Stator Core Subsections Offset Unbalanced Voltages in Armature Windings
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Solution Overview
Problem
In rotary electro-dynamic machines, uneven distribution of ventilating ducts in the stator core leads to unbalanced voltage and circulating currents among strand conductors, resulting in increased current loss and local overheating due to leakage magnetic fluxes.
Innovation Solution
The introduction of sub core sections with varying space factors and transposition pitches in the stator core, which offset unbalanced voltages caused by magnetic reluctance, thereby minimizing circulating currents and heat distribution issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If ventilating ducts are arranged in the stator core, then cooling efficiency is improved, but uneven distribution causes unbalanced voltage and circulating currents among strand conductors
Solution Approach 1:
The patent introduces sub core sections with different space factors (first sub core sections with larger space factor, second sub core sections with smaller space factor) to create local variations in magnetic reluctance. This allows different regions of the stator core to have optimized characteristics: regions with larger space factor provide better cooling and reduced magnetic reluctance, while regions with smaller space factor compensate for unbalanced voltages. This local differentiation resolves the contradiction between achieving uniform cooling and preventing circulating currents.
Solution Approach 2:
The patent deliberately creates asymmetric distribution of sub core sections with different space factors around the stator core. By positioning first and second sub core sections alternately or in specific patterns, the design introduces controlled asymmetry to counterbalance the asymmetric voltage distribution caused by ventilating ducts. This asymmetric arrangement of sub core sections offsets the unbalanced voltages and prevents circulating currents while maintaining effective cooling pathways.
2Manufacturing precision
If strand conductors are transposed by 360 degrees continuously, then voltage balance is improved in the winding slot, but unbalanced voltage occurs at the end portions
Solution Approach 1:
The patent divides the stator core into multiple core units along the axial direction, with each core unit containing alternating first and second sub core sections. This segmentation allows the transposition effect to be optimized in different segments: the 360-degree continuous transposition effectively balances voltages within the winding slot, while the sub core sections in different segments compensate for end portion unbalances. This segmented approach resolves the contradiction between slot voltage balance and end portion voltage balance.
Solution Approach 2:
The patent incorporates sub core sections with different space factors as preliminary compensatory measures before the strand conductors complete their 360-degree transposition. By pre-positioning sub core sections with larger space factors at specific locations, the design anticipates and counteracts the voltage unbalance that would otherwise occur at the end portions. This preliminary action of creating compensatory magnetic reluctance variations prevents circulating currents before they can develop.
3Loss of energy
If sub core sections with different space factors are introduced, then circulating currents are reduced, but device complexity increases
Solution Approach 1:
The patent changes the space factor parameter of the stator core by introducing sub core sections with different space factors (larger and smaller) while maintaining the same basic structural configuration. Instead of adding entirely new components, the design varies a key parameter (space factor) of existing core sections to achieve voltage balancing. This parameter-based approach reduces circulating currents without proportionally increasing device complexity, as the sub core sections are integrated into the existing stator core framework.
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 reduces circulating current losses and suppresses local overheating in the armature winding by balancing voltage distribution across the strand conductors, enhancing cooling efficiency and maintaining temperature within rated limits.
Implementation Method 1
When AC current flows through multiple strand conductors of such a configuration, a leakage magnetic flux that crosses the winding slot in the circumferential direction occurs, thereby a voltage caused by EMF is induced to between the strand conductors
Implementation Method 2
The introduction of sub core sections with varying space factors and transposition pitches in the stator core, which offset unbalanced voltages caused by magnetic reluctance
Data Source
AI summary
Sub core sections are arranged at the end portions and the center portion of a stator core, and strand conductors are twisted and transposed by 360 degrees continuously toward the extending direction of winding slot. The length corresponding to transposition pitch 180 degrees of the strand conductors of the stator core is set as one core unit area, the sub core sections including portions whose space factors are different are arranged such that the sum of voltages in the strands induced in the strand conductors in the odd-numbered core unit area from one end portion of the stator core offsets the sum of voltages in the strands induced in the strand conductors in the even-numbered core unit area from the end portion of the core.