Journal of Energy Engineering

Many existing dams will have to address issues of minimum dissolved oxygen concentration and minimum flow before they can be relicensed. All new hydropower applications also must address such issues. Although technology has been developed to reaerate hydropower releases, trade‐offs exist between oxygen levels in the release and the minimum flow provided in relation to downstream assimilative capacity. A case history beginning with the development of the aeration technology followed by the analysis of the impacts of increased dissolved oxygen concentration and river flow on assimilative capacity is presented. Testing of both in‐reservoir oxygen injection systems and turbine aeration systems is described. A modified Streeter‐Phelps model was used to evaluate the effectiveness of aerating the releases and increasing the minimum flows from the dam. The effects of reducing municipal and industrial waste load on dissolved oxygen concentration were also compared to the effects of aerating the releases and changing minimum river flow. For this particular case, increasing minimum flows was found to be one of the most attractive alternatives for increasing the minimum dissolved oxygen concentration predicted in the river.

This paper describes the writers' experience in using an impulse relief valve and safety membranes to replace a surge tank in a small hydropower station. When the load on the generator is rapidly reduced, (load rejection), the impulse relief valve will automatically operate due to the increase in water pressure, thus, releasing a certain quantity of water to reduce the effect of water hammer and ensure safety of the unit and the penstock; this is the main principle behind this arrangement. Although it may be satisfactory to use the safety membranes alone, their use in the present project provides an additional measure of safety. Since this device acts in response to a pressure rise in the penstock, the manufacture, operation, and maintenance are simple and convenient. Use of this device in lieu of a surge tank can be economically beneficial.

Jet pumps are used extensively in hydro‐power stations in China. In this study a large number of tests on jet pumps with operating heads between 330 and 250 M have been conducted. Some elements of the testing model were changed during the testing program in order to achieve an optimum design. Test results of the jet pump with optimum sizes are presented and discussed.

The elevation of a hydroelectric turbine above or below tailwater is based on hydraulic model studies to determine the critical sigma, defined as the ratio of barometric pressure plus submergence depth at which cavitation commences divided by the rated head. Turbine model studies are undertaken by manufacturers to determine the sigma value for each model runner. This information is properietary and is never published. Consultants and utilities need to know the value of sigma during feasibility studies to establish unit setting and power plant layout. For this information, reference is usually made to published data relating sigma to other turbine parameters such as the specific speed. However, this method can result in erroneous settings, since there is a range of sigma values for each specific speed. This paper develops an alternative approach based on an analysis of over 80 recently installed turbines, wherein the turbine submergence is shown to be a function of the turbine throat velocity, the number of runner blades or buckets, the atmospheric pressure and the water temperature. The equation is applicable to Kaplan, propellor and Francis turbines with either horizontal or vertical axes. From this equation, another is derived to determine the turbine throat diameter as a function of the desired setting above or below tailwater.