Rotating Electrical Machine Press Plate Slots
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Solution Overview
Problem
Laminated press plates in rotating electrical machines experience high eddy current losses and overheating due to axial magnetic flux, leading to mechanical stress and potential electrical shorts, which increase losses and risk fault currents.
Innovation Solution
The laminated pressure plate sheets are partially slotted radially to reduce eddy current losses, with slots extending from the inner edge into the press plate, allowing better axial flow equalization and relieving mechanical stress while maintaining minimal impact on magnetic flux circulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If laminated press plates are used to guide magnetic flux and provide axial pressing force, then the structural integrity and magnetic flux guidance are improved, but eddy current losses and overheating increase due to axial magnetic flux penetration
Solution Approach 1:
The press plate is divided into multiple laminations stacked together, with insulation between layers. This segmentation interrupts the eddy current paths, reducing eddy current losses while maintaining the axial pressing force and structural integrity needed for magnetic flux guidance
Solution Approach 2:
Different regions of the press plate are designed with varying properties - the laminated structure provides electrical insulation to reduce eddy currents, while the overall plate structure maintains mechanical strength for pressing and magnetic flux guidance functionality
2Shape
If the press plate is designed with conical widening to achieve a cone angle of 15-20°, then the magnetic flux guidance is improved, but the radial component of flux increases by a factor of 1/sinδ, leading to magnetic saturation
Solution Approach 1:
The conical press plate is constructed from multiple thin laminated layers stacked together. This segmentation reduces the effective cross-sectional area for radial flux components, decreasing the flux density and preventing magnetic saturation while preserving the conical shape's flux guidance benefits
Solution Approach 2:
The press plate uses composite construction with laminated layers separated by insulation. This composite structure modifies the magnetic flux distribution, reducing the radial flux component's impact and preventing saturation in the conical region
3Force
If multiple laminations are stacked and glued together to form the press plate, then the axial pressing force is improved, but the bonding between sheets creates weak points that may fail under strong compressive forces
Solution Approach 1:
The press plate is constructed from multiple thin laminations instead of a single solid piece. This segmentation distributes the compressive stress across many layers, reducing the load on any single bonding interface and preventing failure while maintaining axial pressing force
Solution Approach 2:
By changing from a solid press plate to a laminated structure, the mechanical and electrical properties are modified. The laminated construction changes the stress distribution and bonding requirements, allowing the plate to withstand compressive forces more reliably
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 eddy current losses by limiting axial flux penetration and mechanical stress, preventing overheating and electrical shorts, thereby enhancing the operational stability and efficiency of the machine.
Implementation Method 1
The magnetic stray field from the stator and rotor end windings (17 and 17a in 1) is sucked in by the magnetic press plate and enters the press plate normal to the cone (flux lines 18 in 1). Under ideal conditions, the incoming magnetic flux (xx in 1) is taken over proportionally in each sheet and deflected in the sheet in the radial direction outwards and in the circumferential direction
Implementation Method 2
All laminations of the laminated pressure plate 14, 14' have the usual laminating insulation like the laminations of the laminated stator core. The sheets can also be coated with a baking varnish (resin in the B-stage) and are glued together under pressure and heat.
Implementation Method 3
The axial flow results in high eddy current reaction in the sheet. The eddy current reaction can lead to high temperatures.
Implementation Method 4
The eddy current reaction can lead to high temperatures. The point subjected to the maximum load is in the bottom area of the groove of the yoke.
Data Source
Figure 1~2
Figure 3a~4b
Figure 5a~7
AI summary
A rotating electrical machine, in particular a turbogenerator, has a rotor and a stator concentrically surrounding the rotor, which is bounded at both axial ends by a laminated pressure plate (14) constructed from a stack of individual press-fit laminations (30). An improvement in electrical properties is achieved by providing the press-fit laminations (30) at least partially with slots (26) to reduce eddy current losses.