Variable speed booster sets assembled with two to three pumps each are equipped with a permanent magnet motor (IE5 efficiency level) and controlled by an e-SM frequency converter. The electric pumps used are the vertical multistage pumps of the e-SV Smart series, the vertical multistage step-coupled pumps of the VM Smart series or the horizontal multistage pumps of the e-HM Smart series. Each pump is equipped with an e-SM frequency converter that ensures variable speed operation on all electric pumps.