Many industrial processes require variable speed load drive devices, such as pumps for varying liquid flow; fans for variation of air flow; transport systems to vary the transport speed; lathes for variation of cutting speed; winding machines to compensate for the variation of the coil diameter.

For a long time, variable speed industrial applications have been dictated by process requirements and limited by technology because of cost, efficiency and maintenance requirements and components employed. In the past, the speed variation was made by a fixed speed induction motor and was the first electric energy conversion device for mechanical energy, energy conversion device through mechanical, hydraulic or electromagnetic components (according to the energy conversion device.

A motor starting device joins all the components necessary to control and protect an electric motor and the selection of the components to constitute a device conditions the performance of the installation. The main components required are: protection level, fixed or variable speed operation, sectioning, protection against short circuits, protection against overload and switching.