System for Measuring of Radial Clearances in Gas-Turbine Engine with Self-Compensation of Temperature Effects on the Sensor

Abstract

The paper presents the description of developed hardware, algorithms and software of the system for measuring of radial clearances between stator and blade tips in the compressor of gas-turbine engine. The measuring system implements the method with self-compensation of temperature effects on the eddy-current single-coil sensor with a sensitive element in the form of a conductor segment. Due to the self-compensation the number of used sensors and related mounting holes in the power plant stator was reduced. The core operations of the self-compensation are realized in real time on hardware-and-software level. This makes it possible to use the system for the detection of dangerous states of gas-turbine engines during power plants operation. The previously unexplored phenomenon of "not-complete compensation" of temperature effects is considered. The phenomenon is related to the special features of the conversion of the single-coil eddy-current sensor’s informative parameter in the measuring circuit. It manifests in the difference of conversion functions of the system’s measuring channels under normal and nominal temperatures. The paper provides the way of the effect elimination by means of program correction. The results of experimental researches of the working model of the measuring system are given. They characterize the metrological appropriateness and efficiency of the system. The experimentally obtained calibration characteristic approximated by polynomial function was used to determine the systematic part of the error as a difference between the given and the calculated radial clearance. The random error was evaluated by the deviation of measured codes from an average value in the sample that was obtained at the specified value of radial clearance for the fixed blade’s position relatively to the sensor’s sensitive element. The efficiency of the working model was evaluated on the laboratory equipment during the rotation of the electrically driven compressor wheel. The quantitative estimates of speed and accuracy of the working model of the measuring system were obtained during experimental researches. They confirmed the possibility of using the system for the detection of dangerous states of gas-turbine engines applied in the electrical power industry.