The rise of renewable energies like solar and wind has transformed hydroelectric storage power plant operations, leading to more frequent starts and stops and accelerated wear on machine components. Previous studies have shown the potential to detect runner natural frequencies using sensors placed on the bearing of horizontal Pelton turbines. The present study explores the non-intrusive measurement of these frequencies during transient operations. Two vibration fingerprints and a transmissibility experiment were conducted during a runner replacement on a ternary unit at the Forces Motrices Hongrin Léman (FMHL) pumped storage power plant (PSP) in Switzerland. The ternary unit features two Pelton turbines mounted side by side on the same shaft. During the refurbishment of the unit, both runners were replaced at the same time. The vibration measurements aimed at understanding how the runners affected the power unit's dynamic behaviour and assess the feasibility of capturing the runners' natural frequencies from remote measurement positions. The transmissibility experiment conducted before replacing the runners reveals differences in the axial natural frequencies of the two original runners, ranging from 6 to 9 Hz (1.3% to 1.7%). Additionally, the experiment indicates an average attenuation of two orders of magnitude of the vibration level from the runners to the bearings. During startup transients measured with the original runners, frequencies which coincide with tangential and tangential in counter-phase mode of the runners are excited. In contrast, when analysing startup transients with the new runners, the results indicated that maximum amplitudes were concentrated within a higher frequency range, corresponding to the tangential and axial in counter phase natural frequencies of the new runner. The results are consistent with prior studies and suggest the potential for advanced non-intrusive vibration monitoring tools to improve Pelton turbine reliability and safety.