[雙語翻譯]水利發(fā)電外文翻譯--水力發(fā)電站空化最佳工作條件的確定

1、2000 英文單詞， 英文單詞，1 萬英文字符，中文 萬英文字符，中文 3000 字文獻(xiàn)出處 文獻(xiàn)出處; Kahraman G, Yücel H L, Ta?gin Y. Identification of optimum working conditions in hydroelectric power plants for cavitation[J]. Engineering Failure Analysis, 2019,

2、 96: 168-174.Identification of optimum working conditions in hydroelectric power plants for cavitationGökhan Kahraman, Halit Lütfi Yücel, Yahya Ta?ginAbstract Turbine faults in hydroelectric power plants

3、 not only reduce the operation time of the plant, but also cause a serious loss of income. One of the most important turbine faults is the turbine wheel wear caused by the cavitation and accordingly the other machine equ

4、ipment faults which cause excessive vibration. In this study, cavitation intensity that the turbines have been exposed in operating conditions has been investigated. As a result of the calculations, optimum working condi

5、tions of the units have been determined with graphs obtained in various operating condi- tions. The obtained data can be easily applied to all hydroelectric power plants exposed to ca- vitation, and safe operating condit

6、ions can be determined.Keywords: Cavitation; Hydroelectric power plant ;Turbine wheel1. IntroductionHydroelectric power plants are the most important renewable energy source of the world's electricity supply, due to

7、low environmental impacts and low operating and maintenance costs. Hydraulic power has many potentials that have not been used yet. Hydroelectricity is one of the most sustainable sources of clean energy that is best sui

8、ted to environmental legislation such as Kyoto Protocol. Hydroelectric power plants do not produce greenhouse gas emissions because they do not use fuel and pollute the air. They contribute prevention actions against glo

9、bal warming About 16% of the world's electricity production is provided by hydroelectric power [1]. Hydroelectric power plants do not pollute the environment as much as thermal power plants. But as the dam site is fl

10、ooded, changes in the surrounding area can take place.In hydropower plants, the amount of energy to be generated from the water source depends on the amount of the water and the water flow. According to these two main pa

11、rameters, the turbine type to be used is determined. The turbine varieties are grouped into two main categories as impulse turbines and reaction turbines [2]. For example, pelton is an impulse turbine, Francis and Kaplan

12、 are reaction turbines. The classification of the turbines is necessary to distinguish the failure mechanism that can occur in the turbine. There are generally four reasons for failure in turbine types which are used to

13、convert mechanical energy to electrical energy. These reasons are cavitation, erosion, fatigue and material errors. These failures can affect impulse and reaction turbines differently [3]. For example, while a reaction t

14、urbine is often damaged due to cavitation, an impulse turbine is likely to be damaged due to erosion [4]. Cavitation in hydraulic machinery presents unwanted consequences such as flow instabilities, excessive vibrations,

15、 damage to ma- terial surfaces and degradation of machine performance [5,6]. If the pressure in any region of hydraulic flow of a hydraulic turbine, which is in motion between the regulating blades or the impeller blades

16、 drops to the value of the evaporation pressure of the water, this will cause the evaporation of the water in this region and the formation of vacuum volumes filled with the saturated water vapor inside. When these volum

17、es expand and grow in accordance with the general fluid motion, and suddenly disappear, high volume strikes caused by the collision of the and then many holes appear on the surface of the material. These small holes are

18、getting bigger and deeper in time due to cavitation at the end of a certain operation period material surface turns into a kind of sponge. As a result of this transformation on the turbine wheel surface material loss has

19、 been observed and vibrations in rotating mass cause major economic damage. Fig. 2. shows a turbine wheel wing exposed to cavitation.2. Material and methodThe pressure fluctuations created by the cavitation intensity can

20、 match the frequencies of the mechanical parts of the turbine and cause strong damage [13]. Better knowledge of cavitation is needed to increase the working range of the Francis turbine [14]. A lot of research has been r

21、ealized so far to determine the cavitation that the reaction turbines are exposed to. The pioneer of these in- vestigations is Prof. Thoma and the obtained results are called as theThoma cavitation factor “σ” [15,16].Acc

22、ording to Professor Thoma, the boundary value of the cavitation phenomenon that can occur in a Francis or Kaplan-type hydraulic turbine is given in eq. 1 [15,16].Ót= ≥Ócritical

23、 （1）𝐻𝑎 ? 𝐻𝑣 ? 𝐻𝑠𝐻𝑛In the equation, σt denotes the number of dimensionless thomas, and σ_ denotes the critical number of thomas

24、, which is the upper limit value of the critical cavitation. Ha shows the atmospheric pressure (mss) at the site where the plant is located, Hv shows the evaporation pressure (mss) of the water used fin the plant, Hs sho

25、ws turbine suction height (m) and the Hn shows hydraulic dip (m) value [17].As the altitude of the place where a hydraulic power plant is located increases, the atmospheric pressure drops. The atmospheric pressure drops

26、and the evaporation of the water becomes easier. It is therefore necessary to consider the value of the atmospheric pressure, that is, the altitude of the place where the plant is located, as a factor affecting the cavit

27、ation phenomenon. The atmospheric pressure at the location of a hydraulic plant is given in Eq. 2.Ha=10.33- （mss） （2）𝑍900The higher the temperature of the supply water that cons

28、titutes the hydraulic current environment of a hydraulic turbine, the easier it starts cavitation. This is because the higher the supply water temperature, which constitutes the hydraulic current environment, affects the

29、 evaporation pressure (Hv) and evaporation becomes easier as the water temperature increases. Table 1 shows the evaporation pressure of water depending on the supply water temperature.Suction height is an important param

30、eter for cavitation in Francis and Kaplan type turbines. As it can be understood from Eq. 1, since the value of Hs is positive, i.e. the downstream level is below the turbine wheel level, σt will reduce the value of the

31、dimensionless number, thus increasing the possibility of operating the turbine in the cavitation zone. For this reason, in the Francis and Kaplan turbines, the central downstream level is established above the turbine tr

32、ack level. Turbine suction height is shown in Fig. 3. σcritical is an important dimensionless number in terms of determining whether the turbine is operating in a cavitated region. The number of σcritical dimensionless i

33、n Francis turbines varies depending on the number of specific cycles (ns) and is given in Table 2 [15].The specific number of rotations is calculated according to the formula given in Eq. 3 [18].ns=(3)𝑛 ? ⻓