Revolving and Evolving-Early dc Machines

In an age largely characterized by information and communication technology (ICT), which uses more and more feeble currents, electrical power is also experiencing a period of excellent health and heads towards a bright future. This success is largely due to electric motors, which are available in different types and powered by direct current (DC) as well as alternating current (AC) sources, provided by power grids or by inverters at variable frequencies. Their versatility and ubiquity is so wide that they can be found almost everywhere: in many household appliances, technician power tools, building fans, factory machine tools, blowers and pumps of industrial fluid systems, cableways, railway and streetcar locomotives, computer disk drives, drivers and printers and cellphone vibration alerts. Tens of billions of electric motors are produced every year, with powers ranging from a few hundredths of a milliwatt to some tens of megawatts. Their future looks bright due to the rise of electric-powered transport, which will be enforced by government measures in many countries in the coming years.