In this paper, we present a field test of temperature sensors, based on arrays of Fiber Bragg Gratings (FBG), on a co-generation steam turbine operating at the GE Oil&Gas Nuovo Pignone facility in Florence. This unit has been upgraded with new components and high efficiency stages designed by GE technicians over the last years, providing the opportunity to test and validate the FBGs sensors for temperature measurements.
Two different kind of FBGs, packaged in flexible and rigid loose tubes of stainless steel AISI 304, have been developed and adapted to Oil&Gas requirements from INFIBRA TECHNOLOGIES, following GE technicians' expertise; the temperature distribution in 44 different sensing points has been acquired, along the thickness and the surface of the turbine casing, with only 5 fiber optic acquisition channels for an extended temperature measurement range up to 500 °C.
Accurate static and dynamic temperature measurements are fundamental for operation and control of turbomachinery. Current technologies, based on thermocouples or thermo resistances, are characterized by bulky packaging and massive wiring requirements; in addition, a dedicated thermo element is needed for each acquisition point, limiting their use to a few discrete sensing points. Fiber Bragg Grating (FBG) sensors are extremely attractive for temperature measurements due to their compactness, light weight, immunity to electromagnetic interference and multiplexing capabilities in time and frequency domains. A single array of FBG sensors allows for multipoint static and dynamic high temperature measurements in harsh and hazardous environments like those of turbomachinery systems.
This paper describes in detail a novel temperature monitoring system, permanently tested for more than 3 months on a steam turbine in operation, fully demonstrating the advantages of fiber optic sensors, including the compliance with ATEX directive for operation in environment with an explosive atmosphere. The acquired data are used for thermal model validation and for optimizing the start-up, shut-down and load variations of the turbine during operation, pointing out the attention of GE Oil&Gas to address new market requirements.