Study On The Method For Measuring Flowing Steam Wetness With Microstrip Gap Capacitance Resonator

Turbine exhaust steam humidity brings the problems of working efficiency, safety of the steam turbine unit, development and manufacturing of low pressure steam turbine.Theoretical mechanism of wet steam is based on the research on humidity measurement technology, it helps to understand working status and operational efficiency of stages in wet steam area of steam turbine, and provides references for optimization design and structure improvement of steam turbine. Therefore, the accurate measurement of turbine steam humidity has important theoretical significance and practical value. Currently, it has developed a variety of different steam humidity measurement method by using different physical characteristics of wet steam. Microwave resonator perturbation measurements is a method using wet steam dielectric properties, by measuring the impact of microwave devices’ frequency to achieve the purpose of measuring steam humidity online. Compared with the microwave resonator, the microstrip resonator has a great advantage in the structure, size, price and production process among the microwave methods of measuring humidity, thus, it is a worthy method.This paper discussed the theoretical research and simulation modeling for measuring turbine steam humidity by microstrip gap resonator. A new method of measuring microstrip gap capacitance by the microwave parameters network is presented, and does research in how the air dielectric constant affects the equivalent capacitance of microstrip gap by HFSS which is the software of electromagnetic simulation, finally, the relationship is established between steam dielectric constant and resonant frequency to achieve the purpose of online measuring the turbine steam humidity. In the design of the model, firstly, microstrip gap resonator humidity measurement simulation model based on the microwave measurement method and perturbation theory is established to Verify the feasibility of microstrip gap resonator model in measuring humidity system. Futher more, the microstrip gap is widen and microstrip is capped for model, and the simulation model is established corresponding thereto gap resonator model in order to optimize the measurement results. Compared to the single microstrip gap resonator model, the widening microstrip gap and the capping microstrip gap model increase the gap capacitance effectively, enlarge the influence of the model resonant frequency offset, and improve the precision of humidity measured by microstrip slot resonator model. Finally,it designs the model of rectangular holes shield box and the hole shield box according to the theory of cutting off waveguide. It not only prevents electrical radiation and external interference but also ensures the microstrip gap resonator model can contact with wet steam vapor measured adequately, determines the turbine steam humidity measurement complete model of the microstrip line ultimately, achieves the function of the real-timeonline measurement for measuring the turbine steam humidity accurately, completes the design and research of the method of measuring steam turbine steam humidity by microstrip gap resonator.