A JET INTERFERENCE OF A HIGH SPECIFIC SPEED PELTON TURBINE

摘要

On the rehabilitation and renewal hydraulic power plant, the downsizing by the higher rotating speed and the reducing unit number by increasing maximum output are the priority to cost saving. On the other hand, the higher speed of multi-jet Pelton turbine makes the jet interference that is the following phenomenon. The water jet into the bucket cannot be flowed out completely due to next jet inflow by the reason of high speed relatively. In such case, the jet interference occurs in the bucket and it leads extraordinary efficiency drop. This is one of the obstacles to the development of the higher specific speed Pelton turbine with multi-jet. The model test of the Pelton turbine is examined according to the standard before prototype design similar to other turbines. However, it is well known that the performance between model and prototype turbine does not correspond to the jet interference region. This problem is called the "Scale effect" generally. Therefore, it is difficult to predict the occurrence of jet interference for prototype turbine. The operating range of the prototype turbine was determined empirically so far. Consequently, the measurement of jet interference for the prototype turbine is important to define the scale effect. However, although there are few reports for the jet interference, the performance of the prototype turbine in this region is not measured on the field test. The authors measured the jet interference occurring region by the prototype turbine with high specific speed 6 nozzles Pelton turbine. To measure the jet interference, the net head and discharge of the field test is changing by adjusting the inlet valve and needle opening. The turbine discharge is measured by the 4-pass ultrasonic flow meter. This paper is reported that the occurrence point of the jet interference becomes clear by this field test.