Mineral Insulated Cable Speed Sensor for High Temperature Gas Turbines
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Solution Overview
Problem
Existing gas turbine shaft speed sensors face limitations in operating temperature, with enamel insulated wire coils typically only working up to 260°C, and previous attempts to increase temperature using woven fibreglass or ceramic fibres result in bulky and non-robust designs.
Innovation Solution
The use of mineral insulated cables with a central conductor, a layer of mineral insulator such as magnesium oxide, and a metallic sheath made from non-magnetic materials like stainless steel or Nickel alloys, allowing for sensing coils that can operate up to 1000°C and providing robustness without the need for additional insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If enamel insulated wire is used for sensing coils, then the coil structure is simple and easy to manufacture, but the working temperature is limited to around 260°C
Solution Approach 1:
The patent applies composite materials by combining mineral insulator material (such as magnesium oxide powder) with metallic sheath materials (stainless steel or nickel alloy) to create a mineral insulated cable. This composite structure enables the sensing coil to withstand high temperatures up to 1000°C while maintaining structural integrity and electrical insulation properties, resolving the temperature limitation of conventional enamel insulated wire.
2Temperature
If woven fibreglass or ceramic fibres are used to increase working temperature, then the temperature resistance improves, but the sensor becomes bulky and less robust
Solution Approach 1:
The patent employs a thin metallic sheath (stainless steel or nickel alloy) as a flexible protective shell that encases the central conductor and mineral insulator. This thin-film approach provides mechanical protection and structural compactness while allowing the sensor to maintain high temperature resistance, avoiding the bulky structure associated with woven fibreglass or ceramic fibres.
Solution Approach 2:
The mineral insulated cable composite structure combines the electrical insulation properties of mineral insulator material with the mechanical strength and temperature resistance of metallic sheath, creating a compact yet high-performance sensing coil that resists temperatures up to 1000°C without increasing device complexity.
3Temperature
If unsheathed ceramic coating is applied to the coil, then the temperature resistance increases, but the coating becomes delicate and difficult to work with
Solution Approach 1:
The patent creates a composite structure where the mineral insulator material (ceramic-based powder) is embedded within a metallic sheath rather than applied as an external coating. This integration makes the ceramic material more robust and easier to manufacture, as the metallic sheath provides structural support and protection during handling and installation while both materials contribute to high temperature resistance.
Solution Approach 2:
The metallic sheath acts as a flexible protective shell that encases the mineral insulator, providing mechanical strength and ease of handling. This shell structure makes the otherwise delicate ceramic coating robust and workable, allowing the sensor to be manufactured and installed without excessive difficulty while maintaining temperature resistance.
4Temperature
If anodised aluminium wire is used, then the working temperature increases to approximately 350°C, but the wire becomes not robust and difficult to join
Solution Approach 1:
The patent combines mineral insulator material with metallic sheath materials (stainless steel or nickel alloy) to create a composite cable structure. The metallic sheath provides robustness and ease of joining, while the mineral insulator enables high temperature resistance up to 1000°C, overcoming the weakness of anodised aluminium wire.
Solution Approach 2:
The metallic sheath serves as a protective shell that encases the central conductor and mineral insulator, providing mechanical strength and robustness. This shell structure makes the wire easy to handle and join while maintaining high temperature resistance, resolving the fragility issue of anodised aluminium wire.
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 solution enables gas turbine shaft speed sensors to function reliably at significantly higher temperatures, eliminating the need for additional insulation and enhancing reliability, while maintaining sensor accuracy and robustness against high voltage conditions.
Implementation Method 1
a layer of mineral insulator (MgO) to a metallic sheath (14). The MgO provides both physical support for the central conductor and electrical insulation
Implementation Method 2
a voltage induced in a coil by changes in the magnetic flux pattern experienced by the coil, caused by movement of a body of magnetic material in proximity to the coil, is detected and/or measured
Data Source
Figure 1~2
Figure 3~4
AI summary
A gas turbine shaft speed sensor including a sensing coil comprised of a central conducting wire, the sensor and conducting wire is surrounded by a layer of mineral insulator and the mineral insulator is surrounded by a metallic, non magnetic, sheath. A sensing coil formed with this construction allows the high operating temperatures and is robust.