Double Roebel Bar Stray Field Compensation
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Solution Overview
Problem
Existing Roebel bar designs for directly gas-cooled turbogenerators require substantial space due to the need for massive lugs and crossing lugs to compensate for stray field voltages, particularly in retrofit applications.
Innovation Solution
The design incorporates directly gas-cooled double Roebel bars with transposed individual strands separated by an intermediate cooling tube stack, featuring cross-over bars that transpose strands over the cooling tube stack to minimize space requirements, achieving a total Roebelisation angle of 540° through sequences of 180° transpositions that either parallel, cross, or alternate across the stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional massive lugs and crossing lugs are used to compensate for stray field voltages, then stray field voltage compensation is achieved, but spatial requirements increase substantially
Solution Approach 1:
The invention changes the geometric parameters of the Roebel bar by implementing a specific transposition configuration where strands cross over the cooling tube stack at defined positions. This transposition arrangement (with specific crossing points and angles) modifies the electrical path geometry to compensate for stray field voltages while maintaining a compact form factor, thereby achieving voltage compensation without increasing overall space requirements.
Solution Approach 2:
The invention utilizes the vertical dimension by having strands cross over the cooling tube stack in the vertical direction rather than requiring additional horizontal space for massive lugs. The transposition occurs in the vertical plane, allowing stray field compensation through three-dimensional strand arrangement that does not increase the horizontal footprint of the winding.
2Reliability
If strands are transposed crossing the cooling tube stack, then stray field voltage compensation is achieved, but manufacturing complexity increases
Solution Approach 1:
The Roebel bar is segmented into distinct transposition sections, with the first transposition occurring before the cooling tube stack and the second transposition occurring after the stack. This segmentation allows each transposition section to be manufactured and assembled separately, simplifying the overall manufacturing process while achieving the required stray field compensation through the combined effect of both transpositions.
Solution Approach 2:
The cooling tube stack serves as an intermediary element around which the strand transposition is organized. The transposition configuration uses the cooling tube stack as a reference structure, with strands passing over it in a defined manner. This intermediary structure simplifies the transposition geometry compared to free-space transposition, as the cooling tube stack provides a fixed reference for the crossing pattern.
Data Source
AI summary
A stator winding of a directly cooled turbogenerator comprises directly gas cooled double Roebel bars is arranged as active parts in slots of a stator body. Each double Roebel bar has two single Roebel bars, which includes each a stack of a plurality of transposed individual strands, and are separated by an intermediate stack of cooling tubes. Mounting space is saved by constructing, for the compensation of stray field voltages, at least one double Roebel bar as a cross-over bar with the strands being transposed over the stack of cooling tubes in the middle in order to change the sides of the single Roebel bars along the active part.