0 Introduction To smoothly carry out condition-based maintenance work in hydropower plants, an accurate and comprehensive assessment of the condition of the turbine generator units and their auxiliary equipment is essential. The turbine governor is a crucial auxiliary device in the turbine generator unit; its condition directly affects the power supply quality of the generator and impacts the safe, stable, and economical operation of the turbine generator unit. An effective, comprehensive, and objective method for evaluating equipment condition is to conduct online monitoring of the equipment's condition performance parameters and compare the monitored operating parameters with relevant instruments and regulations to assess its condition performance. Since large and medium-sized turbine governors are microcomputer-based, highly intelligent regulating devices with diverse hardware structures that are trending towards integration and modularization, resulting in increasingly compact external structures, it is challenging to comprehensively assess the condition performance of the turbine governor by monitoring the performance parameters of its various components online during field operation. Meanwhile, because the turbine governor is part of a complex system involving water, machinery, and electricity, the regulated and controlled system will inevitably affect the governor's performance to varying degrees. Therefore, simply monitoring certain state parameters of the turbine governor, such as speed (frequency), guide vane opening, blade angle, and power, is insufficient for a comprehensive and objective assessment of its performance. It must be considered within the context of the entire regulated and controlled system. Thus, to verify the performance of the turbine governor during operation, a series of tests are typically conducted, including static characteristic tests and dynamic characteristic tests such as start-up and shutdown, no-load oscillation, no-load disturbance, sudden load increase/decrease, and load shedding. Actual turbine governor tests are generally divided into dry-state tests and wet-state tests. However, using simulation technology, wet-state tests can be performed in a dry state, allowing for early prediction of equipment maintenance quality and early detection of equipment defects, providing a reliable basis for hydropower plant maintenance. [b]1. Principles and Methods of Governor Simulation[/b] There are two modeling methods for governor simulation: digital simulation and experimental simulation. Digital simulation involves artificially constructing a mathematical model of the unit. The model is input into a computer, and then this computer with measurement and control functions is connected to the governor. The model in the computer replaces the real unit, and the simulation test is carried out using software. Due to technical reasons, there are certain differences between the artificially constructed model and the actual unit model. The accuracy of the simulation test is not very high, and it is difficult to use state analysis software to determine whether its regulation quality has changed. At the same time, since artificial model construction requires human intervention, it is difficult to automate the simulation test. Experimental simulation is very different from digital simulation in terms of constructing mathematical models and experimental methods. Its modeling principle is: if the unit being simulated has previously undergone a dynamic characteristic test (such as no-load disturbance, load shedding, etc.), and the test was very successful, then the data recorded during the test already implicitly contains all the characteristic parameters of the unit (including the comprehensive characteristic curve of the turbine, the Ta of the generator, and the TW of the water intake system, etc.). Under the same operating conditions, if the previous test is repeated, as long as the control characteristics of the speed governor (and related mechanisms) remain unchanged, their transient process curves should be the same. Based on this principle, the previous test file can be saved as a template file, and it can be retrieved each time a simulation is performed. A realistic model of the speed governor is constructed using certain mathematical methods, and a real-machine simulation test is conducted. The curves from this test are compared with the curves in the template file, and the state analysis software is used to analyze whether the test was successful and to determine whether the regulation characteristics of the speed governor (and related mechanisms) have changed, and by how much. The use of computer-automated model construction makes it possible to automate the simulation test. [b]2 Accuracy Analysis and Verification Methods[/b] Real-machine simulation is based on measured sampling data, and its realistic model is constructed using certain mathematical methods. Its error mainly comes from two aspects: the accuracy of the sampling signal and the calculation accuracy of the mathematical model. The accuracy of the sampling signal is generally between 0.2% and 0.1%, while the calculation accuracy of the computer can be controlled at a very high level, generally above one ten-thousandth. Therefore, the overall accuracy can be better than 0.2%. Because the accuracy of the real-machine test simulation is very high, it provides a high degree of reliability for the equipment condition analysis of the governor. The method for verifying the accuracy of the real-machine test simulation is relatively simple: perform a real dynamic characteristic test on the unit (such as a load shedding test), or consult relevant historical data; after shutdown, perform the same real-machine simulation test in a waterless state; the curves of the two tests should completely overlap. 3. Hydro-turbine Governor Condition Monitoring System Based on Real-Machine Simulation Test The governor condition monitoring system consists of two main parts: hardware and software. The hardware includes: a computer, a high-speed data acquisition system, a high-precision digital frequency converter, a high-precision digital frequency measurement device, a stator current detection module, and corresponding sensors. The software includes: all governor test software, real-machine simulation modeling software, real-machine simulation software, condition analysis software, online monitoring software, communication and plotting display software package, database, and trend analysis software. If the governor's condition monitoring is integrated into a unit's condition monitoring system or computer monitoring system, some hardware (such as computers and high-speed data acquisition systems) can be directly referenced from the monitoring system's computer without additional configuration. Only dedicated hardware such as digital frequency converters, digital frequency measurement, stator current detection, and sensors needs to be configured. For the software, the test software package, real machine simulation modeling software, real machine simulation software, condition analysis software, and online monitoring software can be placed on the lower-level computer, while the communication plotting and display software package, database, and trend analysis software can be placed on the upper-level computer. During unit operation, the online monitoring software is used to perform simple monitoring and analysis of the governor's operating status. During unit overhaul or initial commissioning, the test software package can be used to complete the governor's static and all dynamic characteristic tests, and test files with good adjustment characteristics can be selected as template files and stored in the template library. Afterwards, whenever the unit undergoes minor repairs or is shut down without water, real machine simulation tests can be performed. A scheduling program is designed to arrange the timing and sequence of simulation tests, ensuring complete automation. The simulated test files and analysis results are automatically transmitted to the upper-level computer and stored in the database, and can also be displayed and printed. The trend analysis software of the host computer retrieves simulation test files from the database over the years for trend analysis, and concludes whether the speed governor needs major overhaul, thereby realizing condition-based maintenance of the speed governor. 4. Two important significances of real machine simulation of speed governor a. Realize the condition analysis and condition monitoring of the speed governor. b. Load shedding simulation can replace real load shedding. After a major overhaul of the unit, a load shedding test is often carried out to check the regulation and control characteristics of the speed governor and related mechanisms. Load shedding test not only requires application to the dispatching department, but the load shedding of large units also has a great impact on the system and the unit, affecting the life of the unit. Load shedding simulation test can completely simulate real load shedding, thus replacing it. This ensures the quality of maintenance, improves efficiency, and extends the service life of the unit. [b]5 Application prospects[/b] At present, hydropower plants in our province use a variety of speed governors, but most of them have been upgraded to microcomputer-based speed governors, which provides a good application background for implementing real machine simulation of speed governors using simulation technology. Utilizing real-machine simulation technology allows for the assessment of governor overhaul quality and the timely detection of potential problems before water filling, providing strong technical support for the entire overhaul process. With the further development of condition-based maintenance, conducting real-machine simulation tests on governors at hydropower plants has become imperative. Comparisons between simulation tests conducted at the Zhexi Hydropower Station and actual machine measurements during the transition process demonstrate the convincing results of governor real-machine simulation tests. As our understanding of governor condition-based maintenance deepens, the application of governor real-machine simulation testing technology for condition monitoring and performance evaluation will be further enhanced.