Turbine Shaft Overspeed Protection via Weak Section Break
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Solution Overview
Problem
Current solutions for preventing overspeed in turbomachines are either inefficient or do not effectively address all scenarios of shaft breakage, particularly when the breakage occurs upstream of the thrust bearing, leading to potential turbine rotor bursting and risk of uncontained high-energy debris.
Innovation Solution
A turbine shaft design featuring a secondary tubular segment with a larger diameter than the main segment, incorporating a weak section that breaks under excessive tangential stress, ensuring the rotor moves backward and slows down through contact with cambered stator vanes, thereby addressing all cases of shaft breakage and reducing the reliance on electronic protection systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shaft breakage protection system is implemented, then the reliability of the turbine rotor is improved, but the device complexity increases due to additional sensors and electronic control systems
Solution Approach 1:
The patent extracts the protection function from complex electronic systems and implements it through a simple mechanical feature: a secondary tubular segment with a weak section that breaks at a predetermined stress threshold. This mechanical breakage mechanism independently triggers the resistive torque element without requiring sensors or electronic control, thereby improving reliability while reducing device complexity.
Solution Approach 2:
The shaft design enables self-protection through its own structural features. The weak section in the secondary tubular segment automatically breaks when tangential stress exceeds the threshold, and the broken end automatically engages the resistive torque element on the stator, creating a self-actuating protection system that serves itself without external control.
2Reliability
If the shaft is designed with a weak section to break under excessive stress, then the overspeed protection is improved, but the strength of the shaft is reduced
Solution Approach 1:
The shaft is designed with non-uniform properties: the secondary tubular segment has a weaker cross-section compared to the main shaft. This local weakness is strategically positioned to break only when excessive tangential stress occurs during overspeed conditions, while the rest of the shaft maintains full strength for normal operation. The weak section acts as a localized sacrificial element.
Solution Approach 2:
The shaft is segmented into a strong main portion and a weaker secondary tubular segment. This segmentation allows the shaft to function as a unified strong structure during normal operation, while the segmented weak section provides a controlled failure mode for protection. The segmenting creates a hierarchical structure where different portions serve different functions.
3Loss of time
If electronic protection systems are used to detect and respond to shaft breakage, then the response time is improved, but the device complexity and cost increase
Solution Approach 1:
The patent replaces electronic detection and control systems with a purely mechanical response mechanism. The broken end of the secondary tubular segment physically engages the resistive torque element through mechanical movement when the weak section fails, eliminating the need for sensors, processors, and actuators while achieving immediate response to the breakage event.
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 ensures the rotor slows down in all cases of shaft breakage, optimizing turbine dimensioning, reducing weight and size, and minimizing the risk of overspeed-related damage, while also reducing the complexity of electronic protection systems.
Implementation Method 1
a weak section configured to break the shaft into two distinct parts when the value of a tangential stress applied to the shaft exceeds a predetermined threshold value
Implementation Method 2
ensuring the rotor moves backward and slows down through contact with cambered stator vanes
Data Source
AI summary
A turbine shaft of a turbomachine extending along a longitudinal axis (A) includes a main tubular portion with a length L1 and a maximum outer main diameter. The shaft further includes a secondary tubular segment with a length L2 and a maximum outer secondary diameter greater than the maximum outer main diameter. The secondary tubular segment extends radially from the shaft such that the main tubular portion extends on either side of the secondary tubular segment along the longitudinal axis (A). The secondary tubular segment includes a weak point that is configured to break the shaft into two distinct parts when the value of a tangential stress applied to the shaft exceeds a predetermined threshold value, and thus cause retraction of the turbine.