Analytical Research On The Surge Pressure Of Pelton Turbine And Surge Wave Fluctuation In Shaft Gate

Some of the super large and large hydropower stations are being into design,construction and operation period with the advancement of national energy construction.So there are more and more hydropower stations with high water head, small flow and long headrace pipe.Pelton turbines are usually used in these hydropower stations.At the same time, ecological unit are set up in a large scale of hydropower stations.The headrace and diversion system is asymmetric if the ecological unit and normal unit are arranged in the same diversion system because the ecological unit with a small discharge and capacity per unit.It is called surge wave superposition that water-level fluctuation of two or more shaft gates or surge shafts in a water diversion system are connected with each other.The maximum surge pressure and water-level fluctuation of pelton turbine are studied and discussed in this paper.They are combined with new problems met in the practical projects on the base of previous research results.The contents and research findingsare mainly about:(1)Research on flow characteristics of nozzle of pelton turbineWater hammer of pelton turbine is connected deeply with flow characteristics of the nozzle.The related formula is derived to show the law of nozzle opening degree and nozzle discharge are both changed in parabola shape with relative stroke with nozzle according to the study of characteristics of nozzle components.It is proved to be accurate by the test data.(2)Calculation of water hammer of pelton turbine based on parabolic flow characteristicsThe calculation formulas of direct water hammer, one phase water hammer and ultimate water hammer of pelton turbine hydropower station are derived based on the parabolic flow characteristics.It is proved that the derived analytical formula is more accurate than the traditional analytical formula for the calculation of pressure of one phase water hammer.And it is basically the same with numerical calculation.It is close between the derived analytical formula and the usual analytical formula in the calculation of ultimate water hammer, but there is a difference between the numerical calculation.The water head is always high and the constant p is small in the load rejection of pelton turbine and one phase water hammer most occurred.There is an important theoretical significance and a good application prospect of the formula derived in this paper in the calculation of the transient process of pelton turbine.(3)Research on the initial opening degree and maximum water hammer pressure of pelton turbineThe formula of the most dangerous initial opening degree τOr when the maximum surge pressure occurs in case of load rejection is derived.It is very close to the numerical calculation result.The most dangerous opening degree τOr is much bigger than the no-load opening degree according to the numerical simulation calculation of transition process such as Shenshu and Nanpai hydropower stations with pelton water turbine.Therefore, it is actually rational to take the case of part-load rejection of turbine (opening degree τOr) as the control case of nozzle end with maximum pressure in the calculation of transient process of pelton type hydropower stations.(4)Research on the closing law of pelton turbineOne section of linear or two sections of linear closing law of turbine needle valve is made according to the pressure controlling standard τOr of nozzle end and the conclusion that maximum surge pressure can happen when part-load rejection of small opening degree.The formula of closing time of one section type linear can be derived according to the conclusion above.As the closing law of two sections of linear, the opening degree of bench points and the closing speed rate can be calculated according to the derived analytical formula and also can be optimized. The results of the derived formula are consistent with numerical simulation calculation by the test model.There is some guiding significance for the optimization of closing law of guide vane of hydropower stations with pelton turbine.(5)Research on the surge fluctuation superposition of asymmetric headrace and diversion systemThe surge wave free fluctuation law of two surge shafts are studied in this paper through the setting up and solution of two-place two-order differential equations of the two shaft gates in the asymmetric water diversion system.The results show that surge wave fluctuation of any shaft in the asymmetric system are both the sum of two wave functions and this is the reason of fluctuation superposition. Two numbers without dimension μ and λ are named to represent the position change of bifurcated pipe and the change of area ratio of two shaft gates without changing the total area. The relationship of surge wave amplitude of two surge shafts and bifurcate position, the relationship of surge wave amplitude of two surge shafts and the area ratio are studied.It plays an important role inguiding the practical projects designing.The relation equation between the area of flow section and servomotor stroke on the base of the conversion of geometric relations is gotten according to the structure characteristics of pelton turbine nozzle. The relation equation of nozzle opening degree and servomotor stroke is obtained by some transformations. The orifice flow model is used in the calculation of pelton turbine in the preliminary design stage in the past on the base of assuming the linear relationship between servomotor stroke and opening degree. In this paper, the new flow equation is presented to show the relation of unit nozzle flow and servomotor stroke is parabola law on the base of orifice flow model. The flow changing situations and equal opening degree characteristics of the integrated test feature line can be better described. In the past researches of water hammer pressure, the impact factors of initial opening degree in condition of maximum water hammer pressure is only related to pipeline feature constants and water hammer constants,while in this paper, it is also related to the structure characteristics of water turbine nozzle. The surge wave amplitude of ecological units are higher than that of conventional units in the two type units parallel power station and also it brings difficulties in the construction of project. The surge wave amplitude of two shaft gates or surge shafts are devided and presented to be the sum of two cosine function. The relations of combination of surge wave amplitude and bifurcation place, that and shaft gates area are obtained. The best choice of combination principle of shaft area is obtained through not changing the total area of shafts.