1. Field of the Invention
The invention relates to optical camera systems for nondestructive internal inspection of online, operating power generation turbines, including gas turbine combustor and turbine sections that are at operating temperatures in the range of over 600° C. (1112° F.) and which include combustion gas contaminants.
2. Description of the Prior Art
Infrared or visible spectrum online camera systems monitor critical internal engine components of a power generation gas turbine, steam turbine, generator or their associated equipment during their operation in a power plant, by combining a high temperature optical system with high-speed camera imagery. The optical system design requires selection and combination of lenses, optical material and related lens mounting structure, in order to provide the best image quality while surviving within the harsh operating environments of the equipment. For example, gas turbine combustors and turbine sections contain high temperature combustion gasses that damage and contaminate lens surfaces.
FIGS. 1A and 1B show schematically a known gas turbine 30 having a compressor section 32, a plurality of circumferential combustors 34 and a turbine section 38 through which passes rotating shaft 40. The turbine section 38 includes stationary row 1 vanes 42, as well as row 1 blades 44 that are rotatively coupled to the shaft 40. The turbine section 38 includes successive alternating rows of stationary vanes and rotating blades, such as row 2 vanes 46 and row 2 blades 48. The turbine 30 incorporates a plurality of inspection ports, 36, 50, and 52 to facilitate inspection access to internal components.
As shown in FIG. 1A, camera inspection system 55 is coupled to inspection port 36, and includes an optical tube housing 56 with a viewing port 57 that establishes a field of view of approximately 30 degrees aligned with the housing central axis. Camera 58 captures images transmitted by lenses in the optical tube housing 56. The camera inspection system 55 is useful for inspecting areas of interest within the turbine 30 visible in the field of view, such as for example the leading edges of row 1 vanes 42. Similarly, camera inspection system 55′ is coupled to inspection port 50, and includes an optical tube housing 56′ with a viewing port 57′ that establishes a field of view of approximately 30 degrees aligned normal to the housing central axis (i.e., a lateral or side view). Camera 58 captures images transmitted by lenses in the optical tube housing 56′. The camera inspection systems 55, 55′ are useful for inspecting areas of interest within the turbine 30 visible in the field of view. However, as shown in FIG. 1B, the known camera field of view through viewing port 57′ is only 30-34 degrees and therefore cannot capture the full width of the leading edge of turbine blade 44.
Current optical designs for real time infrared or visual light spectrum imaging of internal turbine components during online turbine operation suffer from several restrictions which limit the field of view, the maximum operating temperature, the image quality and system operating lifecycle. In order to achieve desired image quality, traditional optical systems require the use of at least one optical material with a temperature limit below 550° C. (1022° F.). In addition, traditional designs use complex groups of tightly spaced spherical lenses involving two or more elements in order to correct optical aberrations.
Traditional optical tube designs for camera imaging systems suffer from design tradeoffs among the field of view, image quality and lens mount system complexity. A larger desired field of view requires greater quantities of lenses with tighter inter-lens spacing. Conversely lens transmittance decreases as the quantity of lenses increases. These design tradeoffs have significant direct negative impact on performance and life of optical systems used in high temperature inspection applications, such as in online gas turbines, as compared to the impact on camera inspection systems used in ambient room temperature inspection applications. More specifically, in order to correct the optical aberrations, traditional optical design uses spherical lenses with a combination of different glass material with convex and concave surfaces. While being able to produce excellent image quality, traditional optical designs pose several challenges when used in a harsh turbine environment. Multiple optical materials with specific but diverse optical, thermal and mechanical structural properties need to be selected: at least one closest to the hot operating environment should have a melting temperature around 600° C. (1112° F.). Few optical materials can withstand such high temperatures without significant loss of optical properties. In order to correct for the aforementioned optical aberration, multiple spherical lenses are required. Previously known high temperature inspection system optical tube designs have used up to six different lenses to produce a sufficient image quality. Increasing the desired field of view for a wider inspection area of interest within the turbine also requires additional lenses. In practice the range/field of view in known high-temperature inspection system optical tubes is 34° or less.
Lens mount mechanical design and operational constraints as well as system useful operating life become more challenging as the number of lenses within the optical tube increases. For example it is more difficult to maintain lens alignment in high temperature inspection applications as the number of lenses in the mount increase, and useful service life suffers accordingly.
Current imaging systems used for uncooled online monitoring in “hot sections” of gas turbines have an operability limited to a maximum of approximately 200-300 hours before needing service and repair. It has been observed that the failure of the imaging system is caused by the progressive wear, breakage or misalignment of the various optical elements which are subject to the heat and vibration of the gas turbine. While this few hundred hour service duration can be sufficient for short time engine performance validation, long term operation is increasingly needed in the industry for the continuous online monitoring of internal turbine parts during their entire operating lifecycle. Gas turbines are intended to be operated continuously between scheduled maintenance cycles. The opto-mechanical components of camera inspection systems cannot be removed from a monitored gas turbine during the latter's operation, until a scheduled maintenance period. Typical maintenance inspection cycles of gas turbines are scheduled every 4000 hours, with typically a major inspection every 8000 hours. It is therefore critical for a continuous online inspection monitoring system to remain operational without disassembly at least 4000 hours before it has a chance to be inspected and serviced. So far, various attempts to increase imaging system service life have lead to marginal improvements from few tens of hours to a few hundred hours.
Thus, a need exists in the art for a high temperature environment inspection system for power system turbines and the like that can withstand continuous operation in temperature environments above 600° C. (1112° F.) and desirably up to 1000° C. (1832° F.). Another need exists for such a system with an increased field of view. Yet another need exists for such a system that reduces the number of individual lenses used in the system, in order to reduce design and operational complexity. There is another existing need to increase optical transmission efficiency while maintaining and preferably increasing image quality. There is another overall need in the art to increase high temperature inspection system operational service life so that it coincides with scheduled turbine maintenance service periods: desirably for 4000 hours.