STABILIZING THE CHARACTERISTICS OF A PUMP-TURBINE IN THE RANGE BETWEEN TURBINE PART-LOAD AND REVERSE PUMPING OPERATION.

In many pump-turbines, within the ranges important for starting to turbine operation, for no-load and for extreme part-load conditions, the characteristic curves are S-shaped. This characteristic can be so strongly pronounced that operation may be unstable under certain conditions. The COO II pump turbines in Belgium showed such unstable behavior initially. This installation is, therefore, taken as an example for the discussion of the reasons and the measures that lead to an improvement in stability. An improvement in stability was achieved by providing for the opening of two individual wicket gates by means of special linkages and two additional small servo-motors, to an exactly determined pre-opening angle. As the asynchronous opening of wicket gates can appreciably affect the wicket gate torques, the more important results of the torque measurements conducted on the model are indicated and are compared with the results obtained in prototype tests.