioned and arranged within the slot to optimize both fill factor and current distribution characteristics, rather than being constrained by rigid solid conductor geometry.
2Ease of manufacture
If solid wire is used, then manufacturing simplicity is improved, but AC copper losses increase at high frequencies
Solution Approach 1:
The solid wire is replaced with stranded wire consisting of multiple smaller conductors bundled together. This segmentation reduces AC copper losses by increasing the effective surface area for current flow while remaining manufacturable through standard wire drawing and stranding processes.
3Loss of energy
If stranded wire with smaller cross sectional area is used, then AC copper losses are reduced, but slot fill factor decreases
Solution Approach 1:
The patent optimizes the spatial arrangement of stranded conductors within the slot by utilizing multiple dimensions - arranging strands in parallel bundles and optimizing their packing density. This maintains high slot fill factor while preserving the low AC loss characteristics of stranded construction.
Solution Approach 2:
The patent uses composite conductor structures combining multiple strands of different materials or treatments within the same conductor assembly, optimizing both electrical performance and space utilization in the slot.
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 reduces AC copper losses by distributing the current more efficiently, maintaining high slot fill factor while minimizing the impact of the skin effect, thus enhancing the overall performance of the electric machine.
Implementation Method 1
when the electric machine is operating at a high speed and generating a high frequency, AC current, the conductors experience what is commonly referred to as the skin effect where only that portion of the conductor nearest the outer surface of the conductor conducts electrical current
Data Source
AI summary
An electric machine having a stator core with axially extending slots and a plurality of windings. Each stator winding defines a continuous electrical conductor having a first wire and a second wire connected in series. The first wire defines a plurality of first axially extending segments disposed in the slots and a plurality of first end turn segments. The second wire defines a plurality of second axially extending segments disposed in the slots and a plurality second end turn segments. The first wire is a solitary wire defining a first cross sectional area and the second wire comprises a plurality of individual strands wherein each strand defines a second cross sectional area less than the first cross sectional area. In slots containing both first and second axially extending segments, the second axially extending segments are disposed closer to the rotor than the first axially extending segments.