Complex sentence: The turbine geometry (nozzle-runner-shaft) assures that the water jet is not made ineffective, hitting the shaft, as approximately ⅓ of the overall power is still transferred to the runner when the water is leaving the turbine.
Split into simpler sentences: The turbine geometry (nozzle-runner-shaft) assures that the water jet is effective, hitting the shaft. About ⅓ of the overall power is transferred to the runner when the water is leaving the turbine.