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Flow friction theorem of Pelton turbine hydraulics

Abstract The flow friction in the rotating buckets of a Pelton turbine influences the system efficiency in both the direct and indirect ways. The direct influence is determined by the friction, which directly drives or retards the bucket motion and thus determines the power output. The indirect way is determined by the changes of relative flow and the pressure distribution in the bucket. The flow friction theorem derived in the current paper points out that the total reduction of the system efficiency is equal to the total efficiency reductions by two different ways. In the total efficiency reduction, the effect from the indirect way dominates. In addition, frictions in the bucket, whether at the bucket entrance or at the exit, always cause a reduction in the system efficiency. The efficiency drop resulting from the flow frictions represents the greatest part in the total loss in the system efficiency of a Pelton turbine and should in no case be neglected.