The runaway speed of waterwheels and its effect on connected rotary machinery

In the selection of hydroelectric units, the operating speed of the turbines should be so chosen as to give the most efficient results under the varying conditions of operation. When the head of water is constant, the choice, unless modified somewhat by the necessary synchronous speed of the generator, should ordinarily be the speed at which the turbine will operate with the highest efficiency with the normal condition of load.