Study On The Working Of Penstock And Spiral Case With Elastic Layer

The penstock and spiral case with elastic layer are defined as a engineering measure of having flexible layer material surrounding it to meet the needs of bearing loads in structure. In early stage, people think that penstock itself can sustain full inner water pressure after having elastic layer surrounding it, while the concrete structure arounding it will not share the internal water pressure any more, and that embedded penstock without elastic layer sustains few pressure and pass major part of pressure on to the outside concrete structure. On the basis of observing prototype of penstock and spiral case with elastic layer, the measure of having elastic layer outside metal pipe can be taken to adjust the proportion of pressure among pipe and outside concrete structure. In the previous research and engineering practice, the study about both penstock and spiral case with spiral layer were conducted firstly with parameters of elastic layer and related structure, and then followed by finite element analysis, with no fully recognition of elastic layer parameters concerning the stress status of structure and the internal water pressure. No simple and effective analytical calculation methods about the penstock or spiral case with elastic layer have been brought forward to meet the needs of engineering practice, and also no systemic research about the layer material have been made. Since 1990s, turbine unit with 700MW capacity of single set has been adopted in large scale hydropower station. Embedment without elastic layer, both concreting with low internal pressure in the spiral case and integrating spiral case with outside concrete structure tofully bend the load has been successfully adopted. But among the above two forms, the former has the drawback of high costs and long construction period, the later the shortcoming of more consumption of reinforcement, bad quality controlling and much wider crack in concrete. Spiral case with elastic layer has basically overcome these defaults. However, its effect on running stability of the turbine unit is the most concerns remained in the engineering circles, and with no solution in previous study .On the basis of explication of practice of penstock (spiral case) with elastic layer, the stress status of structure and how the elastic layer and related structure parameter to adjust the portion of water pressure among metal-plate and outside concrete structure is systematically analyzed with finite element method and analytical method in the paper. The analysis has also been made on about the effect on running of the turbine unit under its different embedment. The achievements of the study are as follows: carrying out a series of analytical formula about penstock ( spiral case ) with elastic layer, testifying when feasible in technique and reasonable in economy, the running stability of the turbine unit can also be guaranteed. The above achievement has raised the level of application of penstock ( spiral case ) with elastic layer from engineering experience to a theory with a uniform analytical calculation. The results of its dynamic analysis has gained the acceptance of manufacturer of turbine units and related employer, and the way of embedment with elastic layer around the spiral case will be put into use in LAXIWA hydropower station with the highest head and the largest capacity of single unit.