DESIGN, FABRICATION AND INSTALLATION TECHNIQUES FOR TRASH RACKS

Abstract

Trash rack for the intake of a hydroelectric development is an important item. The function of the trash rack is to keep out debris and other materials including fish carried by water which are likely to damage or otherwise render inoperative the control equipment's or the turbines. Design criteria for trash rack structure, fabrication and installation has been discussed in this dissertation. For overall economy of the design, various aspects like velocity of water, spacing and shape of bars, their vibration, head losses, cleaning arrangement have been considered. Determination of clear spacing between rack bars is important. This depends on the characteristics of the turbine to be protected and the nature of trash. As the spacing becomes closer the head loss increases. Hence the maximum allowable clear spacing should be determined. Determination of loss of head as per older formulae such as Kirschmer etc. gave lower values than the actual. Reason for this has been found to be due to not considering certain parameters which influence loss of head. An example using different formulae given by various authorities has been worked out to determine the best formula applicable. For right angle flow Berzinki's formula and for angular flow ldeltchik's formula have been found to be more accurate. Methods of minimizing loss of head considering economy have been given in detail...