Wide-load operation in the turbine mode is increasingly required for pump turbines in pumped storage plants

yet the pressure pulsations in the turbine intensify notably under small-opening

low-load conditions

posing a potential threat to unit safety and stability. Using the pulsation tracing network (PTN) method

this study examines a pump-turbine with a five-long and five-short blade runner

focusing on analysis of the pressure pulsation characteristics in its vaneless section under different heads

different guide vane openings

and different loads in the turbine mode. The results reveal complicated pressure pulsation components in the vaneless section

including typical frequencies such as 0.33fn

1fn

3fn

5fn

and 10fn (fn for one tenth of the blade passing frequency)

and the ones of 10fn and 5 fn exert the most significant influence. The phase characteristic analysis further indicates the dominant frequency pulsations propagate upstream and downstream

affecting flow stability throughout the full passage. These findings provide valuable insights for optimizing pump-turbine runner design to enhance wide-load operational performance.