Hunan Fengtan Hydropower Plant is located in Mingxikou Town, Yuanling County, Huaihua City, western Hunan Province, downstream of Youshui, a tributary of Yuanshui River. The original power plant was designed with an installed capacity of 411MW, and four single-machine hydrogenerators with a capacity of 111MW were installed. The main functions of the power plant in the system are peak regulation and frequency modulation, and it is responsible for system accident standby. In the expansion project, the reservoir barrage of the former Fengtan Power Plant was used, and two diversion tunnels were set in the mountain body on the right bank of the barrage to divert water to the underground power plant, and two single-machine 211MW hydro-generator sets were installed. The water head of the power station is 61.64 m～85.72 m, and the installed capacity is 411MW. The power station is designed unattended (few people are on duty). On the premise of satisfying the overall design idea of the power station, the condition monitoring system of the expander fully considers the practicality of the site, designs from the perspective of finding and solving problems, and carries out the selection of measuring points, data measurement, result analysis and fault diagnosis according to the characteristics of the hydropower unit.

I. design ideas

with the unattended operation of hydropower stations, the idea of real-time on-line monitoring of hydropower units and then condition-based maintenance of the units has been recognized by more and more people. But in what way the state characteristics are obtained or applied; How to understand and grasp the relationship between state characteristics and mechanical failure; And how to make good use of the condition monitoring system and correctly derive the maintenance conclusion before fully understanding the characteristics of the unit. There are great differences in these three aspects.

The design process of condition monitoring system for Fengtan expander unit has made concrete efforts on these three levels, and combined with some practical experience in other hydropower plants, thus making the system more practical in the requirement of condition-based maintenance of the unit.

First of all, Fengtai Power Plant has established a fully automatic state measurement and analysis system, which can continuously and automatically record state information, automatically classify state information, and automatically perform real-time signal analysis (including time domain analysis, frequency spectrum analysis, axis trajectory analysis, axis attitude analysis, statistical analysis, etc.), thus ensuring that the obtained first-hand state information is completely real-time, laying a foundation for timely capturing state changes and correctly analyzing the trend changes of unit state.

Then, the state data is managed systematically and automatically by real-time analysis and processing software. Because there are a lot of measurement and analysis quantities that comprehensively describe the characteristics of the unit, it is actually impossible to select and analyze the state data without using automatic data management technology. For example, the reference background is introduced to make the data comparable in practical sense, otherwise the vibration region of the hydraulic turbine will be confused with the vibration caused by the deterioration of the state. In addition, data comparison and sample replacement are automatic.

in guiding the operation and maintenance of the unit, the system pays attention to the combination of fault identification theory and practice, and pays full attention to the temporal change of state characteristic data. In view of the complexity of actually identifying the fault mechanism, the system will mainly rely on the change of state characteristics and human experience judgment in the initial stage. However, due to the position characteristics and mechanism characteristics of state characteristics, the fault judgment is quite accurate, that is, the system can find the unit fault just after it is put into operation. After the unit operation data has accumulated to a certain extent, the system will automatically judge the state of the unit under the same working conditions and make corresponding reports, so as to guide the operation and maintenance of the unit.

II. Targeted design and system functions

Strictly speaking, the condition monitoring of the unit should include the monitoring of the operation status of the main engine and various electrical and auxiliary equipment. However, at this time, the system involved is too wide, and some technologies are not very mature, which makes some systems designed in recent years have some defects, such as too long debugging period, poor practicability of some technologies, and the whole system has not had a clear application effect after running for one to two years. This system fully considers this actual situation, and the defined unit state monitoring is firstly aimed at the monitoring of the operation state of mature main engines (including generators and turbines), and secondly, the ability to improve and upgrade the system is ensured through the modular and open design of the system. According to this design idea, the open unit condition monitoring system YSZJ of Shenzhen Zhoulida Electronic Technology Co., Ltd. was selected, and the system was put into operation around January of the project construction, and the startup test and defect treatment of # 6 unit were successfully carried out, which completely accumulated all the conditions of the main engine from power generation. It proves the practicability of this design idea under the current technical conditions.

the running state of the host includes two aspects: stability and economy. Steady-state monitoring is related to the safety and economic performance of the unit, and is the main aspect of unit condition monitoring. There are many factors that affect the stability of the unit, and the main factors are shown in the following table:

In addition, the operating parameters such as load, power factor and water head when the generator is running have an impact on the stability and economy of the unit, and the cavitation of the turbine and the efficiency of the unit also affect the stability and economy of the unit. Based on the above analysis, the following targeted functions are emphasized in the system implementation:

First of all, in order to have a clear understanding of the state of the unit, the measuring points that need to be monitored can comprehensively reflect the information of the unit. In this system design, the stability and economy of the unit are comprehensively considered in the selection of measuring points: large shaft swing, frame vibration, stator vibration, over-current component vibration, water pressure pulsation, speed, water pressure, efficiency and unit transient are set. From the effect of start-up test, the measuring points fully describe the mechanical state of the main engine and the layout is reasonable.

Secondly, in the process of project implementation, the accuracy, reliability, stability, anti-interference and reliability of the instrument are considered as a whole, which eliminates the unstable factors caused by installation conditions and makes the instrument run reliably. According to the low speed, low frequency component and the complexity of unit vibration changing with working conditions, the system has been designed, and reliable analysis results have been obtained.

thirdly, the degree of automation is high, and there is no need for personnel on duty. All typical data (fault state, transient state and normal steady state) are automatically captured, stored, analyzed, classified and managed, forming a mechanical condition maintenance sample database. In view of the special situation of complex working conditions and wide variation of vibration intensity of hydropower units, the influence of different working conditions on alarm and statistical analysis results is removed, and important information such as vibration zone distribution and vibration development trend of the units is extracted. The whole system is easy to operate, and the common analysis function realizes "one-key" operation, avoiding complicated operation process. For daily vibration monitoring and analysis, the records of start-up, shutdown, accident and load rejection can be completed automatically without manual intervention. More than 91% of the functions of the system have realized "manual-free" operation, the output interface is practical and easy to understand, and complex problems are automatically handled in the background of the system, which makes the operators get rid of the difficulty of understanding difficult professional knowledge and ensures the full use of the system.

fourthly, the system has the function of fault diagnosis based on fault location, providing detailed data of abnormal parts and deterioration level of mechanical equipment, and providing basis or parameters for unit maintenance, thus gradually forming a practical auxiliary system for condition maintenance of power plant units. The interconnection between the internal modules of the system adopts standard network software and hardware interfaces, which is convenient for expansion and practical in the field.

fifthly, in the design of the system, the problem of efficiency measurement is integrated. For the 211MW unit, monitoring efficiency has obvious economic significance, and at the same time, it also has more comprehensive reference information for maintenance evaluation and operation mode arrangement.

Sixthly, the system integrates the cavitation monitoring and analysis module, and evaluates the severity of cavitation through some phenomena characterized when cavitation occurs, and makes comprehensive observation by combining efficiency, stability, vibration, pressure and pulsation of overflow parts.

III. Conclusion

The on-line monitoring system for the unit status of the expansion project of Fengtan Power Plant is a joint research achievement of Fengtan Power Plant, Hunan Electric Power Experimental Research Institute and Shenzhen Zhoulida Electronic Technology Co., Ltd., which was installed on site in early April 2114. With the concerted efforts of all participating units, the # 6 unit status monitoring system was successfully put into operation in early May, and the startup test, counterweight test and counterweight test of # 6 unit were successfully completed.

the system design fully considers the needs of the power plant and the actual situation on site from the perspective of finding and solving problems, and draws lessons from the application experience of other power plants to improve it. It is practical and I believe it will play a good guiding role in the maintenance and operation of the unit during use. Of course, there are still some shortcomings in this design, and I hope all experts can give you guidance.