This study modernizes the runner of a Hapcheon hydropower plant installed with a vertical Francis turbine with a rated head
of 95 m, measures and compares the field efficiency before and after the modernization, and verifies how much influence the
runner has on the efficiency of the turbine. The same field test was performed using the thermodynamic method, which is a
test applicable to turbines exceeding 100 m head according to IEC 60041. Efficiency of the old runner was measured at 93.21%
as the highest efficiency point under the condition of head 113.0 m. Efficiency of the new runner was measured at a highest
efficiency of 94.20% despite the worse condition of head 115.75 m. The efficiency improved by about 1%p under the operating
conditions above about 50% turbine power output. It is meaningful in that the performance of HPP is improved by replacing
the runner.