Electric motor family tree

Electric Motor Family Tree

     After the introduction of the DC electrical distribution system by Edison in the United States, a gradual transition to the more economical AC system commenced. Lighting worked as well on AC as on DC. Transmission of electrical energy covered longer distances at lower loss with alternating current. However, motors were a problem with alternating current. Initially, AC motors were constructed like DC motors. Numerous problems were encountered due to chang-ing magnetic elds, as compared to the static elds in DC motor eld coils. Charles P. Steinmetz contributed to solving these problems with his investigation of hys-teresis losses in iron armatures. Nikola Tesla envisioned an entirely new type of motor when he visualized a spinning turbine, not spun by water or steam, but by a rotating magnetic eld. His new type of motor, the AC induction motor, is the workhorse of industry to this day. Its ruggedness and simplicity (Figure 13.1) make for long life, high reliability, and low mainte-nance. Yet small brushed AC motors, similar to the DC variety, persist in small appliances along with small Tesla induction motors. Above one horsepower (750 W), the Tesla motor reigns supreme. Modern solid state electronic circuits drive brushless DC motors with AC waveforms gen-erated from a DC source. The brushless DC motor, actually an AC motor, is replacing the conventional brushed DC motor in many applications. And, the stepper motor, a digital ver-sion of motor, is driven by alternating current square waves, again, generated by solid state circuitry. Figure 13.2 shows the family tree of the AC motors described in this chapter. Cruise ships and other large vessels replace reduction geared drive shafts with large multi-megawatt generators and motors. Such has been the case with diesel-electric locomotives on asmaller scale for many years.