大中功率风机和泵采用变频调速可节约大量电能，大部分功率在0.2～2 MW范围中。我国现在200 kW以上的电机多是中压，现行中压电网多为10 kV，选用10 kV直接变频从技术和经济角度看都不太合理。由于变频器输入侧都有变压器，因此电机和变频器没有必要和电网一致。文章讨论不同功率段的合理电压等级以及在电机电压和电网电压不同情况下当变频器出现故障时如何实现旁路工作。

A large amount of energy will be saved if adjustable-speed drives are adopted by high and medium power pumps and fans. The power range of most of the drives is within 0.2～2 MW. The rated voltage of most of the motors in the power range is 10 kV because the power supply is 10 kV. The adjustable-speed scheme, a 10 kV motor is fed by a 10 kV inverter, is not reasonable because this kind of inverter consists of a lot of power electronic devices in series and its cost is high and reliability is poorer than lower voltage one. Owing to the existence of input transformer of the inverter, it is not necessary to ask for that the rated voltage of the motor and inverter is the same as power supply, i. e. a lower rated voltage can be used for the motor and inverter. The reasonable rated voltages of motors and inverters with different power grades are investigated and the by-pass methods when the rated voltages of the motors are different from power supply are discussed in this paper.