Research On Diagnosis Technology For Inner Leakage Faults Within Steam Drain Shut-off Valves In Power Plants

In the thermal power plant,steam drain valves are very important parts of the unit.The steam drain shut-off valve inner leakage not only reduces the power efficiency,but also becomes a big threaten for power generation equipment.At present,lots of methods are used to detecting the leakage of valves.However,the existing methods for detection and diagnosis can not be fully effective for early detection of leakage failure,due to the serious environment in thermal power plants when compared with other type of power plants.In order to understand the real-time status of the valve leakage,the characteristic parameters of steam drain pipe temperature has been extracted to develop an online diagnosis system for detecting micro-leakage of shut-off valves on the LabVIEW platform,which based on the distribution of temperature fields of drain pipes.First of all,the relative models of draining system were obtained after the researches on the steam drain pipes.Based on the existed models,the heat transfer model with multi-layered cylindrical walls were obtained using the methods of infinitesimal sections.Meanwhile,mathematics models of steam drain shut-off valves in two different time concerning with no leakage and tiny leakage were established.After this,the characteristic temperature were extracted using "two-point temperature methods" to online diagnose the tiny failure on leaking valve.Then,factors which affected the methods of diagnose were analyzed using the single variable methods to analyze the influence of the amount of leakage and steam parameters.In order to verify the reliability of methods,an experimental platform were built,which could verify the accuracy of the proposed methods.Then,the MATLAB program of the valve temperature was embedded in LabVIEW using mathematical script node and a system of diagnosis technology for inner leakage faults within steam drain shut-off valves was developed using G programming language,which based on the relative models of draining system,the heat transfer model with multi-layered cylindrical walls and multilayered cylindrical wall under infinitesimal sections and "two-point temperature methods".Finally,the leakage data of the valve of main steam drain system in Henan DatangLinzhou power plant unit #2 was written into the system of diagnosis and temperature of four states of steam drain valves including no leakage,micro-drip,trap general leakage and severe leakage were calculated by the system of the valve temperature.Meanwhile,the graphs of functional relationships between valve temperature and the distance of main steam drain were shown on the interface of the system.After that,the levels of leakage were decided when compared with the characteristic temperature and the above four states of temperature,which prove that the system is available in the engineering application.