Abstract：Adjusting speed with VFDs(Variable Frequency Drives)as an operational control method has been applied in bulb tubular pumping stations in the South-to-North Water Diversion Eastern Route Project in China. In order to study the performances and control mode of bulb tubular pumps with VFDs and guide the optimal operation, popularization and application of pump stations, the variable speed performances are analyzed in theory and tested in model systems for No3 Huaiying and Sihong pumping stations in this paper. According to modes of main electrical wirings with and without the bypass, the operational control methods are studied in various working heads considering the efficiencies of VFDs and the motor in various speeds. The conclusion is that the performances of bulb tubular pumps with VFDs are restricted by the performances of impellers and flow channels. Within a certain speed range, the similarity law with constant efficiency can be used to predict the perfor-mances of bulb tubular pumps. Another conclusion is that the loss of VFDs must be considered when determining the operation performances of the bulb tubular pump unit. At the same time, the changes in the efficiency of VFDs and motor caused by the change of frequency should be analyzed. And after considering the loss of VFDs and motor caused by the change of frequency, there are higher efficiencies without VFDs when the working head is about 40%-80% design head of water supply in Sihong Pumping Station.
