Magnetic Sensor for Gas Turbine Shaft Movement Detection
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Solution Overview
Problem
Existing systems for detecting abnormal movement of a gas turbine shaft, particularly those using frangible links, face challenges such as false alarms due to temperature variations, material cold flow, and the need for precise clearance to account for tolerance variations and wear, which can lead to incomplete link breakage or preservation of electrical continuity.
Innovation Solution
A magnetic sensor system that utilizes a magnetic circuit with a plunger and detection coil, sensitive to the rate of change of axial movement rather than absolute movement, eliminating the need for frangible links and operating in high-temperature environments with materials like Cobalt and Iron, generating a voltage signal proportional to the change in magnetic flux for rapid engine shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frangible links are used to detect shaft movement, then abnormal movement can be detected, but false alarms occur due to temperature variations and material cold flow
Solution Approach 1:
The patent replaces the mechanical frangible link system with a magnetic field-based detection system. A magnetic sensor detects changes in magnetic flux caused by axial movement of the shaft, eliminating mechanical contact and the associated problems of temperature-induced false alarms and material cold flow. The magnetic field sensing provides non-contact measurement that is immune to thermal expansion and material deformation issues.
Solution Approach 2:
The patent changes the detection parameter from mechanical link integrity to magnetic flux variation. By monitoring changes in magnetic flux density as the shaft moves axially, the system detects abnormal movement without being affected by temperature variations or material properties that cause false alarms in mechanical systems.
2Reliability
If frangible links with precise clearance are used, then tolerance variations and wear can be accounted for, but the system becomes complex and requires precise manufacturing
Solution Approach 1:
The magnetic detection system eliminates the need for precisely engineered mechanical clearances. The magnetic sensor can detect axial movement regardless of wear or tolerance variations because it measures magnetic flux changes directly, not mechanical gap dimensions. This substitution removes the manufacturing precision requirement entirely.
Solution Approach 2:
By changing from mechanical clearance measurement to magnetic flux measurement, the system becomes insensitive to dimensional tolerances and wear. The magnetic field penetrates through materials and detects position changes without requiring precise mechanical clearances, thereby eliminating manufacturing precision constraints.
3Reliability
If frangible links are used, then shaft breakage can be detected, but the system cannot distinguish between normal wear movement and abnormal breakage
Solution Approach 1:
The patent detects the rate of change of magnetic flux rather than absolute position. Normal wear causes slow, gradual movement that produces minimal flux change rate, while shaft breakage causes rapid movement that produces a sharp flux change rate. This rate-based detection enables differentiation between normal and abnormal conditions without additional components.
4Object-affected harmful factors
If magnetic sensor systems are used, then false alarms are reduced, but the system requires sensitive detection of rapid flux changes
Solution Approach 1:
The patent focuses detection on the rate of change of magnetic flux (dΦ/dt) rather than absolute flux values. This parameter change transforms the detection challenge from measuring small position variations to measuring the derivative, which amplifies the signal during rapid events like shaft breakage while filtering out slow wear movements. The system uses this rate-based parameter to trigger alarms only for abnormal rapid movements.
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
The system effectively reduces false alarms and compensates for wear-related movements, ensuring timely engine shutdown by detecting rapid changes in magnetic flux, thus preventing catastrophic damage while withstanding harsh conditions.
Implementation Method 1
A magnetic sensor system that utilizes a magnetic circuit with a plunger and detection coil, sensitive to the rate of change of axial movement rather than absolute movement, eliminating the need for frangible links and operating in high-temperature environments with materials like Cobalt and Iron, generating a voltage signal proportional to the change in magnetic flux
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
The present invention relates to a system (100, 300, 400) for detecting abnormal movement of a gas turbine shaft. The system comprises: a magnetic circuit (104, 302, 402) comprising a first magnetic portion (110, 304) and a second portion (112, 404), and including at least one air gap between the first portion and the second portion; and a detection coil (106) wound around the first magnetic portion. The second portion is coupled to or moveable with the shaft to reduce the air gap, on axial movement of the shaft, to change the reluctance of the magnetic circuit and thereby induce a voltage in the coil. The system may comprise a controller (108) for shutting off power to the gas turbine when the induced voltage exceeds a threshold voltage.