Patent Application
20140064334
The subject matter disclosed herein relates generally to instrumentation systems for gas turbines or steam turbines and more particularly relates to an instrumentation rake for measuring pressure, temperatures or both.
Stationery test instrumentation for modern turbine engines measure internal conditions such as pressure and temperature at various stages along the flow path. Air pressure and temperature measurements may be made by through the use of Pitot tubes, Kiel probes thermocouples, and other devices positioned within the flowpath and elsewhere.
Typically, sensors may be disposed at various turbine locations. The sensors may be mounted on rakes attached to a surface within the turbine. A rake is generally a stationary component consisting of multiple sensors distributed along the length of a mast, usually installed radially, to obtain pressure and temperature profile information in the flow path. The sensors will typically have tubing or wires that are coupled to transducers. The tubing and wires are inserted in the mast, and consequently, the mast must have a sufficiently large diameter to enable the insertion (threading) of the tubing and wires. Space for instrumentation in a turbine is very limited. The space limitation within the turbine imposes a number of constraints on conventional rakes. For example, it is difficult to assemble and locate conventional rakes within the turbine. In conventional rakes, pressure tubing and thermocouple wiring have to be threaded through a one piece rake mast and then the Kiel probe heads are brazed or welded to the mast. Thermocouple wiring may be 40-50 ft. long and is carefully calibrated. When the thermocouple wiring is handled there is a chance that the wire may be ‘kinked’ resulting in a change of the calibration. The sensitivity of the thermocouple wiring to kinking makes threading and brazing difficult often resulting in calibration changes. In conventional rakes the pressure tubing requires internal joints for assembly (change in tubing size—joints internal to the rake mast). These joints themselves, introduce the potential for leakage. They are also sensitive to vibration and—even if successfully installed initially—may introduce leakage. Internal leaks (inside the rake mast) are difficult if not impossible to fix. The size of conventional rakes may also affect the precise angular placement and alignment of the sensors thereby limiting the number of radial measurement locations. Additionally, any internal defects to components of conventional rakes are difficult to repair.
In accordance with one exemplary non-limiting embodiment, the invention relates to a measurement rake with a first split tubular section and at least one hollow support member disposed through the first split tubular section. The measurement rake is provided with at least one sensor probe mounted on the hollow support member and coupled to a transducer and a second split tubular section attached to the first split tubular section, and forming an interior cavity on which the at least one transducer tube is disposed.
In another embodiment, a method of assembling an instrumentation rake includes disposing a sensor subassembly having at least sensor lead on an opening on a first split tubular section. The method further includes routing the sensor lead through the opening, attaching the sensor subassembly to the first split tubular section, and attaching a second split tubular section the first split tubular section.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
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The rake subassembly 11 is used to measure total pressures to determine flow profiles. The sensor probe 21 measures the total pressure (stagnation pressure). The stagnation pressure is the value obtained when the fluid flow is decelerated to zero. While the fluid flow passes through the Kiel-style pressure and thermocouple temperature sensors an accurate measurement of the pressure or temperature is recorded at varying radial heights along the rake subassembly 11.
The (two piece) rake subassembly 11 reduces the difficulty of assembly of the sensor probe 21 on the rake subassembly 11. The two-piece construction allows for the transducer tubes 27 and/or thermocouple wires to be assembled on the ‘half’ allowing for careful placement and robust connections. The two piece construction also allows a larger number of measurement elements (sensor probe pairs 39) to be installed on the rake due to easier access and simpler routing. In some embodiments, the size of the rake subassembly 11 may be reduced to an external diameter of 0.75 inches or 0.5 inches.
In one embodiment, the rake subassembly 11 may be assembled inserting the transducer tube 27 through the instrument support 19 and attaching the sensor probe 21 to the instrument support 19 thereby creating a sensor sub assembly. The instrument support 19 of the sensor subassembly then may be attached using conventional metal to metal attachment methods such as brazing, soldering, welding, and the like, to the front support member 13. The instrument support may be permanently attached (braze welded) to the front support member 13. The rear split tubular cap 29 may be welded to the front support member 13 and the weld 37 may be dressed.
The two piece embodiment of the rake subassembly 11 allows instrumentation to be reinforced against vibration by filling the instrument support 19 and/or rake mast 19 with vibration damping material, such as for example epoxy, after assembly to prevent movement of the wires or transducer tubes 27. Additionally the two piece construction of the rake subassembly 11 eliminates joints inside the rake subassembly 11. The only joint is at the probe head, outside the mast—allowing for easy repair of leaks due to poor joint construction. Because of the ease of assembly the rake subassembly 11 makes it easier to attach new instrumentation on rake masts. This instrumentation may include, but is not limited to: Kulites, optical transducers, other electronic instrumentation. Additionally, the two piece embodiment of the rake subassembly allows for the use of anti-vibration devices such as: epoxy, vibrating beam anchored in rake mast to counteract vibration, and the like.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
